Questions and Answers About Calcium
What is calcium?
Calcium is a mineral that is needed for basic blood vessel, muscle, and nerve functions, cell-to-cell signaling, and hormone release. It is the most common mineral in the body. The body stores calcium mainly in bone tissue. Calcium naturally occurs in some foods and is added to other foods. It is also available as a dietary supplement.
How is calcium administered or consumed?
The main sources of calcium in the American diet are foods and dietary supplements. About one-third of dietary calcium comes from milk and milk products like cheese and yogurt. Vegetable sources include Chinese cabbage, kale, and broccoli. Spinach contains calcium but it is not in a form that is well absorbed by the body. Foods with calcium added include many fruit juices and drinks, tofu, and cereals.
In the United States, almost half the population takes dietary supplements containing calcium. However, most research about calcium and prostate cancer risk has studied only calcium consumed in the diet and not calcium taken in supplements.
Have any preclinical (laboratory or animal) studies
been conducted using calcium?
Studies of calcium in the laboratory have shown the following:
- In a 2011 study, prostate cancer cells were treated with cow milk, almond milk, soy milk, casein, or lactose. Growth of prostate cancer cells (LNCaP) was stimulated when they were treated with cow milk. Treatment with soy milk did not affect the growth of prostate cancer cells, and treatment with almond milk treatment slowed the growth of prostate cancer cells.
Studies of calcium in animal models of prostate cancer have shown the following:
- Strains of mice which developed prostate cancer that acts like human cancer were fed low-calcium diets or high-calcium diets. Prostate cancer growth was found to be similar in mice fed either low- or high-calcium diets.
- Dietary vitamin D and calcium were studied in mice injected with prostate cancer cells and fed specific diets (including high-calcium plus vitamin D or normal calcium and no vitamin D). The mice that received the normal calcium and no vitamin D diet had more prostate cancer growth than mice fed the other diets.
Have any clinical trials (research studies with people)
of calcium been conducted?
Studies of people in many parts of the world have been done to find out if there is a link between dairy products, calcium, and prostate cancer risk.
Population studies of dairy products, dietary calcium, and prostate cancer risk have shown mixed results. These studies may be hard to interpret because other major nutrients in dairy products, such as fats, and factors such as age and body mass index have not been taken into account.
Overall, however, studies suggest that high total calcium intake may be linked with increased risk of advanced and metastatic prostate cancer compared with lower amounts of calcium. More studies are needed about the effects of calcium and/or dairy products on prostate cancer risk and how these effects develop in the body.
Clinical trial of preventing prostate cancer
In a randomized clinical trial reported in 2005, men were given calcium (1200 mg/day) or a placebo for 4 years and were followed up for 12 years. During the first 6 years of the study, there were markedly fewer cases of prostate cancer in the calcium group compared to the placebo group. After 10 years, however, there was no meaningful difference in the number of prostate cancers in the calcium group compared to the placebo group.
Reviews of many studies combined
Reviews of many studies combined showed mixed findings about whether consuming calcium and dairy products affects the risk of prostate cancer:
- A 2005 review of many studies found a possible link between an increased risk of prostate cancer and a diet high in dairy products and calcium. See the PDQ summary on Prostate Cancer Prevention for more information.
- A 2008 review of 45 observational studies found no link between consuming dairy products and the risk of prostate cancer.
- A review of cohort studies published between 1996 and 2006 found that consuming milk and dairy products did increase the risk of prostate cancer.
- A 2013 review for the U.S. Preventive Services Task Force found that taking Vitamin D and/or calcium supplements showed no overall effect on rates of cancer or deaths from cancer, including prostate cancer.
Is calcium approved by the U.S. Food and Drug Administration (FDA)
for use as a cancer treatment in the United States?
Calcium is available in the United States in food products and dietary supplements. Because dietary supplements are regulated as foods, not as drugs, FDA approval is not required unless specific claims about disease prevention or treatment are made.
Current Clinical Trials
General information about clinical trials is also available from the NCI Web site.