Vitamin D Heart Risk Mediated by Race

The risk of coronary heart disease associated with low serum levels of 25-hydroxyvitamin D (25[OH]D) varies by race and ethnicity, researchers found.

Both whites and patients with Chinese ancestry had a significantly increased risk of coronary heart disease with a 10-ng/mL decrease in 25(OH)D levels (HR 1.26, 95% CI 1.06-1.49 and HR 1.67, 95% CI 1.07-2.61, respectively), according to Ian de Boer, MD, of the University of Washington in Seattle, and colleagues.

But that relationship wasn't observed among blacks (HR 0.93, 95% CI 0.73-1.20) and Hispanics (HR 1.01, 95% CI 0.77-1.33), the investigators reported in the July 10 issue of the Journal of the American Medical Association.

'Our study suggests that the risks and benefits of vitamin D supplementation should be evaluated carefully across race and ethnicity, and that the results of ongoing vitamin D clinical trials should be applied cautiously to individuals who are not white,' they wrote.

The lack of an association in blacks was unexpected because they had the lowest 25(OH)D levels at baseline, said Keith Norris, MD, of the University of California Los Angeles, who co-wrote an accompanying editorial with Sandra Williams, DMD, MD, of the Cleveland Clinic Florida in Weston.

It could be, Norris said in an interview, that sustained low vitamin D concentrations induce adaptations over time such that the body is not as susceptible to the effects or that the heavier burden of cardiovascular risk factors among minority groups masks any potentially detrimental effects of low vitamin D levels.

The study 'reinforces what we're seeing in medicine, [which] is a push toward personalized medicine where we're really looking beyond what happens to a whole group of people, but how do we understand what's happening at more [of] an individual level,' Norris said.

Previous studies that have shown a relationship between low levels of vitamin D and an increased risk of coronary heart disease have included mostly white participants, and the issue has not been as well studied in other racial or ethnic groups, who may have differences in vitamin D metabolism and circulating levels of 25(OH)D.

De Boer and colleagues explored the issue using data from the Multi-Ethnic Study of Atherosclerosis (MESA), which recruited individuals ages 45 to 84 from six sites around the country. The current analysis included 6,436 participants (mean age 62; 53% female) who were free from known cardiovascular disease and had 25(OH)D levels measured at baseline.

The participants were 38% white, 28% black, 22% Hispanic, and 12% of Chinese ancestry. The average 25(OH)D concentrations in each group at baseline were 30.1, 19.2, 24.6, and 26.7 ng/mL, respectively.

During a median follow-up of 8.5 years, there were 361 incident coronary heart disease events, a composite of MI, definite or probable angina, cardiac arrest, or coronary heart disease death.

In the overall study population, each 10-ng/mL decrease in 25(OH)D was associated with an elevated risk of events after adjustment for numerous potential confounders (HR 1.15, 95% CI 1.01-1.32), although the risk differed significantly among the racial/ethnic groups ( P<0.05 for the interaction).

De Boer and colleagues said the data point to biological differences to explain the finding.

'In white populations, low 25(OH)D may lead to 1,25 dihydroxyvitamin D deficiency with resulting inappropriate activation of the renin-angiotensin system, dysregulation of immune cell functions, and failure to inhibit abnormal cell proliferation,' they wrote. 'Differences in vitamin D metabolism may interrupt this sequence in black populations.'

The researchers advised caution in interpreting the results in the Chinese and Hispanic participants because of the low sample sizes.

They acknowledged some additional limitations of the study, including potential residual confounding, limited power to find small associations within each racial/ethnic subgroup, and the use of a single 25(OH)D measurement taken at baseline.

The study was supported by grants from the National Heart, Lung and Blood Institute.

De Boer reported receiving grant funding from the NIH and Abbott Laboratories. His co-authors reported relationships with the NIH and Amgen.

Norris reported receiving grant support from the NIH and payment for lectures and consulting from Abbott, Amgen, DaVita, and Takeda. Williams reported that she had no conflicts of interest.

Title : Vitamin D Heart Risk Mediated by Race
Published on : Thursday, July 11, 2013
Category : Vitamin D
Post URL : http://internal-med.blogspot.com/2013/07/vitamin-d-heart-risk-mediated-by-race.html