SEARCH

SEARCH BY CITATION

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

Background : While wintertime vitamin D deficiency has been well-documented in Crohn's disease patients, less is known about vitamin D status during summertime and whether a seasonal variation exists in bone turnover.

Aims : To compare vitamin D status and bone turnover markers in Crohn's disease patients with age- and sex-matched controls during late-summer and late-winter.

Subjects : Crohn's disease patients (n = 44; mean age 36.9 years, currently in remission) and matched controls (n = 44) were recruited from Cork University Hospital and Cork City area, respectively.

Methods : Bloods were analysed for 25-hydroxyvitamin D, parathyroid hormone, bone-specific alkaline phosphatase, osteocalcin and urine analysed for N-telopeptides of type 1 collagen.

Results : Serum 25-hydroxyvitamin D concentrations were significantly (P < 0.003) lower in Crohn's disease patients than in control subjects during both seasons. In Crohn's disease patients, serum 25-hydroxyvitamin D concentrations were lower (P < 0.0001) whereas serum parathyroid hormone, osteocalcin and bone-specific alkaline phosphatase and urinary N-telopeptides of type 1 collagen levels were higher (P < 0.001) during late-winter than late-summer.

Conclusion : There were notable seasonal variations in vitamin D status and bone turnover markers in Crohn's disease patients. The impact of winter decline in vitamin D status and increase in bone turnover on long-term risk of osteopenia/osteoporosis in Crohn's disease patients is unclear.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

Vitamin D is essential for intestinal calcium absorption and plays a central role in maintaining calcium homeostasis and skeletal integrity.1 Cutaneous biosynthesis upon exposure of the skin to ultraviolet B light is the major source of vitamin D for most people.2 Seasonal changes in serum 25-hydroxyvitamin D [25-(OH) D; the most commonly used index of vitamin D status3] have been well documented for healthy adult populations.4–7 Vitamin D status is highest in Northern European populations around late-summer (August–September) and lowest around late-winter (February–March).8 In northern latitudes of 40–60°N, sunlight is not of sufficient intensity during the winter months (October–March) to stimulate cutaneous synthesis of vitamin D.5 This creates an increased reliance on dietary sources during these winter months to help maintain adequate vitamin D status. However, the usual dietary vitamin D intake by many European populations is not sufficient to maintain adequate vitamin D status.3 For example, recent data from the Irish population show relatively low dietary intakes of vitamin D (<5 μg/day) in Irish adults, aged 18–64 years.9 Not surprisingly, hypovitaminosis D is common in Irish adults, especially during wintertime.10, 11

A wintertime insufficiency of vitamin D has been shown to have adverse effects on calcium metabolism, matrix ossification, the rate of bone turnover and bone mineral density (BMD).12, 13 Dawson-Hughes et al.14 measured spinal BMD in a group of postmenopausal women at 6-monthly intervals and showed a significant bone loss during December–January to June–July, and increase during June–July to December–January, with no net change over the 12-months. The decrease and subsequent increase in BMD in these women mirrored the seasonal fall and rise in serum 25-(OH) D levels and consequent increase and decrease in serum parathyroid hormone (PTH).14

While there is much current debate about the serum 25-(OH) D level which defines the cut-off for vitamin D deficiency/insufficiency (ranging from <20 to <100 nm),12, 13, 15, 16 suboptimal vitamin D status, irrespective of the definition applied, is common in patients with Crohn's disease (CD),1, 17–22 even in summertime.21–23 The suboptimal vitamin D status during summer in some patients may lead to a persistently elevated level of PTH and increased rates of bone turnover. For example, Haderslev et al.1 recently found that poor vitamin D status increased levels of biochemical markers of bone turnover and reduced BMD in a group of patients with small intestinal resection, predominantly CD patients. Furthermore, low vitamin D status may impede the natural rebound in bone mass that should occur during summer. Therefore, year-round suboptimal vitamin D status may contribute to the osteopenia and osteoporosis, common among CD patients. For example, osteopenia is seen in about 30% of CD patients, while 10–12% of patients have osteoporosis.24–26

Therefore, the objective of the present study was to evaluate vitamin D status of a group of Irish CD patients during late-summer and late-winter and compare it with that of a group of sex- and age-matched healthy control subjects, and furthermore, to investigate whether a seasonal variation exists in the rate of bone turnover in these patients, using biochemical markers of bone metabolism.27 The biochemical markers of bone metabolism chosen for the present study were urinary type 1 collagen cross-linked N-telopeptides (NTx; a specific and sensitive marker of bone resorption;28) and serum osteocalcin and bone-specific alkaline phosphatase (specific and sensitive markers of bone formation29).

Methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

Subjects

Patients attending the Cork University Hospital IBD Clinic were sent a research information bulletin which provided information about the present study. Consecutive patients, in whom there was a confirmed diagnosis of CD and who were in clinical remission, were included from those who volunteered for the study after receiving the research information bulletin. No patient refused entry to the study after being interviewed and informed of the requirements and details. CD was previously diagnosed on the basis of consistent clinical findings, barium radiology and histology. Remission was defined at the time of study as the absence of gastrointestinal symptoms and not requiring therapeutic doses of corticosteroids. A total of 44 CD patients (15 male, 29 female) were included in the study in September–October 2002. Healthy control subjects, without disorders of the gastrointestinal tract or bone, were recruited from the Cork City area by means of advertisement in local print media, local radio and wide distribution of information leaflets. A database of willing healthy control volunteers (n = 66) for the study was generated and a total of 44 control subjects were selected for inclusion in the study on the basis of matching for age- (within 2 years of age maximum) and gender to the 44 CD patients. Mean age, weight, height, body mass index (BMI), disease duration and the ratio of males to females for the patient population and age- and sex-matched healthy controls at baseline are provided in Table 1. Of the 44 CD patients who presented at the first visit, 40 patients (15 male, 25 female) returned for a second visit in March 2003. Of these 40 patients, eight patients were in the active phase of disease.

