The health benefits of vitamin D supplementation are still unclear in research. For example, some studies have found that this fat-soluble vitamin is associated with better cognitive function. In contrast, other research has found no links between vitamin D supplementation and a lower risk of cardiovascular disease or cancer.
A systematic review and meta-analysis published in the Annals of Internal Medicine suggests that supplementing with vitamin D may lower the risk of diabetes in people with prediabetes. However, an editorial accompanying the research points out that although vitamin D may reduce diabetes risk in some people, high-dose vitamin D therapy could cause harm.
Scientists from Tufts Medical Center examined three randomized trials looking at whether supplementing with vitamin D affected diabetes risk in people with prediabetes. They found that during a three-year follow-up period, vitamin D reduced the risk for diabetes by 15%. In addition, participants who had vitamin D serum levels of at least 125 nmol/L had a 76% lower risk of diabetes compared to people with serum levels of 50–74 nmol/L.
According to a news release, the study authors say that generalizing their findings to the more than 374 million adults worldwide with prediabetes, suggests that vitamin D supplementation could potentially delay the onset of diabetes in more than 10 million people.
However, the study only examined the impact of vitamin D on people with prediabetes, so the findings might not apply to the general population. Moreover, an accompanying editorial by authors from the Food Safety Authority of Ireland and the University College Dublin suggests that healthy adults may take more vitamin D than is required for health and wellbeing. And this overdosing could cause harm in some cases.
They also note that vitamin D supplementation in healthy individuals is best determined by looking at total vitamin D intake from all sources, including natural foods, fortified foods, and sun exposure. In addition, healthcare providers can evaluate an individual’s vitamin D status with a blood test that measures serum 25-hydroxyvitamin D (25-[OH]D) concentration.