A new analysis of randomized controlled trials, published in the British Journal of Cancer, has found that vitamin D supplementation may reduce total cancer mortality, but had no effect on total incidence of cancer.
Through various research, vitamin D levels have been shown to affect cancer. Animal studies have shown that the active form of vitamin D, calcitriol, helps reduce tumor growth and development. Over 15 types of cancer have been associated with low sun exposure, such as breast cancer and colorectal cancer.
Despite these purposed links between vitamin D and various cancers, most trials haven’t found consistent results regarding vitamin D supplementation and cancer incidence or mortality. This is because the randomized controlled trials (RCTs) looking at vitamin D and cancer either didn’t have a strong design, or weren’t looking specifically at cancer mortality and incidence.
Recently, Dr. Nana Keum and Dr. Edward Giovannucci conducted a meta-analysis of RCTs to help determine how vitamin D supplementation affects total cancer mortality and incidence.
The researchers only included RCTs that looked at cancer mortality and incidence. In total, they examined four randomized controlled trials on vitamin D supplementation and total cancer incidence, and three randomized controlled trials on vitamin D supplementation and total cancer mortality.
The length of the randomized controlled trials ranged from two to seven years, with vitamin D doses ranging from 400 to 1100 IU per day.
Their analysis showed the following:
It is important to note that all of the studies but one included calcium as part of their intervention. Since the sample population was replete with calcium, the effect of vitamin D on individuals with low levels of calcium was not determined.
The researchers summarized the implications of their findings,
“In the UK, approximately 159,000 people die of cancer annually, so a 15% reduction would result in a substantial number of potentially preventable deaths from cancer.”
While the results provides substantial evidence that vitamin D supplementation may help reduce total cancer mortality, further randomized controlled trials using adequate dosage should be conducted with total cancer mortality and total cancer incidence as their primary outcomes.