For years, researchers have suspected that low levels of vitamin D in the body might raise the odds a woman will develop breast cancer, but hard scientific proof has been lacking. Now a new study conducted by scientists at the German Cancer Research Center (Deutsches Krebsforschungszentrum, DKFZ), collaborating with researchers of the University Hospitals in Hamburg-Eppendorf, provides evidence that women with low blood levels of vitamin D clearly have a substantially increased risk of breast cancer.
The study, published in the medical journal Carcinogenesis, involved 1,394 breast cancer patients and an equal number of healthy women. All were post-menopausal. While earlier studies have looked primarily at how much vitamin D was in women’s diets, the German scientists documented the women’s total vitamin D status, measuring both vitamin D intake from food and also the vitamin D created by the body when exposed to sunlight. To this end, the scientists took measurements of serum 25-hydroxy vitamin D [25(OH)D], a vitamin D metabolite that indicates overall vitamin D status.
The results? Women with a very low blood level of 25(OH)D had a considerably increased breast cancer risk.
The anti-cancer properties of vitamin D might be explained by the fact the vitamin influences cell growth, cell differentiation and programmed cell death (apoptosis). The research team, headed by Dr. Jenny Chang, also pointed out that vitamin D may exert its cancer-preventing effect by counteracting the growth-spurring effect of estrogens. “Our findings strongly suggest a protective effect for post-menopausal breast cancer through a better vitamin D supply,” the scientists concluded.
In addition to its impact on cells, vitamin D regulates calcium metabolism in the human body. Besides upping cancer risk, a lack of vitamin D can contribute to fatigue, recurring infections, poor stamina and some forms of asthma. Foods that are high in vitamin D include sea fish (cod liver oil), eggs and dairy products.
However, as the German researchers emphasized in their paper, the largest portion of vitamin D is produced by our own body with the aid of sunlight. Unfortunately, Americans often do not have enough exposure to sunlight for optimum health, according to physician Dr. James E. Dowd, author of the new book “The Vitamin Cure” (Wiley). Dr. Dowd says 55 percent of children and 60 percent of all people in the United States lack healthful levels of vitamin D.
An earlier study published in Cancer Epidemiology Biomarkers Prevention found that daily consumption of dairy products reduce the risk for postmenopausal breast cancer. The authors suggested that calcium and vitamin D in dairy foods may lower the risk for cancer due to both direct effects on cell proliferation and hormones.
According to the National Cancer institute, 182,360 new cases of breast cancer in women are expected to be diagnosed in 2008.