Vitamin D: Too Much May Erase Heart Benefit

Muhammad Amer, MD, and Rehan Qayyum, MD, MHS, from Johns Hopkins University School of Medicine reported that, the critical threshold appears to be a serum 25-hydroxyvitamin D concentration of 21 ng/mL -- more than that level increases C-reactive protein (CRP), a biomarker for cardiovascular disease, but lower serum concentrations of 25-hydroxyvitamin D lower CRP levels.

A multivariate analysis that tracked 25-hydroxyvitamin D concentrations as well as CRP in more than 15,000 healthy adults revealed that above the threshold for benefit, CRP increased with each 10-ng/mL increase in 25-hydroxyvitamin D.

In a univariate analysis, CRP levels decreased as levels of 25-hydroxyvitamin D increased up to the median of 2 ng/mL.

The authors analyzed data from participants in the National Health and Nutrition Examination Survey (NHANES). Researchers combined three two-year cycles of continuous NHANES surveys from 2001 to 2006.

The mean age of participants was 46, and the median serum 25-hydroxyvitamin D and CRP levels were 21 ng/mL and 0.21 mg/dL, respectively. The proportion of men to women was close, 48% versus 52%, with no significant difference in levels of 25-hydroxyvitamin D between the two groups.

Whites had significantly higher baseline levels of 25-hydroxyvitamin D than nonwhites.

Significantly more people with a body mass index greater than 30 kg/m² had lower 25-hydroxyvitamin D levels at baseline (41% versus 25%, P<0.0001); the same was true for smokers (22% versus 18%, P=0.004).

However, the mean total cholesterol was significantly higher for those with higher levels of vitamin D at baseline (201.6 versus 198.6 mg/dL, P=0.001).

"From our results, it appears that vitamin D supplementation among asymptomatic subjects with baseline vitamin D values of greater than 21 ng/mL might have no additional effects on systemic inflammation, as measured by changes in the serum CRP levels," Amer and Qayyum concluded.

Researchers admitted they could not determine a temporal relation between 25-hydroxyvitamin D and CRP. Another limitation was the inability to adjust for geographic location or time of year.

• Point out that this study found a significant inverse relationship between CRP and 25-hydroxyvitamin D levels less than 21 ng/mL.
• Note that prior studies assessing the relationship between vitamin D status and markers of inflammation have yielded inconsistent results.

Amer M, Qayyum, R "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" Am J Cardiol 2012; 109: 226–230