Table 1.  Baseline characteristics of patients with CD (n = 44) compared with age- and sex-matched healthy control subjects (n = 44)
 CD patientsControl subjectsP-value*
Means.d.Means.d.
  1. * Comparison of mean values between CD patients and age- and sex-matched control subjects, where appropriate, using unpaired Student's t-test.

  2. BMI, body mass index; CD, Crohn's disease.

Age (years)36.911.136.711.00.939
Height (m)1.680.111.680.090.860
Weight (kg)70.817.568.410.80.449
BMI (kg/m2)24.95.424.33.30.543
Disease duration10.58.5 
Males/females15/2915/29

At baseline, the mean length of remission was 27 months (range: 2–84). The mean erythrocyte sedimentation rate was 9 (2–21/h) and only two patients had modestly elevated C-reactive protein concentration of 28 (normal: <10 mg/L). The mean serum albumin concentration was 37 g/L with only two patients having a low level (25 and 28 g/L). All patients were on maintenance 5-aminosalicylates (2–3 g/day), eight were taking mercaptopurine (6-mercaptopurine; 50 mg/day) or azathioprine (100 mg/day). No patients were taking warfarin or methotrexate. None had received infliximab or other antitumour necrosis factor (TNF) therapy. Only one patient was taking a low dose of steroid (prednisolone, 5 mg/day) throughout the study period. Twenty-nine patients had not received systemic steroids within the previous 2 years; 15 had received at least one course of oral steroids (commencing with oral prednisolone 40 mg/day and tapering over 12 weeks) during the previous 2 years (mean: two courses; range: 1–5). Four patients had received antibiotics (metronidazole in each case) within the past year and only one was taking metronidazole (200 mg b.d.) at the time of the first sampling point. Seven of the patients had small bowel involvement only, five patients had inflammation of the colon and 32 had inflammation in both sites. Twenty-six patients had a previous terminal ileal resection (<50 cm) and none ever had steatorrhea or short bowel syndrome. Of those who had surgery, only one patient had more than one resection (two resections).

Five female patients and five female control subjects were postmenopausal; of those three patients and two control subjects were receiving hormone replacement therapy (HRT). Six female CD patients and six control females were taking oral contraceptive medications. None of the patients or controls was taking activated forms of vitamin D [25-(OH) D or 1,25-(OH)2D], PTH, calcitonin, anticonvulsants or bisphosphonates, while six patients and four controls were regular cigarette smokers.

At the first visit, 15 patients (approximately 32%) and 13 controls (approximately 30%) were taking vitamin D-containing supplements (in the range 2.5–20 μg/day), while at the second visit, 14 patients (approximately 44%) and 12 controls (approximately 38%) were taking vitamin D-containing supplements.

Ethical considerations

Before participation in this study, all subjects signed an informed consent document approved by the Clinical Research Ethics Committee of the Cork Teaching Hospitals.

Design

Each participant was invited to provide a fasting blood and urine sample at the University during September–October (late-summer) 2002 and again during March (late-winter) 2003. After an overnight fast, a blood sample (20 mL) was taken between 08:30 and 10:30 hours by a trained phlebotomist. Calcium and vitamin D intake was assessed, once, at the first visit, by use of a 128-item validated food frequency questionnaire (FFQ)30 by a trained investigator. In particular, the FFQ included foods that contributed 95% of vitamin D intakes in the Irish population and the frequencies of consumption of such foods were reported on an increasing, 9-level scale, ranging from never or <1 serving/month to ≥4 servings/day. The food portion sizes were estimated using a photographic food atlas where possible,31 and for other food items a standard portion size was assumed.32 Updated vitamin D food compositional data for Irish foods9 were used in estimating vitamin D intake values.

Collection and preparation of samples

Blood was collected by venepuncture into a vacutainer tube with no additive and processed to serum, which was immediately stored at −80 °C until required for analysis. Subjects were supplied with suitable collection containers for urine samples and asked to collect first morning void urine samples. Portions of urine were stored at −20 °C from the morning of collection until required for analysis.

Experimental techniques

Urinary creatinine.  Creatinine was determined in urine samples using a diagnostic kit (Metra Creatinine Assay Kit, catalogue no. 8009, Quidel Corporation, San Diego, CA, USA). The intra- and inter-assay coefficient of variation (CV) was 1.6% and 4.3%, respectively.

Urinary type 1 collagen cross-linked N-telopeptides.  Type 1 collagen cross-linked N-telopeptides was measured in the urine samples by an enzyme-linked immunosorbent assay (ELISA; Osteomark, Ostex International, Inc., WA, USA). The intra- and inter-assay CV was 6% and 5%, respectively.

Serum intact parathyroid hormone.  Serum intact parathyroid hormone (iPTH) levels were measured in serum using an ELISA (OCTEIA iPTH, Immuno Diagnostic Systems Ltd, Boldon, UK). The intra- and inter-assay CV was 3.4% and 3.8%, respectively. Based on the manufacturer's information the suggested normal range for PTH is 0.8–3.9 pm, while values between 4.1 and 29.0 pm are suggestive of primary hyperparathyroidism.

