Published on October 24, 2018

There are many studies that have shown the connection between breast cancer and vitamin D, starting with the epiphany of the Garland Brothers when they first drove across the country in 1974, and then moving into many research studies, including our very own Breast Cancer Prevention Project.


What study found an 80% risk reduction for breast cancer?

This research paper, published in June 2018, combined the data from participants in two randomized controlled trials (RCT) and our Breast Cancer Prevention Project participants. The two RCTs were led by Dr. Joan Lappe, a member of our panel of scientists.

The first RCT, focused on bone health and cancer, was published in 2007 and is summarized in our blog here. This study followed 1,179 healthy, postmenopausal women, aged 55 or older for four years and put them in one of three groups – taking a daily dose of 1,100 IU vitamin D and 1,400-1,500 mg calcium; calcium only; or placebo only. The study found that the vitamin D and calcium group had a 77% reduced risk of cancer as compared to the placebo group.

The second RCT focused solely on cancer. The 2,303 women enrolled in this study received either 2,000 IU/day of vitamin D and 1,500 mg/day of calcium or placebo. This study found a 30% reduction in cancer incidence with the vitamin D + calcium group, as compared to the placebo group. (paper here, blog here)

The third set of women comes from the GrassrootsHealth Breast Cancer Prevention Project. This group of women self-select to be in the study. To match the entry requirements of the RCTs, data from women aged 55 or older with no current cancer and not in treatment for cancer were included. They are asked to conduct an at-home blood test every six months (they prick their finger and drop blood on a special card) and also answer a health questionnaire. At the time of this paper, there were 1,713 women enrolled whose data could be included in the analysis.

How is it different from other studies?

We summarize results from nine other breast cancer studies here. The big difference in this research is that the analysis assessed breast cancer risk across a broad range of 25(OH)D concentrations, including >40 ng/ml (most previous studies focused on the lower ranges).

Also, most vitamin D clinical trials are designed and interpreted by assigned treatment dose, not by blood levels of vitamin D. Not all people react the same to a specific dosage nor does this capture vitamin D from the sun, food and personal supplements. Therefore, it is better to report on blood levels achieved, than the dosage given. That way, all a person needs to do is monitor their blood levels, and use that as a measurement of sufficiency. (Recommended 40-60 ng/ml (100-150 nmol/L) or even now ≥ 60 ng/ml for cancer prevention)

How is it the same?

Many research studies show vitamin D reduces cancer risk, just like this one. If a trial shows no reduction in risk, it is worth looking at the details – Did the trial give enough vitamin D to produce a change? A relatively small dose, such as 400 IU/day, may not make a large enough change in vitamin D level for a difference in cancer risk to be observed. Did the trial follow participants long enough? Vitamin D changes take 2-3 months to change in the body and cancer may take longer to develop, so these trials should have longer time frames. And one common one, did they give vitamin D daily? It is explained here why that is important.

Treatment and control

Of the 5,038 women, 3,325 were enrolled in a study which assigned them to take a specific dose of vitamin D (1,100 IU or 2,000 IU /day) with calcium (1,400-1,500 mg/day), or two placebos. The remaining 1,713 women, enrolled in the Breast Cancer Prevention Project, were allowed to choose their supplement amount. They were also provided with information on the benefits of vitamin D and the importance of a blood level above 40 ng/ml (100 nmol/L) for good health. They were not in a “blind” study and received the results of periodic vitamin D tests. Many of them did achieve higher blood levels because they had a concrete goal, were measuring regularly, and were receiving feedback on whether or not their methods were effective.



As you can see, vitamin D levels have a significant correlation with breast cancer incidence. The horizontal, or x-axis, records increasing vitamin D levels, from 0 to 100 ng/ml. Note that the average vitamin D level for all women in the US is 29 ng/ml, for African Americans, 21 ng/ml. (Convert to nmol/L here.) The vertical, or y-axis, records the number of people in the study. The white dots represent breast cancer occurrence, note they are mostly below 40 ng/ml, and very rare above 60 ng/ml.

What is your next step?

Which side of this chart would you like to be on? Where would you like your wife? Your mother? Your children? Test today and start taking charge of your health.



Breast cancer risk markedly lower with serum 25-hydroxyvitamin D concentrations ≥60 vs <20 ng/ml (150 vs 50 nmol/L): Pooled analysis of two randomized trials and a prospective cohort
A GrassrootsHealth paper
Sharon L. McDonnell et al.
June 2018
Read Paper