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Keywords:

  • allergic rhinitis;
  • confounder;
  • sensitization;
  • vitamin D

Abstract

  1. Top of page
  2. Abstract
  3. Background
  4. Study participants, materials and methods
  5. Results
  6. Conclusions
  7. References

In addition to its role in the regulation of calcium metabolism, vitamin D has a number of immunological effects. Several studies in children found an effect of oral supplementation on allergic sensitization but so far there are no population-based studies of vitamin D serum levels. We therefore examined 25(OH)-D3 status in 18 224 adults of the Third National Health and Nutrition Examination Survey. There was no effect on sensitization to a single allergen while the prevalence of allergic rhinitis increased across quartile groups of current vitamin D serum levels. The association could be due to unrecognized confounding, however, could also point towards an altered metabolism or an increased sensitivity to vitamin D in allergic patients.


Background

  1. Top of page
  2. Abstract
  3. Background
  4. Study participants, materials and methods
  5. Results
  6. Conclusions
  7. References

In addition to its essential role in the regulation of calcium metabolism, vitamin D is known to have a number of immunological effects (1). This was the reason that we speculated about an association of early rickets prophylaxis effect and induction of allergic sensitization (2). This hypothesis has gained wider attention by a number of recent epidemiological studies (3–7) that all showed an association under quite heterogeneous conditions. We have now analysed the association between serum 25(OH)-D3 levels and allergy in adults using the Third National Health and Nutrition Examination Survey (NHANES III) study (8).

Study participants, materials and methods

  1. Top of page
  2. Abstract
  3. Background
  4. Study participants, materials and methods
  5. Results
  6. Conclusions
  7. References

The NHANES are conducted by the National Center for Health Statistics, Centers for Disease Control (NCHS/CDC) and designed to assess the health and nutritional status of adults and children in the United States through interviews and direct physical examinations using specially equipped mobile examination centres. The public available data set of the NHANES III, 1988–1994, data release series 11, No. 2A, April 1998, was accessed in October 2003 and again February 2007. Only participants with non-Hispanic White or African-American ethnic background, known age and level of 25(OH)-D3 status were included (n = 18 224). As it is known that 25(OH)-D3 serum levels are lower in people of African-American descent and higher at younger ages, the analysis of 25(OH)-D3 serum levels was stratified for ethnic origin and age.

Hayfever was defined by the question ‘Did a doctor ever tell you had hay fever’, frequency of symptoms by ‘Number of episodes itchy … nose/eyes in the past 12 months’ and asthma by the question ‘Did a doctor ever tell you had asthma’. Allergen sensitization was defined by an absolute skin wheal length of ≥ 3 mm in response to an applied allergen (9).

Results

  1. Top of page
  2. Abstract
  3. Background
  4. Study participants, materials and methods
  5. Results
  6. Conclusions
  7. References

Allergic rhinitis increased with levels of 25(OH)-D3 in all subgroups (Table 1) while additional adjustment for sex, geographical region and month of examination did not change this association. The risk was the most prominent in the young, the white group also had the highest absolute vitamin D values. Furthermore, the number of allergic episodes was correlated with vitamin D levels (Table 1). Sensitization to any specific allergens tested was not consistently altered by the current vitamin D levels (data not presented) possibly as the high sensitization rate of nearly half of the population affected may have masked effects. Unfortunately, serum immunoglobulin E levels were not available in this study.

Table 1.   Vitamin D status and prevalence of allergic rhinitis by ethnic group
Ethnic backgroundAge group (years) 25(OH)-D3 quartile level (nM)Diagnosis allergic rhinitis cases (N )Percentage with diagnosis allergic rhinitis of totalOR 95% confidence limitsP-valueAverage number of episodes last yearP-value*
  1. *Based on a log–log linear regression model.

White, non-Hispanic≤200.042.51.00Reference 26.8 
61.2225.52.250.76–6.640.141241.5 
80.4457.53.121.11–8.810.031638.3 
400649.54.051.45–11.280.007656.70.0298
> 200.01578.41.00Reference 86.6 
61.22047.80.920.74–1.150.476174.4 
80.42759.11.090.89–1.340.403974.9 
40034810.41.251.03–1.530.024578.70.0111
African-American≤200.0265.51.00Reference 32.2 
61.2257.81.460.82–2.570.195653.3 
80.4187.61.420.76–2.650.266934.5 
4001410.62.041.04–4.040.039538.40.1993
> 200.01888.81.00Reference 54.4 
61.212310.11.160.91–1.470.228558.6 
80.46810.21.170.87–1.570.290246.0 
400369.41.070.74–1.560.705857.10.9439

Conclusions

  1. Top of page
  2. Abstract
  3. Background
  4. Study participants, materials and methods
  5. Results
  6. Conclusions
  7. References

An increase in the prevalence of allergic rhinitis with vitamin D levels could be observed at all ages with more prominent effects in children probably indicating a higher relevance at an earlier disease stage. Unrecognized confounding may be one reason for the observed association, but seems unlikely from earlier experimental, clinical and epidemiological studies (3–7). Reverse causation, e.g. summer outdoor exposure to sun and higher allergen concentration, are also unlikely as adjustment for the month of examination did not alter the association. These results may therefore indicate subtle differences in vitamin D metabolism or sensitivity in allergic patients.

References

  1. Top of page
  2. Abstract
  3. Background
  4. Study participants, materials and methods
  5. Results
  6. Conclusions
  7. References
  • 1
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  • 8
    Nesby-O’Dell S, Scanlon KS, Cogswell ME, Gillespie C, Hollis BW, Looker AC et al. Hypovitaminosis D prevalence and determinants among African American and white women of reproductive age: third National Health and Nutrition Examination Survey, 1988-1994. Am J Clin Nutr 2002;76:187192.
  • 9
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