Serum 25-hydroxyvitamin D.  Serum 25-(OH) D levels were measured in serum samples using a recently developed ELISA (OCTEIA 25-(OH) D, Immuno Diagnostic Systems Ltd). The intra- and inter-assay CV were 5.9% and 6.6%, respectively. The quality and accuracy of our serum 25-(OH) D analysis is assured on an ongoing basis by participation in the Vitamin D External Quality Assessment Scheme (DEQAS; Charing Cross Hospital, London, UK). There is no international consensus on cut-off levels for vitamin D deficiency and vitamin D insufficiency.8, 16 Therefore, for illustrative and comparative purposes in the present study, two suggested sets of serum 25-(OH) D cut-off values for defining vitamin D status were used. These include the definitions of vitamin D status suggested by Heaney and Weaver33 (<80 nm, insufficient; >80 nm sufficient) and Lips13 (>50 nm, replete; 25–50 nm, mildly deficient; 12.5–25 nm, moderately deficient; <12.5 nm, severely deficient).

Serum osteocalcin.  Osteocalcin levels were measured in serum samples using an ELISA (Metra Osteocalcin EIA Kit, Quidel Corporation). The intra- and inter-assay CV was 6.0% and 7.6%, respectively.

Serum bone-specific alkaline phosphatase.  Bone-specific alkaline phosphatase activity was measured in serum samples using an ELISA (Metra Osteocalcin EIA Kit, Quidel Corporation). The intra- and inter-assay CV was 5.0% and 5.9%, respectively.

Statistical analysis

Prior to the start of the study, the required sample size at α = 0.05 and β = 0.80 was calculated34 using the variability around the mean serum 25-(OH) D levels in Irish adults and a selected minimum detectable percentage difference in serum 25-(OH) D within groups (i.e. because of seasonal variation within CD patients and healthy controls, separately) of 30% and between subject groups (i.e. CD patients vs. healthy controls) of 25%. The value of 30% for seasonal effects was chosen as this is the magnitude of reported change in serum 25-(OH) D levels from winter to summer in healthy Irish adults,35 whereas the value of 25% was chosen as this is the reported magnitude of difference in serum 25-(OH) D levels between adults CD patients and healthy adult controls.17 On the basis of these calculations we estimated that we needed 30 subjects per group; however, owing to the possibility that the disease would become active by the second visit in up to 20% of the CD patients, and accounting for possible drop-outs, we recruited 44 subjects per group. Data are presented as mean values and standard deviations. Data for all variables (except for dietary intakes) were normally distributed and allowed for parametric tests of significance. Differences in age, height, weight and BMI between the patients and matched healthy control subjects were examined by unpaired Student's t-test. Differences in dietary calcium and vitamin D intakes between the patients and matched healthy control subjects were examined by Mann–Whitney tests. Differences in dietary calcium and vitamin D intakes from all sources (food and supplements) and from food sources only, within a subject group were examined by Wilcoxon matched pairs signed ranks tests. Data from CD patients who were in the active phase of the disease during the second sampling period were omitted from the within- and between-group (visit 2) statistical analyses. Comparisons of biochemical variables between patients and controls within a season were made by unpaired Student's t-tests. Between-season comparisons of biochemical variables in patients and controls, separately, were made by paired Student's t-tests. Differences in proportion of patients and control subjects that were vitamin D-deficient/insufficient, within a season, were assessed by chi-square tests. The Statistical Package for the Social Sciences (SPSS for Windows Version 10.0, SPSS Inc., Chicago, IL, USA) was used for statistical analysis.

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

Baseline characteristics of subjects

There were no significant differences between the patients with CD and age- and sex-matched healthy control subjects for age, weight, height, or BMI (Table 1).

Dietary intakes of vitamin D and calcium

The mean daily intakes of vitamin D and calcium from all sources (i.e. food and supplements) and food alone, assessed during the first visit (September–October 2002), were similar in CD patients (currently in clinical remission) and healthy controls (Table 2). Within both groups, the mean daily intakes of vitamin D and calcium from food sources alone were significantly increased when vitamin D- (P < 0.001) and calcium-containing (P < 0.01) supplement use was accounted for (Table 2).

Table 2.  Mean daily intakes of vitamin D and calcium from all sources (i.e. food and supplements) and from food sources only in Crohn's disease (CD) patients (n = 44) and age- and sex-matched healthy control subjects (n = 44)
 CD patientsControl subjectsP-value*
Means.d.Means.d.
  1. * Comparison of mean values between CD patients and age- and sex-matched control subjects using Mann–Whitney test.

  2. Mean intake value from food sources only was significantly different from mean intake value from all sources, using Wilcoxon matched pairs signed ranks test; **P < 0.01, ***P < 0.001.

All sources
 Calcium (mg)149175012845240.342
 Vitamin D (μg)6.75.16.74.80.986
Food sources
 Calcium (mg)1396**7311240**5120.653
 Vitamin D (μg)4.4***1.94.7***2.90.826

Seasonal variation in serum 25-(OH) D and impact on serum PTH

Mean serum 25-(OH) D concentrations were significantly (P < 0.003) lower in CD patients (currently in clinical remission) than in healthy control subjects during both sampling points (i.e. late-summer and late-winter; Table 3). Within-group comparisons show that serum 25-(OH) D concentrations were significantly (P < 0.018) lower during late-winter compared with late-summer both in CD patients and healthy controls (Table 3). Of note, the mean serum 25-(OH) D concentration of the CD patients during late-summer (75.0 nm; a time when vitamin D status is expected to be at its highest) was similar to levels in healthy controls during late-winter (80.1 nm; a time when vitamin D status is expected to be at its lowest).

Table 3.  Serum 25-(OH) D and parathyroid hormone and markers of bone turnover in Crohn's disease (CD) patients and age- and sex-matched control subjects during late-summer and late-winter
 Late-summer 2002Late-winter 2003
CD patients (n = 44)Control subjects (n = 44)CD patients (n = 32)Control subjects (n = 32)
Means.d.Means.d.Means.d.Means.d.
  1. 25-(OH) D, 25-hydroxyvitamin D; PTH, parathyroid hormone; NTx, type I collagen cross-linked N-telopeptides; BCE, bone collagen equivalents.

