Epidemiological studies have shown that people with low levels of vitamin D are more susceptible to various cancers. What can you do to reverse your risk? The answer is not clear. We do not know if taking vitamin D pills to increase blood levels will lower your chance of cancer. Randomized controlled trials of vitamin D supplements have provided inconsistent results.
High-Dose Vitamin D Did Not Lower the Chance of Cancer:
The latest trial is from New Zealand (JAMA Oncology, online July 19, 2018). More than 5,000 people were randomly assigned to take vitamin D capsules or identical-appearing placebo capsules. Everyone in the study took a pill once a month for about four years. Each monthly dose was 100,000 IU of vitamin D3.
During the study, 400 participants developed cancer or died as a result of cancer complications. These people were in both in the vitamin D group and the placebo group. As a result, vitamin D pills don’t seem to have changed their chance of cancer diagnosis.
The investigators suggest that
“monthly high-dose vitamin D supplementation is not associated with reductions in cancer incidence or cancer mortality…”
Such big doses of vitamin D once a month do not reflect the body’s natural way of daily incremental dosing from the sun. Whether a different dosing schedule would have a different outcome remains to be determined. We will be watching for future studies with more physiologically normal dosing patterns to see if any of them can reduce the chance of cancer.
You can find out more about sources, doses and benefits of vitamin D in our Guide to Vitamin D Deficiency.