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Sun exposure reported to reduce the risk of breast cancer

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We are fortunate to enjoy sunny days outdoors on days when a good part of the US is enduring arctic condition. Sun exposure us allows our bodies to manufacture Vitamin D; however, it also exposes us to the risk of sun damage to our skin, including skin cancer. A new study has reported that sun exposure might reduce the risk of another malignancy—breast cancer. The study was published in the February edition of the journal Environmental Health Perspectives by researchers at the University of North Carolina and the National Institutes of Health.

The authors note that some epidemiologic studies have reported a decreased risk of several types of cancer, including breast cancer, from sunlight exposure. They theorized that the risk reduction might be due to sunlight promoting the production of Vitamin D by the skin. They note that dermal (skin) synthesis is the primary source of Vitamin D for most individuals, and that diet and supplements are usually minor contributors. Therefore, they conducted a study to evaluate sun exposure and its interaction with Vitamin D receptor (VDR) gene variants on breast cancer risk.

The study group comprised 31,021 private pesticide applicators’ wives, including 578 women enrolled in the prospective (forward-looking) Agricultural Health Study cohort; the women were followed for an average of 8.6 years. The investigators estimated interactions between sun exposure, VDR variants, and breast cancer in 293 women with sun exposure and 586 matched controls. Information on sun exposure was obtained by a questionnaire when the women enrolled in the study. The data was subjected to statistical analysis to determine relative risks.

Over the 10-year follow-up period, the researchers noted a small decrease in breast cancer risk among women with usual sun exposure of one or more hours a day, compared to those who reported less than one hour of exposure per day. The association appeared to be slightly greater in relation to estrogen receptor–positive tumors than estrogen receptor–negative tumors. The risk reduction for sunlight exposure of one or more hours a day and one VDR variant gene was not significant.

The authors concluded that their results suggested that sun exposure may be associated with reduced risk of breast cancer; however, they did not find clear evidence of modification of that risk by VDR variants. They recommended that further, larger studies should be conducted, particularly among groups of women in which low levels of usual sun exposure can be more accurately measured.

Take home message:
It is likely that the lowered breast cancer risk was due to higher Vitamin D levels resulting from sun exposure. Many individuals are deficient in Vitamin D, and Vitamin D supplements are inexpensive. This can be detrimental to one’s health because the vitamin has many health benefits, including promoting bone health and fighting infections. The current recommended dietary allowance (RDA) is 600 international units (IU) for everyone aged 1-70, and 800 IU for adults older than 70.

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