  2. Mean values significantly different from that of control subjects, within a season, using unpaired Student's t-test; *P < 0.05, **P < 0.01.

  3. Mean values significantly different from that during late-winter, within patients and controls, separately, using paired Student's t-test; †P < 0.05, ††P < 0.001, †††P < 0.0001.

Serum
 25-(OH) D (nm)75.0**†††28.7105.3†55.556.6**22.180.143.6
 PTH (pm)2.06†††1.211.85†††0.893.161.792.651.48
 Osteocalcin (μg/mL)10.9†††4.711.1†††3.516.25.514.64.0
 Bone-specific alkaline phosphatase (U/L)22.7†††8.420.47.026.8**8.420.66.3
Urine
 NTx (nmol BCE/mmol creatinine)60.4*††31.844.7†††24.383.2**41.658.132.9

In a subanalysis of the data, subjects within both groups were stratified into ‘users’ and ‘non-users’ of vitamin D-containing supplements, which revealed that a significant seasonal variation in serum 25-(OH) D concentrations existed in subjects (CD patients or healthy controls) not taking vitamin D-containing supplements, with late-winter values significantly (P < 0.003) lower than late-summer values (see Figure 1). On the contrary, there was no seasonal variation (P > 0.65) in serum 25-(OH) D concentrations in subjects (CD patients or healthy controls) taking vitamin D-containing supplements (see Figure 1).

image

Figure 1. Serum 25-hydroxyvitamin D [25-(OH) D] in Crohn's disease (CD) patients and healthy control subjects, stratified by season and supplemental vitamin D use. Open bars (supplement users) and grey bars (supplement non-users). *Mean values significantly lower than that of late-summer 2002; using paired Student's t-tests; P < 0.003.

Download figure to PowerPoint

There were no significant differences in mean serum PTH concentrations between CD patients and healthy control subjects at either sampling point (Table 3). Within-group comparisons show that serum PTH concentrations were significantly (P < 0.0002) higher during late-winter compared with summertime both in CD patients and healthy controls (Table 3).

Prevalence of vitamin D deficiency/insufficiency in CD patients and healthy controls

During late-summer, two of 44 and eight of 44 healthy controls and CD patients, respectively, were vitamin D-deficient (defined as serum 25-(OH) D levels <50 nm),13) a difference which was significant (P < 0.05). In all of the deficient subjects, the vitamin D deficiency was in the mild deficiency range (25–50 nm).13 During late-winter, eight of 32 and 16 of 32 healthy controls and CD patients, respectively, were vitamin D-deficient (defined as serum 25-(OH) D levels <50 nm),13 a difference which was significant (P < 0.05). In the case of controls, all eight had vitamin D deficiency in the mild deficiency range (25–50 nm), whereas three and 13 of the CD patients could be classified as moderately and mildly deficient (defined as serum 25-(OH) D levels 12.5–25 nm and <50 nm),13 respectively. If the higher cut-off value of serum 25-(OH) D (namely <80 and ≥80 nm for vitamin D insufficiency and sufficiency, respectively33) was applied then during late-summer, 14 of 44 and 27 of 44 healthy controls and CD patients, respectively, were vitamin D insufficient, a difference which was significant (P < 0.01). During late-winter, 18 of 32 and 27 of 32 of healthy controls and CD patients, respectively, were vitamin D insufficient, a difference which was significant (P < 0.01).

Markers of bone turnover in CD patients and healthy controls

Mean serum osteocalcin concentrations were similar in CD patients and healthy control subjects during late-summer and late-winter (Table 3). While mean serum bone-specific alkaline phosphatase concentrations were significantly (P < 0.01) higher in CD patients than in healthy control subjects during late-winter, concentrations were similar (P = 0.167) in both groups during late-summer (Table 3).

Within-group comparisons show that serum osteocalcin concentrations were significantly (P < 0.0001) higher during late-winter compared with late-summer both in healthy controls and CD patients (Table 3). While serum bone-specific alkaline phosphatase concentrations were similar (P = 0.136) during late-summer and late-winter in healthy controls, they were significantly higher (P < 0.01) in CD patients during late-winter compared with late-summer (Table 3).

Mean urinary NTx concentrations were significantly higher (P < 0.05) in CD patients than healthy control subjects during both time-points (Table 3). Within-group comparisons show that urinary NTx concentrations were significantly (P < 0.001) higher during late-winter than late-summer both in healthy controls and CD patients (Table 3).

Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

In the present study, mean urinary NTx levels in CD patients were significantly higher than those in age- and sex-matched control subjects, whereas serum levels of osteocalcin were similar in both groups. While serum levels of bone-specific alkaline phosphatase were also similar in both groups during summer 2002, levels were significantly higher in CD patients during winter 2003. The reasons for the discordant findings between the two markers of bone formation during wintertime are unclear. It is possible that serum bone-specific alkaline phosphatase is a more sensitive marker of bone formation than serum osteocalcin and, therefore, may be more likely to be elevated in CD patients compared with healthy controls during winter as a consequence of significantly lower vitamin D status in patients.

The present findings of increased levels of urinary NTx and, in general, no difference in bone formation marker levels (with the exception of bone-specific alkaline phosphatase during wintertime) between CD patients and healthy controls are in broad agreement with similar findings of some, but not all,36, 37 studies of IBD patients which reported increased levels of bone resorptive markers without a compensatory increase in formation markers.24, 38–40 Dresner-Pollak et al.27 recently showed, using quartile analysis that IBD patients with the highest urinary NTx levels experienced the greatest decrease in spinal BMD over a 2-year period compared to patients with the lowest NTx levels.

