Fitness gurus, nutrition “experts” and even some physicians are recommending vitamin D supplements for their clients or patients, but a recent study finds that vitamin D may not have the significant benefits claimed. Experts who reviewed more than 260 research studies about vitamin D and its effect on the treatment of various diseases and disorders found no substantial evidence, and the clinical trials were inconclusive, which prevented the experts from reaching any concrete finding. They said that “universal conclusions about its benefits cannot be drawn,” and more vigorous studies are needed to validate most of these health claims.
Vitamin D, also known as the “sunlight vitamin,” is a fat-soluble vitamin that forms in the skin from the sun’s radiation, improving mood and bone structure. It also serves as an antioxidant to prevent cell membrane and DNA damage. Vitamin D comes in two forms: Cholecalciferol (D3) and ergocalciferol (D2). According to Examine, an independent online encyclopedia that offers unbiased sources for supplements and nutrition information and research, vitamin D supplementation is correlated with increased cognition, testosterone levels, and reduced risks of cancer and heart disease. Even with the increasing number of evidence supporting these benefits, they are still being debated and viewed with a skeptical eye.
Two reviews were published in the British Medical Journal in early April. In one review, which was done by a joint team of researchers from Europe and the United States, 107 literature reviews, 74 meta-analyses of observational studies, and 87 meta-analyses of randomized controlled trials on vitamin D were found. Among the 137 different health outcomes that were analyzed, including cardiovascular, metabolic, autoimmune, infectious, bone, and malignant diseases, only ten outcomes had any significant evidence to somewhat confirm any specific benefits. Based on this data, researchers think that there may be some validity between vitamin D intake and concentration with birth weight, maternal health, dental caries in children, and parathyroid hormone concentrations among patients with chronic kidney disease. However, further studies with better trial designs are needed to draw more concrete conclusions.
Also, researchers found that the evidence in the analysis does not support the claim that vitamin D supplementation alone can reduce the risks of falls and fractures in the elderly or increase bone mineral density. There are so many different conclusions in the few hundred studies and meta-analyses that the researchers found that there are no significant roles or benefits of vitamin D supplements for any specific outcome except for a few selected outcomes aforementioned which may be “probable.”
In the second review that was published in the same journal, an international team of researchers led by the Erasmus Medical Centre and the University of Cambridge took a closer look at the extent of vitamin D’s association with deaths from various conditions and circumstances, such as cancer and cardiovascular disease. The researchers analyzed the results of almost 850,000 participants in 73 cohort studies and over 30,700 participants in 22 randomized controlled trials that examined the relationship between vitamin D2 and D3 supplementation and mortality rate.
They found that low levels of vitamin D in the blood were linked to higher risks of mortality from cancer, cardiovascular disease, and other causes when the top third of the sample population in the observational studies were compared to the lower third sample. However, among the randomized controlled trials, there were hardly any significant differences between those who took vitamin D2 supplementation and those who did not. According to their analysis, the average follow-up of the subjects ranged between three to almost seven years. Those participants who took the supplements had a total of 2,527 deaths while the control group had 2,587 deaths. Therefore, this nullified the link between vitamin D2 supplementation and mortality rate. The authors stated that the elderly population are more susceptible to diseases and have a higher risk of death from various causes independent of vitamin D supplementation than younger populations.
For vitamin D3, there may be some benefits. In the 14 trials that examined the relationship between vitamin D3 alone and the risk of death, the mortality rate among all cases were reduced significantly by 11 percent, contrasting that with supplementation of vitamin D2 alone, which “had no overall effect on mortality.”
Even so, the authors of the studies emphasized that “further clinical investigations will be essential to establish the optimal dose, duration and safety, and whether vitamin D2 or D3 have different effects on mortality risk.” In an associated editorial, Dr. Paul Welsh and Dr. Naveed Sattar from the Glasgow University’s British Heart Foundation Research Centre warned that even though vitamin D3 supplementation “seems remarkable,” there are several limitations that must be considered before people start taking vitamin D3 for any reasons.
Welsh and Sattar said that among those 14 vitamin D3 trials, which totaled over 13,600 participants, only six were scored as being at “high risk of bias.” It is also possible that the authors of these studies had drawn different conclusions that were “indicative of inherent uncertainty.” Four of the studies with almost 10,200 participants showed high associations between vitamin D3 intake and fractures in the elderly. However, this does not automatically mean that there is a direct correlation between the two variables because there are other factors independent of vitamin D3 intake that could contribute to the reduced risk of fractures, such as better overall nutrition and exercise. This data also may not apply to middle-aged adults, said Welsh and Sattar.
Some critics of these studies may say that “absence of evidence is not evidence of absence” regarding the current lack of solid evidence that vitamin D has any significant health benefits. Physical therapist Jonathan Fass, DPT, who practices in Riyadh, Saudi Arabia, and works as a sports manager of HRH Prince Alwaleed Bin Talal, disagrees. “Generally, when hundreds of papers have been written and no clear benefit can be found (this assumes that the meta (analysis) was performed well, of course), then we have little reason to suspect that something new will pop up and change the movement of the tides,” Fass stated. “These analyses must be taken seriously, and we must suspect that when we have adequate levels of vitamin D, further supplementation –the kind that has been recommended recently — confers no additional benefit. When this is the case, even the slightest harm — even the financial harm of purchase, or the environmental harm of manufacturing the vitamins — must be considered (since) harm could outweigh the benefit.”
Health care professionals must be cautious when reviewing observational data since there may be errors in interpreting the data and poor experimental setup, while the general public should greet exaggerated claims and anecdotes with some skepticism before forking over their hard-earned money and trust to supplement salespeople. Based on current study findings, Welsh and Sattar suggested that people should not rely on vitamin D supplements as a “protective tablet” for disease prevention and other health benefits since it could lead to a significant false reassurance. A better way to reduce the risk of cancer, cardiovascular disease, and other illnesses is to stick with what is already proven: Better diet, daily exercise, and making better lifestyle changes.
By Nick Ng
Interview with Jonathan Fass