A new Japanese study has reported that relatively high vitamin D and calcium intakes are both associated with modestly reduced risk of breast cancer. Findings of previous studies that investigated the possible associations have been inconsistent. The study included 1,803 breast cancer cases and 3,606 cancer-free controls who were matched by age and menopausal status. However, when the analysis was performed according to the menopausal status of the study participants, the reduced risk conferred by vitamin D was found only among premenopausal women and the reduced risk association with calcium intake was found only among postmenopausal women.

Study results might not apply to U.S. women

While the study results are similar to some U.S. and European findings, they should be viewed with caution since the Japanese diet is very dissimilar to the typical Western diet. For example, U.S. women typically derive much more of their calcium from dairy products and less of it from vegetables than Japanese women. In addition, Japanese women normally derive more vitamin D from their diets due to their high fish consumption, whereas U.S. women are often deficient in vitamin D.

Increasing Vitamin D also associated with lower risk in Western populations

Vitamin D appears to be an integral part of breast cancer development and progression, but the relationship is not fully understood. Below, we summarize recent findings with respect to vitamin D and risk of breast cancer in Western populations:

  • A 2009 meta-analysis of 36 studies concluded that there was a significant inverse relationship between vitamin D intake and risk of breast cancer. Also found was a significant decrease in risk of breast cancer for those with the highest calcium consumption
  • A large Swedish prospective study found no significant relationship between risk of breast cancer and sun exposure variables, including annual number of sunburns, skin sun sensitivity, time spent on sunbathing vacations, or solarium use at any age of exposure. There was also no association found between breast cancer incidence and dietary vitamin D intake or supplementary multivitamin use
  • A Canadian case-control study found that while vitamin D intake was most strongly associated with lower risk of hormone receptor positive (ER+/PR+) breast cancer, it also appeared to be associated with lower risks of hormone receptor negative (ER-/PR-) and mixed receptor status (ER+/PR-) tumors
  • An Italian study found that risk of breast cancer was significantly lower for women in the top three tenths of vitamin D intake than those in the bottom three tenths. In fact, no protection was found for vitamin D up to the seventh decile of intake. The inverse association between high intake of vitamin D and breast cancer was consistent regardless of menopausal status
  • A study of women with at least one first-degree or second-degree relative with breast or ovarian cancer found that breast density was inversely associated with vitamin D intake. High breast density has been found to be associated with increased risk of breast cancer
  • A Canadian case-control study found that increasing sun exposure during ages 10 to 19 was associated with lower subsequent risk of breast cancer. Reduced risk was also found for cod liver oil consumption and increasing milk intake. Weaker evidence was found for associations between ages 20 and 29 and none between ages 45 and 54. The authors concluded that vitamin D exposure earlier in life, particularly during breast development, may be most relevant.

Relationship between calcium intake and risk of breast cancer is less clear

While several studies have reported an inverse association between calcium intake and risk of breast cancer, the association is less clear than that of vitamin D. Calcium has been shown to have anti-proliferative effects on breast cancer cells in the laboratory and to inhibit the development of mammary tumors in mice. However, levels of calcium in the blood of breast cancer patients may be elevated because of effects of breast tumors on calcium homeostasis. Some women at high risk for breast cancer have subclinical hyperparathyroidism, which elevates calcium levels. One study found that relatively high levels of calcium in benign breast tissue may be associated with a modest increase in risk of breast cancer. Nevertheless, dietary intake of calcium, especially in childhood and young adulthood, appears to be protective against breast cancer:

  • A Swedish prospective study found that while dietary calcium intake was not associated with breast cancer risk overall, relatively high calcium intake was associated with a lower risk of hormone receptor negative breast cancer ER-/PR-
  • A French prospective study found that calcium intake was associated with lower risk of breast cancer, especially among premenopausal women
  • A U.S. prospective study found that higher intakes of total calcium and vitamin D were both moderately associated with a lower risk of premenopausal breast cancer
  • Another U.S. prospective study of postmenopausal women found that women with the highest intake of dietary calcium (greater than 1,250 mg per day) were at a lower risk of breast cancer than those reporting up to 500 mg per day. The association was slightly stronger among women with estrogen receptor positive (ER+/PR+) tumors. However, use of supplemental calcium was not found to be associated with risk of breast cancer.

Since milk and butter have been found to be associated with higher risk of breast cancer in adult women, we suggest obtaining calcium from other sources, including the following:

Brussels sprouts
Cheese, low-fat
Collard greens
Green beans
Mustard greens
Yogurt, low-fat

Please see our article on how to optimize your breast cancer diet for information on what to eat during all stages of treatment and recovery.