April 2017 Health Bulletin

Does vitamin D and calcium lower cancer risk in older women?

It has been thought that low vitamin D levels are linked to an increased risk of some cancers such as colon cancer. Consequently a large study was designed to look at the protective effect of vitamin D and calcium supplementation in healthy postmenopausal women on the risk of all types of cancer.

Vitamin D consists of two biologically equivalent forms:

  • Vitamin D2: from vegetable sources in the diet or supplements
  • Vitamin D3: made from cholesterol through sun exposure, animal diet sources and supplements

A person’s blood level of total 25-hydroxyvitamin D (25-OH-VitD) (the sum of 25-OH-vitamin D2 and 25-OH-vitamin D3) reflects their vitamin D body stores.

Healthy postmenopausal women, aged 55 years and older from Nebraska, USA, participated in this randomized controlled trial. Two thousand, three hundred and three study participants were given either Vitamin D3 (2000 IU) and calcium (500mg) daily, or an identical placebo to take for 4 years.

The primary outcome was the occurrence of any type of cancer (excluding non-melanoma skin cancers). Secondary outcomes were specific cancer diagnoses, including breast, lung, colon, lymphoma, leukaemia and myeloma. Secondary outcomes also included blood pressure, heart disease, osteoarthritis, bowel polyps, diabetes, upper respiratory infections and falls.

The average blood Vitamin D level at the beginning of the study was 32.8 ng/ml (81.9 nmol/l Australian units) which is not considered vitamin D deficient. After one year the average level was 43.9 ng/ml (109.6 nmol/l) in the treatment group and 31.6 ng/ml (78.9 nmol/l) in the placebo group. All levels 25(OH)D after baseline were significantly greater in the treatment group than in the placebo group.

Calcium supplementation was used in this trial as a previous study had shown a combination of Vitamin D and calcium reduced the incidence of cancer where the calcium only group showed no significant effect on cancer incidence. In humans a high calcium intake has been associated with a lower risk of colon cancer and adenomas.

Over the four years of the trial the incidence of any new cancer was 3.89% in the group taking study supplementation and 5.58% in the placebo group which was statistically not a significant difference. The incidence of breast cancer was also similar for the groups.

High blood calcium or kidney stones did not occur more frequently than would be expected in older women.

Strengths of this study were the population based random controlled design, with a relatively low dropout rate; testing of baseline and annual 25(OH)D levels, 6 monthly reviews at the research unit; and validated cancer outcomes with pathology reports.

The limitations were that the population in general were not Vitamin D deficient to begin with, the participants were older women, and primarily non-Hispanic white. Participants in the placebo group were allowed to take their own vitamin D and calcium though were asked not to exceed the National Academy of Medicine recommended intake level of vitamin D 800IU per day and calcium 1500mg per day. The sample size calculations were based on a study where participants had a lower baseline 25(OH)D level which may have limited the power to find the effect of vitamin D3 supplementation. The analysis excluded cancers diagnosed in the first year of the study as the premise used was that these were probably present prior to commencement of the study.

The researchers concluded that supplementation with vitamin D3 and calcium in healthy postmenopausal women (whose baseline 25-OH Vit D level was 89.9 nmol/l) did not significantly lower the risk of all types of cancer over a 4 year period when compared with placebo.

Effect of Vitamin D and Calcium Supplementation on Cancer Incidence in Older Women: A Randomized Clinical Trial, Lappe J, Watson P, Travers-Gustafson D, Recker R, Garland C, Gorham E, Baggerly K, McDonnell SL. Jama 2017 Mar 28;317(12): 1234-1243.

Information provided might not be relevant to a particular person's circumstances and should always be discussed with that person's own healthcare provider.