Vitamin D and breast cancer: sunlight or supplements?

By Stephen Daniells

- Last updated on GMT

Related tags: Breast cancer, Vitamin d

Higher vitamin D levels from exposure to sunlight, specifically
ultraviolet B (UVB), may reduce the incidence of breast cancer,
according to a new study.

Correlating data on cancer from 107 countries, scientists from the University of California, San Diego (UCSD) found that higher blood levels of vitamin D and living closer to the equator were associated with lower breast cancer incidence. "This is the first study, to our knowledge, to show that higher serum levels of vitamin D are associated with reduced incidence rates of breast cancer worldwide,"​ said Cedric Garland from UCSD School of Medicine. The study is published in the May-June 2008 issue of The Breast Journal​. However, commenting independently on the research, scientists from Yale University stated the results were confusing and shouldn't promote women to seek for more sun exposure. This suggests that increasing vitamin D levels should be achieved from fortified foods and dietary supplements. "While ultraviolet B radiation from the sun is the primary source of vitamin D in our body, unprotected sun exposure is not a recommended way to reduce a person's risk of developing breast cancer,"​ said David Leffell, M.D from Yale School of Medicine. A growing body of evidence has linked vitamin D to reduced incidences of cancer, but increasing vitamin D levels via sunlight or supplements has been a source of ongoing debate. In the US, where over 1.5 million people are diagnosed with skin cancer every year, experts are pushing supplements, claiming recommendations for sun exposure are "highly irresponsible". 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 refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. 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. There is growing evidence that 1,25(OH)2D has anticancer effects, but the discovery that non-kidney cells can also hydroxylate 25(OH)D had profound implications, implying that higher 25(OH)D levels could protect against cancer in the local sites. New data ​ Garland and co-workers used data from GLOBOCAN, a new tool developed by the World Health Organization's International Agency for Research on Cancer, to assess the incidence of breast cancer and vitamin D3 levels, triggered by exposure to UVB, in 107 countries. A dose-response was observed between blood vitamin D levels and the incidence of breast cancer, and vitamin D levels were correlated with sun exposure. "The findings of the present study are consistent with the four observational studies that reported an inverse association between oral intake of vitamin D and risk of breast cancer,"​ wrote the researchers. "Vitamin D and its metabolites may reduce the incidence of many types of cancer by inhibiting tumour angiogenesis, stimulating mutual adherence of cells, and enhancing communication through intercellular junctions, thereby strengthening contact inhibition of proliferation. The most active vitamin D metabolite, 1,25(OH)2D, has been shown to inhibit mitosis of breast epithelial cells. "Leadership from the public health community is needed to insure adequate oral intake of vitamin D3 and to encourage cautious exposure to sunlight in women whose skin type allows them to tan readily and not burn easily,"​ they concluded. Word of caution ​ Scientists from Yale were quick to state that the results may be confusing, and potentially dangerous, since cancer researchers have warned for decades the risk of skin cancer from unprotected sun exposure. "We are alarmed by the potential consequences of this study and urge women to continue to follow a careful sun protection program including the use of UV-blocking sunscreens. Women should absolutely avoid tanning salons,"​ said Leffell. Leffell suggested that the best way to reduce the risk of breast cancer was eat a healthy and balanced diet, exercise regularly, moderate alcohol consumption, and avoid weight gain. Evolutionary perspective ​ Previously, Boston University School of Medicine researchers wrote in the Journal of the American Academy of Dermatologists​ (doi:10.1016/j.jaad.2005.11.1057) that, from an evolutionary point-of-view, the trade-off between obtaining vitamin D from sunlight exposure and the effects of photoaging and skin cancer was sensible since lifespans were not very long. It does not make sense, the scientists argued, in a society where life expectancy has doubled and thirty per cent of Caucasians will develop skin cancer. Source: The Breast Journal​ May/June 2008, Volume 14, Issue 3, Pages 255-260 "Relationship between Low Ultraviolet B Irradiance and Higher Breast Cancer Risk in 107 Countries" ​Authors: S.B. Mohr, C.F. Garland, E.D. Gorham, W.B. Grant, F.C. Garland

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