I'll never forget my mother's health advice to us as children: Drink your milk, eat your greens and get plenty of fresh air and sunshine.
When it comes to cancer prevention, it turns out mom was right.
Two new studies have uncovered exciting evidence of exceptionally strong cancer-protective effects of calcium and vitamin D from food or supplement sources.
The first study was published last week in the journal Archives of Internal Medicine by Dr. Jennifer Lin and colleagues from Harvard. They report that premenopausal women with high levels of vitamin D and calcium in their diets have a lower risk of breast cancer compared to women with lower intakes of these nutrients.
The second study, published in today's issue of the American Journal of Clinical Nutrition by Dr. Joan M Lappe and colleagues at Creighton University, goes even further: Dietary supplementation of these nutrients reduces the risk of multiple types of cancer.
Together, these studies provide robust evidence of the beneficial effects that calcium and vitamin D can have on cancer prevention.
Exploring Cancer's Nutrient Links
Research over the past half-century has pointed to a relationship between calcium, vitamin D and reduction of cancer risk, although the results have not been definitive.
In the 1950s, for example, scientists examined weather data and health statistics to show that areas of the country with the highest amount of sunshine, which stimulates the body to make vitamin D, had the lowest rates of colon cancer death.
Since that time, studies in both humans and animals have pointed toward cancer-preventive effects of both vitamin D and calcium, mainly for breast and colon cancers, but for other cancers as well, ranging from prostate cancer to non-Hodgkin's lymphoma.
Lin and her Harvard colleagues focused on these nutrients' effects on breast cancer by analyzing data from the Women's Health Study, funded by the National Institutes of Health.
This study followed 10,578 premenopausal and 20,909 post-menopausal women 45 years or older who were initially free of cancer over 10 years, collecting data on diet, over-the-counter supplement use and subsequent development of breast cancer.
Amazingly, what they found was that calcium and vitamin D intake reduced the risk of developing breast cancer, but only among premenopausal women.
For these women, those with the highest intake of calcium were 39 percent less likely to develop breast cancer than those with the lowest intake. Those in the group with the highest intake of vitamin D were also 35 percent less likely to develop breast cancer.
What's more, high intakes of calcium and vitamin D among premenopausal women seemed to reduce the most aggressive breast tumors, including larger tumors, those which spread to the lymph nodes and those with the most dangerous types of cancer cells.
Unfortunately, among post-menopausal women, there was no relationship between calcium and vitamin D intake and prevention of breast cancer. Nonetheless, when the two nutrients were taken together in high amounts, there was a suggestion of benefit.
Beyond Breast Cancer
In a second study, Lappe and colleagues followed nearly 1,200 women from a nine-county area in eastern Nebraska to see whether vitamin D and calcium supplements might reduce not just breast cancer, but all cancers.
Compared to those women taking a placebo, cancer risk of any kind over 10 years decreased by 60 percent in those taking both calcium and vitamin D, and by 47 percent in those taking calcium alone.
Moreover, when they excluded those cancers that occurred in the first year of the study — based on the assumption that these cancers were likely present at the start of the study — the benefit of calcium plus vitamin D appeared even more dramatic: a 77 percent decrease in cancer risk.
These are stunning results. Even if the authors could not definitively say calcium reduced cancer risk, a number of other studies bore out calcium's protective effect. The authors can say with a strong degree of confidence that combining calcium with vitamin D is highly beneficial.
How It Works
Experimentally, calcium and vitamin D have been shown to exert their anti-cancer effect by interfering with the action of a hormone called insulinlike growth factor, or IGF.
The IGF hormone stimulates breast cancer cells — as well as cells of other types of cancer — to divide. Calcium and vitamin D interact with IGF to disrupt such cell growth; in fact, vitamin D can effectively block IGF's effect.
Other factors might also come into play. In laboratory animals, for example, diets low in vitamin D and calcium increased the number of breast tumors. Amazingly, diets rich in these nutrients caused the disappearance of many worrisome breast cells, the types of cells that can eventually become cancerous.
While the Harvard study evaluated self-reports of usual food intake from dietary questionnaires, the Nebraska study actively gave patients calcium and vitamin D pills. This has important implications: Cancer risk can be reduced both by calcium and vitamin D in the diet, as well as by using over-the-counter supplements of these nutrients.
One should note, however, that both studies were carried out exclusively among women, and thus might not fully apply to men. However, given previous studies suggesting a reduction in male cancers (e.g., prostate cancer) by calcium and vitamin D, it is likely that this effect is not bound by gender.
Moreover, some of the cancers prevented among the women in the Nebraska study included cancers that also affect men, such as colon and lung cancers and leukemia.
Protect Yourself With Diet
Calcium is largely derived from the diet and is found in dairy products, leafy green vegetables, fortified juices and nuts. Many people, particularly women, also take calcium supplements to strengthen their bones.
Vitamin D is found in oily fish (salmon, sardines), as well as fortified foods such as milk and some cereals. Another major source of vitamin D for most people is exposure to sunshine.
Although the recommended daily allowance of vitamin D is 400 IU, some authorities suggest that up to 1000 I,U might be necessary to achieve optimal blood levels, especially when sun exposure is rare (e.g., during the winter or among home-bound individuals).
Of course there are other important benefits of adequate vitamin D and calcium intake: the prevention of osteoporosis, a thinning of the bones that increases bone fragility making bones more likely to break.
So follow mom's advice: Drink your milk, finish your spinach and get plenty of fresh air and sunshine. And dietary supplements of calcium and vitamin D are also important. If you are a woman who has not gone through menopause, you likely will decrease your risk of breast cancer.
And no matter what your age, you will improve the health of your bones, and probably your overall cancer risk as well.
Dr. John Spangler is a professor of family medicine at Wake Forest University School of Medicine.