The elevated rates of bone resorption observed in CD patients in the present study may explain, at least in part, the osteopenia and osteoporosis which are common among patients with CD.24, 25 While there may be several factors underpinning the elevated rates of bone resorption in these patients, two of the principal reasons that have been put forth as causative factors for the osteopenia in CD, namely, high dosage steroid use18, 41 and an active inflammation process,42 were not factors in the patients in the present study. While two patients had modestly elevated C-reactive protein concentrations, which might be suggestive of subclinical activity, all patients met our entry criterion of clinical remission. Inadequate vitamin D has been suggested as an aetiological factor for CD-associated osteopenia.1, 43, 44

In the present longitudinal study, CD patients exhibited a seasonal variation in serum 25-(OH) D and PTH levels as well as in levels of serum- and urinary-based biochemical markers of bone turnover. This seasonal variation in biochemical indices was also observed in the healthy control subjects. However, despite displaying a seasonal variation, the vitamin D status of CD patients was significantly lower than that of age- and sex-matched healthy control subjects, during winter- but also summer-time. Indeed, the mean serum 25-(OH) D concentration of the CD patients during late-summer (a time when vitamin D status is expected to be at its highest10) was similar to levels in healthy controls during late-winter (a time when vitamin D status is expected to be at its lowest10). Furthermore, during both seasons, at least twice as many CD patients had inadequate vitamin D status (defined as serum 25-(OH) D <50 nm13) compared with healthy matched control subjects. These findings are in line with those of several, but not all,21, 45 studies which show vitamin D status to be lower in CD patients than control subjects or a healthy population reference range.1, 17, 21, 22, 44, 46

In Northern latitudes of 40–60°N, including Ireland at 51–55°N, sunlight is not of sufficient intensity during the winter months (October–March) to stimulate cutaneous synthesis of vitamin D.5 This creates an increased reliance on dietary sources during these winter months to help maintain adequate vitamin D status. The mean daily intake of vitamin D (from food sources alone as well as from food and supplements) was similar in CD patients and control subjects, suggesting that the difference in vitamin D status between the two groups, especially during wintertime, does not appear to relate to vitamin D intake. Although not determined in the present study, it is possible that a reduced efficiency of intestinal absorption of vitamin D, as a consequence of ileopathy,1, 47 a disrupted enterohepatic circulation of vitamin D,43 and/or renal insufficiency48 may have contributed to the lower status in CD patients compared with the control subjects. Other potential determinants of vitamin D status, such as BMI, gender, smoking and calcium intake,3, 49, 50 were similar in both groups. In addition, a lower exposure of CD patients to adequate sunshine during summer could not be discounted as a contributory factor.

Even though the CD patients had lower vitamin D status than sex- and age-matched controls, their mean serum 25-(OH) D levels were, on average, relatively good. For example, much lower mean serum 25-(OH) D levels and/or higher prevalence of low vitamin D status among adult CD patients have been reported compared with that observed in the present study.1, 17, 19, 21, 22, 46 For example, in a comparable study with the present one, Schoon et al.19 reported that the mean serum 25-(OH) D of a group of male and female patients with long-standing CD (mean age: 42 years) in the Netherlands, and who were in remission, was 28.4 nm during April/May and 35% had very low levels of 25-(OH) D (<25 nm). It must be emphasized, however, that vitamin D status is strongly influenced by geographical differences,15 making between-country comparisons difficult to interrupt. In comparison with other healthy Irish population subgroups, which had wintertime serum 25-(OH) D levels assessed the same year, the CD patients had at least similar, if not higher, mean serum 25-(OH) D levels compared with those of 50–70-year-old women [mean (s.d.): 68.6 (34.9), n = 479), 70–75-year-old women [mean (s.d.): 41.9 (21.1), n =4151) and 11–13-year-old girls [mean (s.d.): 29.7 (10.7), n = 2051). This is the first study, to our knowledge, which has investigated the vitamin D status of CD patients in Ireland, despite our relatively northerly latitude (51–55°N).

The relatively good vitamin D status of these Irish CD patients was, at least in part, because of their dietary intake of the vitamin as well as their use of supplemental vitamin D. The mean daily intake (from food sources only) of the CD patients was 4.4 μg/day, however, a high proportion (32–44%) of the patients used vitamin D-containing supplements, even in summertime, and when this was accounted for, the mean daily intake increased to 6.7 μg/day. Bernstein et al.52 estimated that vitamin D intake in adult female Canadian IBD (predominantly CD) patients was 3.6 μg/day from diet and when intake from vitamin D supplements were included, the mean total vitamin D intake was 7.1 μg/day. Two American studies have reported mean daily intakes of vitamin D of 3.2 μg and 5.3 μg, respectively, in IBD/CD patients.53, 54 The mean daily intake of a nationally representative sample of healthy Irish adults, aged 18–64 years, was 4.2 μg from food and supplements and 3.2 μg from food sources only.9 Use of vitamin D-containing supplements in this representative sample of healthy Irish adults was only 15%.55 Daily vitamin D supplement (20 μg) use is recommended for IBD patients that are receiving systemic steroids.18 The CD patients in the present study were in remission and not taking steroids, however, they may have continued the practise of taking supplemental vitamin D as a prophylactic measure even after ceasing steroid treatment, which might explain the high proportion of supplement users. Haderslev et al.1 reported that of a group of adult patients with small intestinal resection (predominantly CD patients) about 57% were taking oral vitamin D supplementation, even though these patients were in remission. The CD patients in the present study also had a relatively high mean calcium intake, which has been linked to a sparing effect of serum 25-(OH) D levels.3

