(NaturalNews) Women with a higher vitamin D intake may be a quarter less likely to die from breast cancer than women with lower levels, scientists have found.
In a study published in the American Journal of Epidemiology, researchers from Mount Sinai Hospital in Toronto analyzed the vitamin D intake of 759 breast cancer patients and 1,135 women without breast cancer, accounting for both dietary intake and vitamin D production from exposure to sunlight. They found that women with a higher vitamin D intake had a 24 percent lower risk of acquiring hormone receptor-positive breast cancer than women with a lower vitamin intake.
"Few epidemiologic studies have considered the association between vitamin D and hormone-receptor-defined breast cancer," the researchers wrote.
Hormone receptor-positive breast tumors have their growth stimulated by the female sex hormones estrogen and progesterone, and are the most common form of breast cancer diagnosed in the United States.
The researchers also found that women with higher vitamin D intake had a 26 percent lower risk of developing hormone receptor-negative tumors, however, and a 21 percent lower chance of developing mixed-receptor tumors, which are receptive to only one hormone type. Unlike the correlation with receptor-positive tumors, these correlations were not statistically significant.
"This study suggests that vitamin D is associated with a reduced risk of breast cancer regardless of [hormone receptor] status of the tumor," the researchers wrote.
Breast cancer is the second most common and the fifth most lethal cancer in the world, with more than one million new diagnoses and 500,000 deaths each year. In the United States, 180,000 women are diagnosed with the disease and 40,000 are killed every year.
The current study is not the first to suggest that vitamin D intake may affect breast cancer risk and prognosis. In fact, the idea has been around since the 1940s, when researchers noted that cancer deaths increased with distance from the equator.
Technically a hormone, vitamin D is produced naturally by the body when the skin is exposed to sunlight. It has long been known to be critical for proper calcium absorption and bone health, and deficiency can lead to rickets in children and osteoporosis in adults.
Just 15 minutes of sun on the face and hands is considered to provide enough vitamin D for an average light-skinned individual, with 20 to 30 minutes needed for darker skinned people. Because the sun is weaker farther from the equator, however, many people are not able to synthesize all the vitamin D they need themselves, especially during winter months when the days are shorter. For people in those circumstances, dietary vitamin D is also available from certain fatty fish, in fortified grain and dairy products, and in the form of supplements.
Research has linked vitamin D deficiency to an increased risk of a wide variety of cancers, including cancers of the breast, colon, esophagus, pancreas and prostate. Another study conducted by University of Toronto and Mount Sinai Hospital researchers found that women who were vitamin D deficient at the time of breast cancer diagnosis had a 75 percent higher risk of death than women with adequate levels, and a 100 percent higher risk of having their cancer metastasize.
Recommended daily vitamin D intake remains controversial, with the governments of Canada and the United States recommending only 200 IU per day for children and 400 IU per day for adults, the amounts long accepted as necessary to stave off bone and dental problems. Recent research suggests that much higher levels are needed to protect against cancers, diabetes, heart disease and autoimmune disorders, however, leading the Canadian Cancer Society and other groups to recommend 1,000 IU per day for adults.