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Health News Archive 594 - Breast Cancer
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Long-Term Vitamin D Intake Linked to 30% Lower Breast Cancer Risk

Increased vitamin D levels during youth, from the sun and diet, may reduce the risk of breast cancer later in life by over 30 percent, suggests a new epidemiological study. The study, by researchers at Mount Sinai Hospital in Canada, adds to a rapidly growing body of science reporting potential benefits of vitamin D against cancer that has led for calls to increase recommended intake levels.

The link between vitamin D intake and protection from cancer dates from the 1940s when Frank Apperly demonstrated a link between latitude and deaths from cancer, and suggested that sunlight gave "a relative cancer immunity." Vitamin D levels have also been linked to skin color - darker skinned people produce less vitamin D on exposure to the sun, relative to fair-skinned people.

Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive. The latter is derived from plants and only enters the body via the diet. Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.

According to Julia Knight, lead author of the study, there was only limited evidence in humans that vitamin D-related factors may reduce breast cancer risk. The researchers recruited 972 women with newly diagnose invasive breast cancer and 1,135 randomly selected healthy controls and interviewed to assess vitamin D-related variables, such as sunlight exposure (outdoor activity), cod liver oil and supplement intake and milk consumption.

After adjusting for potential confounding factors, scientists found that increased exposure to sunlight during adolescence was associated with the highest protection against breast cancer risk later in life, with a 35 percent risk reduction. Significant risk reductions were also observed for increased cod liver oil intake (24 percent risk reduction), and drinking at least 10 glasses of milk per week was associated with a 38 percent risk reduction. Similar exposures later in life (ages 20 to 29) were associated with smaller risk reductions, while no protective effects from any vitamin D sources were observed for ages 45 to 54.

"We found strong evidence to support the hypothesis that vitamin D could help prevent breast cancer. However, our results suggest that exposure earlier in life, particularly during breast development, may be most relevant," concluded the researchers in the journal Cancer Epidemiology Biomarkers & Prevention. The study does have several important limitations, notably being based on recall of dietary habits early in life as well as outdoor exposure, both of which are susceptible to recall errors from the participants.

Calls to increase vitamin D intake have been growing. Indeed, only recently fifteen experts from universities, research institutes, and university hospitals around the world called for international agencies to "reassess as a matter of high priority" dietary recommendations for vitamin D because current advice is outdated and puts the public at risk of deficiency (The American Journal of Clinical Nutrition, Vol. 85, pp. 860-868).

Source: J.A. Knight, M. Lesosky, H. Barnett, J.M. Raboud, R. Viethe Vitamin D and Reduced Risk of Breast Cancer: A Population-Based Case-Control Study; Cancer Epidemiology Biomarkers & Prevention
March 2007, Volume 16, Pages 422-429. doi: 10.1158/1055-9965.EPI-06-0865

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