An interesting finding was the lack of seasonal variation in serum 25-(OH) D levels in CD patients taking vitamin D-containing supplements, suggesting that supplement use (even with supplements containing 7.5 μg, on average) were to some degree protective of vitamin D status during wintertime. This lack of seasonal variation in serum 25-(OH) D levels in subjects taking vitamin D-containing supplements has also recently been reported for Irish postmenopausal women.10 However, the level of protection offered by vitamin D-containing supplements depends on the serum 25-(OH) D cut-off values of vitamin D adequacy/sufficiency applied; a hotly debated topic at present.12, 13 In the present study, 100% and approximately 85% of the CD patients taking vitamin D-containing supplements had adequate vitamin D status [defined as serum 25-(OH) D >40 nm56 and >50 nm,13 respectively] during wintertime. However, if a serum 25-(OH) D cut-off level of >80 nm33 is applied, then a much lower proportion (approximately 31%) of the CD patients taking vitamin D-containing supplements had sufficient vitamin D status during wintertime, suggesting that higher levels of vitamin D supplementation may be required. The recommended level of supplemental vitamin D for CD patients undergoing steroid treatment is 20 μg/day.18 Interestingly, and in line with this recommendation, Dawson-Hughes et al.14 reported that at an intake of least 20 μg/day are required to prevent osteoporosis. In the present study, only two of the 44 CD patients had an intake of 20 μg/day or more, and neither was able to achieve this dietary intake without using supplements. It may be timely to consider whether use of vitamin D supplements, especially during winter, should be a more general recommendation for CD patients rather than reserved for only those patients undergoing steroid treatment.

There have been several well-designed longitudinal studies which show a seasonal variation in serum 25-(OH) D as well as in sensitive and specific biochemical markers of bone turnover in healthy adults,57–61 although some studies failed to find an effect on biochemical markers even though there was a seasonal variation in serum 25-(OH) D.62–64 Seibel et al.65 on recently reviewing these studies remarked that all longitudinal studies reporting seasonal variation in bone turnover markers also observed a significant seasonal variation in serum PTH levels, whereas seasonal changes in serum PTH were always absent in the negative studies. The reasons for this are unclear. In the present longitudinal study, levels of serum 25-(OH) D and PTH, as well as biochemical markers of bone turnover exhibited seasonal variation, in CD patients. To our knowledge, there has been no other published longitudinal study, which investigated whether seasonal variation exists in bone turnover marker levels in CD patients. It is likely that in both CD patients and healthy controls in the present study, transiently elevated levels of PTH, secondary to suboptimal vitamin D status, may be the driving force behind the winter increase in markers of bone turnover. Of interest, Dawson-Hughes et al.14 showed that supplementation of postmenopausal women with 10 μg vitamin D attenuated the winter decrease in spinal BMD loss and fall and rise in serum 25-(OH) D and PTH, respectively, and over 12 months led to significant overall gain in spinal BMD (0.85%).

In conclusion, CD patients (currently in remission and receiving no or very low doses of steroids) had significantly higher levels of markers of bone resorption, but not of bone formation compared with age- and sex-matched control subjects. CD patients had significantly lower vitamin D status during winter- and summer-time compared with age- and sex-matched control subjects, despite similar intakes of vitamin D. There was a notable seasonal variation in biochemical indices of vitamin D status and bone turnover in the CD patients. It is unclear whether the winter decrease in vitamin D status and increase in the rate of bone turnover, increases the long-term risk of osteopenia and osteoporosis in CD patients. It would be of interest to study the impact of preventing or minimized the winter decrease in vitamin D status, by vitamin D supplementation throughout winter, on bone turnover and bone mass in CD patients.

