Cardiovascular disease (CVD) refers to a wide range of conditions affecting the heart and blood vessels such as veins and arteries. It is the leading cause of death and is also responsible for a high disability rate worldwide. Efforts have been made to research and identify risk factors for atherosclerosis, the hardening and potential blockage of arteries, which is considered the main cause for CVD.
The main measures of CVD are lipid levels in the blood. These include: total cholesterol, high density lipoprotein cholesterol (HDL-C) “good or ‘highly desired’ cholesterol”, low density lipoprotein cholesterol (LDL-C) “bad or ‘least desired’ cholesterol”, and triglycerides (TGs) a type of fat that is found in the bloodstream and other tissues. Many observational studies have identified a relationship between low levels of vitamin D in the blood and increased risk of CVD and a bad lipid profile. On the other hand, high levels of 25-hydroxy-vitamin D (the form that is measured in the blood) is associated with a positive lipid profile. Since this information was never formally studied in a clinical trial, there is no conclusive evidence for cause and effect that it was in fact vitamin-D levels that improved lipid profiles.
12 experimental studies, with a total of 1,346 persons, ages 18-80 involved, were analyzed for the purpose of this study.
Out of 1,384 articles that were found, the researchers selected 12 intervention studies using vitamin D supplementation that were double blind randomized control trials. In other words, the subjects involved in the study were randomly placed in groups that were either treated with a vitamin D or placebo supplement (that has no vitamin D). Neither the subjects nor those administering the supplements knew in which group they were placed.
Surprisingly, supplementation of vitamin D resulted in a significant increase in LDL-C. Additionally, there was an insignificant trend towards increase in total cholesterol, reduction in HDL-C, and reduction of TG levels. The effect of vitamin D supplements on LDL-C was found to be more significant in obese people and in studies that lasted over a shorter time period. Studies for longer durations resulted in some significant reduction in levels of HDL-C.
Relatively few studies met the criteria for the analysis, and none of them studied a large sample of subjects. Most participants were non-Hispanic, white, and elderly, reducing the ability to apply the findings to these populations. The studies also varied in dose, form and duration of vitamin D supplementation. Finally, none of the studies were specifically intended to evaluate the impact of vitamin D supplementation on the levels of lipids in the blood.
While there are findings that higher blood vitamin D levels will reduce the risk of CVD, the change in lipid levels are not in the direction expected. Vitamin D supplementation influences blood lipid concentrations, but none of the studies were designed to study this outcome. A study designed to examine blood lipids should be done to understand the role, if any, of vitamin D supplementation as a preventative measure for CVD.
The full report is titled “Influence of vitamin D supplementation on plasma lipid profiles: A meta-analysis of randomized controlled trials.” Lipids in Health and Disease, 2012: 11:42. The authors are Wang H, Xia, N, Yang Y, Peng DQ.
Written by Mashie Shirken and Melissa Nutini, Dept. Nutritional Sciences, Rutgers University-NewBrunswick Edited by SA Shapses, PhD, RD