Jan. 2020
In recent years, some studies have shown that low blood vitamin D levels are associated with increased risks of cancer, cardiovascular disease and type 2 diabetes. These findings have prompted proposals to use vitamin D supplements to decrease the risks of these diseases.
However, the results of two large well-designed randomized clinical trials published in the New England Journal of Medicine (Jan. 3, 2019 and Aug. 8, 2019) demonstrated that high dose vitamin D supplementation was not useful for preventing invasive cancer of the breast, prostate and colon/rectum or of major cardiovascular events. Furthermore, there was no protection for death from cancer or death from any cause.
Official US nutritional guidelines recommend that healthy adults up to age 70 consume 600 international units (IU) of vitamin D daily. After age 70, the recommended daily allowance increases to 800 IU.
Cancer and Cardiovascular Disease Prevention Trial
Over 25,000 healthy adults all over age 50 were random assigned to receive either oral vitamin D at a high dose of 2,000 IUs or a placebo once daily. With a follow-up of 5 years, the researchers could not find any statistically significant differences between the vitamin D and placebo groups in their rates of invasive cancer of any type or of major cardiovascular disease events.
Diabetes Prevention Trial
In the second study, 2,243 adults at high risk for diabetes (pre-diabetics) were randomly assigned to receive either oral vitamin D at a high dose of 4,000 IUs or a placebo once daily. With a follow-up of 2.5 years, the researchers could not find any statistically significant difference in the rate of new-onset diabetes between the vitamin D and placebo groups.
Conclusion
These trials showed that high doses of vitamin D supplements taken in an effort to reduce the risks of cancer, cardiovascular disease or type diabetes are not protective.