Acknowledgement

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

This study was supported by funding made available under the National Development Plan 2000–2006 with assistance from the European Regional Development Fund.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References
  • 1
    Haderslev KV, Jeppesen PB, Sorensen HA, Mortensen PB, Staun M. Vitamin D status and measurements of markers of bone metabolism in patients with small intestinal resection. Gut 2003; 52: 6538.
  • 2
    Parfitt AM, Gallagher JC, Heaney RP, Johnston CC, Neer R, Whedon GD. Vitamin D and bone health in the elderly. Am J Clin Nutr 1982; 36: 101431.
  • 3
    Van Der Wielen RPJ, Lowik MRH, Van Den Berg H, et al. Serum vitamin D concentrations among elderly people in Europe. Lancet 1995; 346: 20710.
  • 4
    McKenna MJ, Freaney R, Meade A, Muldowney FP. Hypovitaminosis D and elevated serum alkaline phosphatase in elderly Irish people. Am J Clin Nutr 1985; 41: 1019.
  • 5
    Webb AR, Kline LW, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab 1988; 67: 3738.
  • 6
    Krall EA, Sahyoun N, Tannenbaum S, Dallal GE, Dawson-Hughes B. Effect of vitamin D intake on seasonal variations in parathyroid hormone secretion in postmenopausal women. N Engl J Med 1989; 321: 177783.
  • 7
    Rapuri PB, Kinyamu HK, Gallagher JC, Haynatzka V. Seasonal changes in calciotropic hormones, bone markers, and bone mineral density in elderly women. J Clin Endocrinol Metab 2002; 87: 202432.
  • 8
    McKenna MJ. Differences in vitamin D status between countries in young adults and the elderly. Am J Clin Nutr 1992; 93: 6977.
  • 9
    Hill TR, O'Brien MM, Kiely M, Flynn A, Cashman KD. Vitamin D intakes in 18–64 year-old Irish adults. Eur J Clin Nutr 2004; 58: 150917.
  • 10
    Hill TR, Collins A, O'Brien MM, Kiely M, Flynn A, Cashman KD. Vitamin D intake and status in Irish postmenopausal women. Eur J Clin Nutr 2004; 22 December (Epub ahead of print).
  • 11
    Doyle L, Jewell C, Mullen A, Nugent AP, Roche HM, Cashman KD. Effect of dietary supplementation with conjugated linoleic acid on markers of calcium and bone metabolism in healthy adult men. Eur J Clin Nutr 2005; 59: 43240.
  • 12
    Holick MF. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease and osteoporosis. Am J Clin Nutr 2004; 79: 36271.
  • 13
    Lips P. Which circulating level of 25-hydroxyvitamin D is appropriate? J Steroid Biochem Mol Biol 2004; 89–90: 6114.
  • 14
    Dawson-Hughes B, Dallal GE, Krall EA, Harris S, Sokoll LJ, Falconer G. Effect of vitamin D supplementation on wintertime and overall bone loss in healthy postmenopausal women. Ann Intern Med 1991; 115: 50512.
  • 15
    Ovesen L, Andersen R, Jakobsen J. Geographical differences in vitamin D status, with particular reference to European countries. Proc Nutr Soc 2003; 62: 81321.
  • 16
    Zittermann A. Vitamin D in preventive medicine: are we ignoring the evidence? Br J Nutr 2003; 89: 55272.
  • 17
    Driscoll RH Jr, Meredith SC, Sitrin M, Rosenberg IH. Vitamin D deficiency and bone disease in patients with Crohn's disease. Gastroenterology 1982; 83: 12528.
  • 18
    Scott EM, Gaywood I, Scott BB. Guidelines for osteoporosis in coeliac disease and inflammatory bowel disease. British Society of Gastroenterology. Gut 2000; 46: S1S8.
  • 19
    Schoon EJ, Müller MCA, Vermeer C, Schurgers LJ, Brummer R-JM, Stockbrugger RW. Low serum and bone vitamin K status in patients with longstanding Crohn's disease: another pathogenetic factor of osteoporosis in Crohn's disease? Gut 2001; 48: 4737.
  • 20
    Jahnsen J, Falch JA, Mowinckel P, Aadland E. Vitamin D status, parathyroid hormone and bone mineral density in patients with inflammatory bowel disease. Scand J Gastroenterol 2002; 37: 1929.
  • 21
    Harries AD, Brown R, Heatley RV, Williams LA, Woodhead S, Rhodes J. Vitamin D status in Crohn's disease: association with nutrition and disease activity. Gut 1985; 26: 1197203.
  • 22
    Andreassen H, Rix M, Brot C, Eskildsen P. Regulators of calcium homeostasis and bone mineral density in patients with Crohn's disease. Scand J Gastroenterol 1998; 33: 108793.
  • 23
    Siffledeen JS, Siminoski K, Steinhart H, Greenberg G, Fedorak RN. The frequency of vitamin D deficiency in adults with Crohn's disease. Can J Gastroenterol 2003; 17: 4738.
  • 24
    Bjarnason I, Macpherson A, Mackintosh C, Buxton-Thomas M, Forgacs I, Moniz C. Reduced bone density in patients with inflammatory bowel disease. Gut 1997; 40: 22833.
  • 25
    Szulc P, Meunier PJ. Is vitamin K deficiency a risk factor for osteoporosis in Crohn's disease? Lancet 2001; 357: 19956.
  • 26
    Vestergaard P. Bone loss associated with gastrointestinal disease: prevalence and pathogenesis. Eur J Gastroenterol Hepatol 2003; 15: 8516.
  • 27
    Dresner-Pollak R, Karmeli F, Eliakim R, Ackerman Z, Rachmilewitz D. Increased urinary N-telopeptide cross-linked type 1 collagen predicts bone loss in patients with inflammatory bowel disease. Am J Gastroenterol 2000; 95: 699704.
    Direct Link:
  • 28
    Rosen HN, Dresner-Pollak R, Moses AC, et al. Specificity of urinary excretion of cross-linked N-telopeptides of type I collagen as a marker of bone turnover. Calcif Tissue Int 1994; 54: 269.
  • 29
    Watts NB. Clinical utility of biochemical markers of bone remodeling. Clin Chem 1999; 45: 135968.
  • 30
    Collins A, O'Brien MM, Flynn A, Cashman KD, Kiely M. Comparison of a 69-item food frequency questionnaire (FFQ) with a 14-day dietary (DH) to estimate vitamin D intakes in 50–75-year-old Irish women. Proc Nutr Soc 2003; 62: 21A.
  • 31
    Ministry of Agriculture, Fisheries and Food. A Photographic Atlas of Food Portion Sizes. London, UK: Ministry of Agriculture, Fisheries and Food, 1997.
  • 32
    Food Standards Agency. Food Portion Sizes, 3rd edn. London, UK: TSO, 2002.
  • 33
    Heaney RP, Weaver CM. Calcium and vitamin D. Endocrinol Metab Clin North Am 2003; 32: 18194.
  • 34
