Preventive cardiology
Relation Between Serum 25-Hydroxyvitamin D and C-Reactive Protein in Asymptomatic Adults (From the Continuous National Health and Nutrition Examination Survey 2001 to 2006)

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The inverse relation between vitamin D supplementation and inflammatory biomarkers among asymptomatic adults is not settled. We hypothesized that the inverse relation is present only at lower levels and disappears at higher serum levels of vitamin D. We examined the relation between 25-hydroxyvitamin D [25(OH)D] and C-reactive protein (CRP) using the continuous National Health and Nutrition Examination Survey data from 2001 to 2006. Linear spline [single knot at median serum levels of 25(OH)D] regression models were used. The median serum 25(OH)D and CRP level was 21 ng/ml (interquartile range 15 to 27) and 0.21 mg/dl (interquartile range 0.08 to 0.5), respectively. On univariate linear regression analysis, CRP decreased [geometric mean CRP change 0.285 mg/dl for each 10-ng/ml change in 25(OH)D, 95% confidence interval [CI] −0.33 to −0.23] as 25(OH)D increased ≤21 ng/ml. However, an increase in 25(OH)D to >21 ng/ml was not associated with any significant decrease [geometric mean CRP change 0.05 mg/dl for each 10-ng/ml change in 25(OH)D, 95% CI −0.11 to 0.005) in CRP. The inverse relation between 25(OH)D below its median and CRP remained significant [geometric mean CRP change 0.11 mg/dl for each 10-ng/ml change in 25(OH)D, 95% CI 0.16 to −0.04] on multivariate linear regression analysis. Additionally, we observed a positive relation between 25(OH)D above its median and CRP [geometric mean CRP change 0.06 mg/dl for each 10-ng/ml change in 25(OH)D, 95% CI 0.02 to 0.11) after adjusting for traditional cardiovascular risk factors. In conclusion, from this cohort of asymptomatic adults, independent of traditional cardiovascular risk factors, we observed a statistically significant inverse relation between 25(OH)D at levels <21 ng/ml and CRP. We found that 25(OH)D at a level ≥21 ng/ml is associated with an increase in serum CRP. It is possible that the role of vitamin D supplementation to reduce inflammation is beneficial only among those with a lower serum 25(OH)D.

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Methods

We used publically available data from the continuous National Health and Nutrition Examination Survey (NHANES), an ongoing, multistage, probability sample survey designed to assess the health and nutritional status of the civilian, noninstitutionalized population of the United States. Detailed interviews, physical examinations, and serum samples were obtained from >17,000 subjects in the survey conducted from 2001 to 2006. Details of sampling procedures and data collection techniques have been

Results

After excluding the participants who were <18 years old, the population size of the continuous NHANES 2001 to 2006 survey was 17,176. We also excluded participants with missing values for vitamin D (n = 1,993) and CRP (n = 16), leaving 15,167 participants in the sample (Table 1). The participants had a mean ± SD age of 46.1 ± 20.4 years, and the median serum 25(OH)D and CRP level was 21 ng/ml (interquartile range 15 to 27) and 0.21 mg/dl (interquartile range 0.08 to 0.5), respectively. In the

Discussion

In the present, large, cross-sectional study of a nationally representative sample of adult United States population, we found an inverse relation between vitamin D and CRP in asymptomatic adults with low vitamin D levels. However, the relation reversed once the vitamin D increased above the population median (i.e., 21 ng/ml), after which any additional increase in vitamin D was not associated with a decrease, but rather an increase, in the CRP levels. Our finding of a direct relation between

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