Many scientists have set out to understand how vitamin D deficiency and supplementation may influence disease. According to the World Health Organization (WHO), there is some evidence that vitamin D may help protect against respiratory tract infections, for example.
Two other areas of particular interest are vitamin D’s potential effects on cardiovascular disease and cancer risk. However, few RCTs have looked into this. These types of studies are the gold standard for identifying causal relationships in scientific research.
Speaking with Medical News Today, Vimal Karani, a professor of nutrigenetics and nutrigenomics at the University of Reading, in the United Kingdom, confirmed that there has been a gap between the initial research and findings from clinical trials.
A recent study, which appears in The American Journal of Clinical Nutrition, goes some way toward addressing this knowledge gap.
Vitamin D helps the body absorb calcium, which improves bone strength. Among other roles, it also contributes to the functioning of muscles, nerves, and the immune system.
Over the past 2 years, researchers have also explored whether vitamin D reduces the risks associated with COVID-19. Although investigations are ongoing, there seems to be some evidence that these supplements might improve intensive care unit admission rates.
Prof. Karani was not involved in the recent study but has worked with some of its authors.
He explained that past large epidemiological studies “have established a link between vitamin D deficiency and the risk of [cardiovascular disease] traits in various ethnic groups.” This, he said, suggests that vitamin D supplements might lower cardiovascular risk.
“However,” he continued, “clinical trials have not provided convincing evidence of the blood pressure-lowering effect of vitamin D supplementation.” Prof. Karani said that there could be a wide range of reasons for this, including “differences in the sample size, duration of supplementation, dose of the supplementation, age of the participants, geographical location, sun exposure, and the outcome measures. Further research is required to replicate the findings in multiple ethnic groups.”
To provide further evidence of the relationship between vitamin D, cardiovascular disease, and cancer, the researchers behind the present study conducted the Finnish Vitamin D Trial. This took place between 2012 and 2018, and it was double-blind, randomized, and placebo-controlled.
“When we started to plan the trial, there was a lot of evidence from observational studies that vitamin D deficiency would be associated with nearly all major chronic diseases, such as [cardiovascular disease], cancer, type 2 diabetes, and also mortality,” said Dr. Jyrki Virtanen in an interview with Medical News Today. Dr. Virtanen is an associate professor of nutrition and public health at the University of Eastern Finland, and a co-principal investigator of the study.
“Therefore, our aim was to start a long-term vitamin D supplementation trial in Finland, where vitamin D insufficiency had been quite prevalent due to the long winter, and investigate whether vitamin D supplementation could reduce the risk of major chronic diseases and death.” The researchers looked at data from 2,495 people, including male participants 60 years or older and female participants who were postmenopausal and 65 years or older. The participants also had no history of cardiovascular disease or cancer.
“At that time, there was little evidence from RCTs that improvement of [the] vitamin D status of the body with vitamin D supplementation reduced the risk of diseases.” “Also, we had shown that among [the] Eastern Finnish population, low vitamin D content of the body was associated with higher risk of mortality and glucose metabolism disturbances. However, these kinds of studies do not give evidence for causality.”