Among healthy postmenopausal women, taking vitamin D and calcium supplements does not appear to lower cancer risk, at least after a period of four years, suggests a trial published last week. The study was published in The Journal of the American Medical Association.
The study supports much of the previous research on the topic, showing no clear link that vitamin D supplements — with or without calcium — protect against cancers. Yet little of the previous research included randomized trials, considered one of the strongest forms of studies. And none, according to the authors, have focused on only cancer. This new JAMA study did both, adding important evidence to the field.
For this trial, researchers randomly assigned 2,303 healthy US women to one of two groups: One group took either 2000 international units (IU) of vitamin D3 and 1500 milligrams of calcium daily; the second group was given identical placebos daily.
That amount is about three times the US government's recommendation of 600 IU's of vitamin D for adults through age 70, and 800 IU for those 71 and older. (This recommendation is for bone health.) Calcium recommendations for women over age 51 are 1200 mg with the upper limit for calcium supplements set at 2000 mg. High levels of calcium supplements can have health risks, such as greater chance of kidney stones.
After 4 years, there was no statistical difference in cancers diagnosed among the two groups of women. The researchers had examined the incidence of all cancers except non-melanoma skin cancers.
Negative effects that were potentially related to the supplements included kidney stones and elevated calcium levels.
The authors write that one explanation for not seeing any statistical difference between the treatment groups is that the women had higher vitamin D levels at the start of the study compared with the U.S. population. These women met the IOM recommendation for bone health at the start of the study.
An editorial in the same issue of JAMA points out that any potential cancer protection from vitamin D and/or calcium supplements may be limited to those who start out at low levels.
It may be that vitamin D only links to risk of specific cancers and this trial was not large enough. It’s also possible that the trial was not long enough. More research on the topic will help.
There are many possible reasons why individuals may want to take supplements but for cancer protection, AICR recommends not to rely on vitamin D or other supplements.
The study was funded by the National Institutes of Health.
Joan Lappe, Patrice Watson, Dianne Travers-Gustafson, Robert Recker, Cedric Garland, Edward Gorham, Keith Baggerly, Sharon L. McDonnell. Effect of Vitamin D and Calcium Supplementation on Cancer Incidence in Older Women. JAMA, 2017; 317 (12): 1234
Manson JE, Bassuk SS, Buring JE. Vitamin D, Calcium, and Cancer, Approaching Daylight?. JAMA. 2017;317(12):1217-1218. doi:10.1001/jama.2017.2155
Published on April 4, 2017