    Dallal GE. PC-size consultant – a program for sample size determinants. Am Stat 1990; 44: 243.
  • 35
    Hill TR. Vitamin D intake and status of Irish subjects and the impact of vitamin D intake and status on bone turnover in Irish postmenopausal women. PhD thesis. Cork, Ireland: National University of Ireland, 2004.
  • 36
    Martin A, Fries W, Luisetto G, et al. Bone density and calcium metabolism in patients with long-standing quiescent Crohn's disease. Eur J Gastroenterol Hepatol 1994; 6: 6116.
  • 37
    Schoon EJ, Geerling BG, Van Dooren IM, et al. Abnormal bone turnover in long-standing Crohn's disease in remission. Aliment Pharmacol Ther 2001; 15: 78392.
  • 38
    Silvennoinen JA, Risteli L, Karttunen TJ, Risteli J. Increased degradation of type I collagen in patients with inflammatory bowel disease. Gut 1996; 38: 2238.
  • 39
    Bischoff SC, Herrmann A, Goke M, Manns MP, von Zur Muhlen A, Brabant G. Altered bone metabolism in inflammatory bowel disease. Am J Gastroenterol 1997; 92: 115763.
  • 40
    Robinson RJ, Iqbal SJ, Abrams K, Al-Azzawi F, Mayberry JF. Increased bone resorption in patients with Crohn's disease. Aliment Pharmacol Ther 1998; 12: 699705.
  • 41
    Silvennoinen JA, Karttunen TJ, Niemelä SE, et al. A controlled study of bone mineral density in patients with inflammatory bowel disease. Gut 1995; 37: 716.
  • 42
    Dresner-Pollak R, Karmeli F, Eliakim R, Ackerman Z, Tabb K, Rachmilewitz D. Femoral neck osteopenia in patients with inflammatory bowel disease. Am J Gastroenterol 1998; 93: 148390.
    Direct Link:
  • 43
    Arnaud SB, Goldsmith RS, Lambert PW, Go VL. 25-Hydroxyvitamin D3: evidence of an enterohepatic circulation in man. Proc Soc Exp Biol Med 1975; 149: 5702.
  • 44
    Compston JE, Creamer B. Plasma levels and intestinal absorption of 25-hydroxyvitamin D in patients with small bowel resection. Gut 1977; 18: 1715.
  • 45
    Tajika M, Matsuura A, Nakamura T, et al. Risk factors for vitamin D deficiency in patients with Crohn's disease. J Gastroenterol 2004; 39: 52733.
  • 46
    Geerling BJ, Badart-Smook A, Stockbrugger RW, Brummer RJ. Comprehensive nutritional status in patients with long-standing Crohn's disease currently in remission. Am J Clin Nutr 1998; 67: 91926.
  • 47
    Lo CW, Paris PW, Clemens TL, Nolan J, Holick MF. Vitamin D absorption in healthy subjects and in patients with intestinal malabsorption syndromes. Am J Clin Nutr 1985; 42: 6449.
  • 48
    Freaney R, McBrinn Y, McKenna MJ. Secondary hyperparathyroidism in elderly people: combined effect of renal insufficiency and vitamin D deficiency. Am J Clin Nutr 1993; 58: 18791.
  • 49
    Brot C, Jorgensen NR, Sorensen OH. The influence of smoking on vitamin D status and calcium metabolism. Eur J Clin Nutr 1999; 53: 9206.
  • 50
    Wortsman J, Matsuoka LY, Chen TC, Lu Z, Holick MF. Decreased bioavailability of vitamin D in obesity. Am J Clin Nutr 2000; 72: 6903.
  • 51
    McCarthy DA. Seasonal variation in serum vitamin D and parathyroid hormone levels in Irish population subgroups. MSc thesis. Cork, Ireland: National University of Ireland, 2004.
  • 52
    Bernstein CN, Bector S, Leslie WD. Lack of relationship of calcium and vitamin D intake to bone mineral density in premenopausal women with inflammatory bowel disease. Am J Gastroenterol 2003; 98: 246873.
    Direct Link:
  • 53
    Bernstein CN, Seeger LL, Anton PA, et al. A randomized, placebo-controlled trial of calcium supplementation for decreased bone density in corticosteroid-using patients with inflammatory bowel disease: a pilot study. Aliment Pharmacol Ther 1996; 10: 77786.
  • 54
    Reed CA, Nichols DL, Bonnick SL, DiMarco NM. Bone mineral density and dietary intake in patients with Crohn's disease. J Clin Densitom 1998; 1: 3340.
  • 55
    Kiely M, Flynn A, Harrington KE, et al. The efficacy and safety of nutritional supplement use in a representative sample of adults in the North/South Ireland Food Consumption Survey. Public Health Nutr 2001; 4: 108997.
  • 56
    Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr 1999; 69: 84256.
  • 57
    Storm D, Eslin R, Porter ES, et al. Calcium supplementation prevents seasonal bone loss and changes in biochemical markers of bone turnover in elderly New England women: a randomized placebo-controlled trial. J Clin Endocrinol Metab 1998; 83: 381725.
  • 58
    Yonei T, Hagino H, Katagiri H, Kishimoto H. Bone metabolic changes in Antarctic wintering team members. Bone 1999; 24: 14550.
  • 59
    Woitge HW, Knothe A, Witte K, et al. Circaannual rhythms and interactions of vitamin D metabolites, parathyroid hormone, and biochemical markers of skeletal homeostasis: a prospective study . J Bone Miner Res 2000; 15: 244350.
  • 60
    Carnevale V, Modoni S, Pileri M, et al. Longitudinal evaluation of vitamin D status in healthy subjects from southern Italy: aeasonal and gender differences. Osteoporos Int 2001; 12: 102630.
  • 61
    Meier C, Woitge HW, Witte K, Lemmer B, Seibel MJ. Supplementation with oral vitamin D3 and calcium during winter prevents seasonal bone loss: a randomized controlled open-label prospective trial. J Bone Miner Res 2004; 19: 122130.
  • 62
    Rosen CJ, Morrison A, Zhou H, et al. Elderly women in northern New England exhibit seasonal changes in bone mineral density and calciotropic hormones. Bone Miner 1994; 25: 8392.
  • 63
    Patel R, Collins D, Bullock S, Swaminathan R, Blake GM, Fogelman I. The effect of season and vitamin D supplementation on bone mineral density in healthy women: a double-masked crossover study. Osteoporos Int 2001; 12: 31925.
  • 64
    Blumsohn A, Naylor KE, Timm W, Eagleton AC, Hannon RA, Eastell R. Absence of marked seasonal change in bone turnover: a longitudinal and multicenter cross-sectional study. J Bone Miner Res 2003; 18: 127481.
  • 65
    Seibel MJ, Meier C, Woitge H, Witte K, Lemmer B. Seasonal variation of bone turnover? J Bone Miner Res 2004; 19: 1689.
    Direct Link: