Association of C‐reactive protein and vitamin D deficiency with cardiovascular disease: A nationwide cross‐sectional study from National Health and Nutrition Examination Survey 2007 to 2008

Abstract Objectives The association of C‐reactive protein (CRP) and serum 25‐hydroxyvitamin D [25(OH)D] and cardiovascular disease (CVD) remains unknown. Methods We performed a cross‐sectional analysis on 3848 participants by using the data from the National Health and Nutrition Examination Surveys (2007 to 2008). CVD was defined as a compromise of stroke, myocardial infarction, heart failure, and coronary heart disease. High CRP was defined as ≥0.2 mg/dL, and vitamin D status were categorized as severe deficiency, <25 nmol/mL; deficiency, 25 to 49.9 nmol/mL; insufficiency, 50 to 74.9 nmol/mL; and normal, ≥75 nmol/mL. Statistical analysis was performed using logistic regression models. Results We found that both high CRP and low 25(OH)D levels were associated with CVD. Participants with high CRP levels and severe vitamin D deficiency had a higher likelihood of having CVD than those with neither risk factor (odds ratio = 2.69, 95% confidence interval = 1.45‐4.98, P = .0017). In stratified analysis, a significant positive association between vitamin D level and CVD was observed only in the high CRP group. However, in the absence of high CRP, even with severe vitamin D deficiency, no association was found with an increasing risk of CVD (P = .6416). Conclusion Within a cross‐sectional, nationally representative sample, these findings suggest that vitamin D status evaluation, or vitamin D supplement may be especially important for individuals with high CRP levels.


| Serum 25(OH)D and CRP concentration
(50-74.9 nmol/mL), deficient (25-49.9 nmol/mL), and severely deficient (<25 nmol/mL). 23,24 Serum CRP was measured as described in the NHANES Laboratory Procedures Manual. CRP was measured using latex-enhanced nephelometry (Dade Behring Diagnostics Inc., Somerville, New Jersey), with high CRP levels defined as 0.20 mg/dL or greater. This process was then repeated substituting vitamin D deficiency for severe vitamin D deficiency referred to previous literature. 25

| Covariates
We chose covariates as potential confounding factors based on prior studies or based on their biological plausibility. The following covariates were included in our association analysis: age, sex, race/ethnicity, body mass index (BMI), family poverty income ratio (PIR), marital status, educational level, smoking status, alcohol consumption, physical activity, hypertension, diabetes, hypercholesterolemia, chronic kidney disease (CKD), and season of blood collection. Race/ethnicity was classified as non-Hispanic white, non-Hispanic black, Mexican American, and other. Marital status was classified as single/never married, married/live together, widowed, separated/divorced, and others. We categorized educational level as less than a high school education/primary education, a high school education/secondary education, and a college education. BMI was calculated as weight in kilograms divided by height in meters squared (kg/m 2 ). Height and weight were collected in the mobile examination center. The self-reported PIR, a marker of socioeconomic status used in multiple prior studies. 26 Smoking status was classified as never, former, or current, which was constructed from responses to two questions: "Have you smoked at least 100 cigarettes in your life?" and "Do you now smoke cigarettes?" Participants who reported smoking every day or some days and had smoked at least 100 cigarettes were categorized as current smokers; respondents who reported currently not smoking but having smoked more than 100 cigarettes in the past were categorized as former smokers; and respondents who reported having smoked fewer than 100 cigarettes ever were categorized as non-smokers. 27 Alcohol consumption was defined as having at least 12 drinks of any type of alcoholic beverage in the past year. 28 Table 1. The percentage of subjects with CVD was higher in those with lower levels of vitamin D, yet this did not reach a statistically significant (P = .887). Participants with CVD had a significantly greater frequency of high CRP than those without (64.06% vs 50.10%; P < .001).
On average, individuals with CVD were more likely to be older, male, non-Hispanic black, a former smoker, less educated, and less physically active than participants without CVD. Moreover, they had higher BMI, lower family PIR; they were less likely to be married and non-smokers, and had more traditional CVD risk factors, such as hypertension, diabetes mellitus, hypercholesterolemia, and CKD (Table 1).  We then evaluated the association between vitamin D and CVD based on high or low CRP level. The ORs for CVD associated with 25(OH)D level are listed in Table 4 and were different between different CPR level status (high or low). We observed a significant association between vitamin D level and CVD only in the high CRP group, but not in the low CRP group across all three logistic regression models. In subjects with high CRP, the OR of having CVD was 2.43 (95% CI = 1.23-4.82, P = .0110) in individuals who also exhibited severe vitamin D deficiency compared with those with normal vitamin D levels. Those with lower 25(OH)D levels were more likely to have had a CVD outcome, and was dependent of CRP status (Table 4).

| DISCUSSION
In the present study, we performed a large cross-sectional study of nationally representative sample of adults >20 years of age by using continuous NHANES (2007)(2008). In addition to being a disease of modified lipoproteins accumulation in the artery wall, inflammation is also an additional key aspect of this disease process. 32 In this study, we chose CRP as such a marker of inflammation, and confirmed that individuals with high CRP had a higher likelihood of CVD (Table 2).
Lower vitamin D status was previously found to be associated with increased risk and unfavorable outcome of CVD, 33,34 herein, our results revealed that individuals with both high CRP and severe vitamin D deficiency had 2.69 times the likelihood for experiencing CVD, which was higher than those with neither of them (Table 3). In terms of clinical application, the addition of the measurement of CRP to screening based on vitamin D levels may thus provide a simple and inexpensive method to improve risk prediction for cardiovascular events.
In the stratified analysis of the current study, we found that in the absence of inflammation, even having severe vitamin D deficiency was not associated with increasing likelihood of CVD, but participants with high CRP without severe vitamin D deficiency were still more likely to have CVD ( Abbreviations: CI, confidence interval; CRP, C-reactive protein; OR, odds ratio. Model 1: adjusted for age, gender, and race at baseline. Model 2: adjusted for variables in model 1 and physical activity, educational level, marital status, family poverty income ratio, body mass index, season of blood collection, smoking status, and alcohol drinking. Model 3: adjusted for variables in model 2 and hypertension, diabetes mellitus, hypercholesterolemia, history of chronic kidney desease.