Pooling data from 52 trials – which totaled 75,454 participants – indicated that vitamin D supplementation was not associated with a reduction in so-called “all cause mortality”, but it was associated with a statistically significantly reduced the risk of cancer death.
Writing in the British Medical Journal scientists from China and the US report that the effects were more pronounced for vitamin D3 vs D2 supplementation.
“The current study found that all cause mortality was significantly lower among trials with vitamin D3 supplementation than in trials with vitamin D2 supplementation, with a trend towards reduced all cause mortality in those taking vitamin D3 (P=0.06),” they wrote.
“Similarly, vitamin D3 supplementation reduced the risk of cancer death, but vitamin D2 did not.
“Another finding from subgroup analysis suggested that all cause mortality was significantly lower in trials with longer follow-up, and that the benefit of reduced cancer mortality was seen in trials with longer follow-up (more than three years) but not in those with a shorter follow-up. According to these findings, supplementation with vitamin D3 for at least three years should be considered,” they added.
Vitamin D and cancer
The potential anti-cancer effects of vitamin D have been reported many times over the years, although the overall data is conflicting. The link was first proposed in 1941 when Frank Apperly demonstrated a link between latitude and deaths from cancer, and suggested that sunlight gave "a relative cancer immunity".
Since then there have been numerous studies suggesting associations between vitamin D and lower risks of certain cancers.
Commenting on the new study, Andrea Wong, Ph.D., vice president, scientific & regulatory affairs at the Council for Responsible Nutrition, called the new findings “promising” but called for more research into the topic.
“Scientific evidence demonstrating the benefits of vitamin D continues to grow, and this new research, which finds an association between vitamin D supplementation and reduced risk of cancer death, is no exception,” said Dr Wong. “CRN considers the newest findings to be promising, and we strongly encourage further investigations into the association between vitamin D and this particular outcome.
“Cancer is complex and multifactorial. Taking a long-term, comprehensive approach in consultation with a healthcare practitioner is what contributes the most to disease prevention. Optimal nutrition is only one component of many.”
Study details
The China and US-based scientists set out to investigate if there was a relationship between vitamin D supplementation and mortality in adults.
Data from 52 trials qualified for inclusion in their analysis, which revealed that while vitamin D supplementation over all was not associated with all-cause mortality risk, a significant reduction in cancer death risk was observed. Further analysis revealed that this was only seen for vitamin D3 supplementation, and not D2 supplementation.
The researchers called for additional large clinical studies to further investigate these relationships, but noted that three ongoing trials have the potential to corroborate or refute the findings, including the D-Health trial (Australia), the VIDAL (Vitamin D and Longevity) trial (UK), and the DO-HEALTH (Vitamin D3-Omega3-Home Exercise-Healthy Ageing and Longevity) trial.
“Although none of these trials have screened for low baseline 25 hydroxyvitamin D for eligibility, all trials have used vitamin D3 as the intervention,” noted the researchers.
The sunshine vitamin
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D).
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
Vitamin D: A nutrient of public health concern
CRN’s Dr Wong added that, “everyone, at any life stage, has a nutritional need for vitamin D. It is an essential nutrient, critical to overall health, and yet most people do not get enough, which is why the most recent Dietary Guidelines identified vitamin D as a nutrient of public health concern.
“Additionally, the prevalence of vitamin D shortfalls—and the adverse health outcomes affiliated with under-consumption of this nutrient—is why so many healthcare practitioners recommend their patients take a vitamin D supplement.”
“Taking vitamin D supplements is a safe and appropriate way to achieve healthy levels, especially because vitamin D is not easily obtained through food alone,” she said. “CRN encourages consumers to have their serum vitamin D levels checked, and to consult with their doctor or other healthcare practitioner about the role supplementation plays in their overall health and wellness regimen.”
Source: British Medical Journal
2019; 366, doi: 10.1136/bmj.l4673
“Association between vitamin D supplementation and mortality: systematic review and meta-analysis”
Authors: Y. Zhang et al.