Race against vitamin D – the ‘heart’ of the matter

Vitamin D is one of those crucial vitamins that can impact many areas of your health if you are not getting a sufficient amount. Apart from damage to bone health, vitamin D deficiency has also been implicated in other conditions including heart disease, certain cancers and autoimmune diseases, diabetes, and Alzheimer’s disease. Today we turn our attention to the relationship between vitamin D and heart disease, where a new study looks at how race and ethnicity factors into this equation.

But first, some background: Vitamin D levels are generally different among different ethnic populations. This is because the amount of vitamin D our bodies make from sunlight (ultraviolet B (UVB) rays) depends on how dark or light our skin is – the darker the skin, the lower the amount of UVB the skin takes in. A darker-skinned person therefore makes less vitamin D than a fair-skinned person, even if both of them spend the same amount of time outdoors in the sun and expose the same area of skin.

In general, vitamin D levels are lower in certain ethnic groups with darker skin, such as blacks and Hispanics. Diseases that are linked to low blood vitamin levels D could affect these groups more often than the rest of the population. In order to test this possibility, a group of researchers set out to examine the relationship between low vitamin D levels and risk of heart disease in different ethnic populations.

The researchers analyzed data from 6,436 participants in a large trial and looked to see whether there was any difference in the association between vitamin D and risk of heart disease among white, Chinese, Hispanic, and black participants. None of the participants had heart disease initially. After more than 8 years of follow-up, 361 people had suffered from a heart attack or another heart disease-related event.

Vitamin D for each participant was measured in ng/ml – how many nanograms (1 billionth of a mg) of vitamin D are found in 1 ml of blood. As expected, black participants in the study had the lowest vitamin D levels and Hispanics had the second lowest. When looking at all the participants together as a whole, the researchers found that low vitamin D was linked to heart disease – for every 10ng/ml decrease in vitamin D levels, the risk of heart disease increased by 15%. But when they separated the participants by ethnicity, they discovered a different story. In white and Chinese participants, there was an increased risk of heart disease when vitamin D levels were low. However, in black or Hispanic participants, there was no increase in the risk of heart disease when vitamin D levels were low.

These results are puzzling because if low blood vitamin D indicates greater risk of heart disease, this relationship would show up most prominently in blacks as they had the lowest average blood vitamin D levels in the study. What this study tells us however, is that the relationship between vitamin D and heart disease may not be the same across all racial/ethnic groups. In fact, the results of this study illustrate something that all scientists are generally cautious about, which is that research findings may not be generalizable to all populations. Results can and often do vary with age, gender, and as we have seen in this study, race and ethnicity.

So what to do about vitamin D? Further studies will need to be done to corroborate and confirm these findings. For now, continue to follow your doctor’s instructions and ensure you are getting enough vitamin D. If you are black or Hispanic, your heart may not care if you have low vitamin D, but your bones certainly will! For more information on how much vitamin D you need, follow Osteoporosis Canada’s recommendations.

Reference: Robinson-Cohen C, Hoofnagle AN, Ix JH, et al. Racial differences in the association of serum 25-hydroxyvitamin D concentration with coronary heart disease events. JAMA 2013;310(2):179-88. PMID: 23839752