Breast Cancer and Vitamin D

sunbathingVitamin D is produced in the skin on exposure to sunlight. Known as the sunshine vitamin, it reduces risk of breast and colon cancer when our levels are adequate. Time spent outdoors is associated with reduced breast cancer risk during all phases of a woman’s life. How much sun exposure is needed? Only 5-10 minutes of exposure of the arms and legs or the hands, arms, and face, 2 or 3 times per week.

Vitamin D deficiency is common in at least 60% of women. Raising the minimum year-around serum 25(OH)D level to 40 to 60 ng/mL (100-150 nmol/L) would prevent approximately 58,000 new cases of breast cancer and 49,000 new cases of colorectal cancer each year, and three fourths of deaths from these diseases in the United States and Canada. A combined solar vitamin D score, including all the variables related to vitamin D production, is significantly associated with reduced breast cancer risk. 2000 IU per day of vitamin D(3) taken daily is safe, and often more is needed to achieve ideal blood levels. Joint pain in postmenopausal women taking aromatase inhibitors is significantly decreased when women take 50,000 IU of vitamin D per week, with no harmful side effects. 25OHD levels ideally should be above 66 ng/ml (150 nmol/L) to achieve this result.

Most of us depend on sun exposure to satisfy our requirements for vitamin D. Solar ultraviolet B photons are absorbed by 7-dehydrocholesterol in the skin, leading to its transformation to previtamin D3, which is rapidly converted to vitamin D3. Season, latitude, time of day, skin pigmentation, aging, sunscreen use, and glass all influence the skin production of vitamin D3. Once formed, vitamin D3 is metabolized in the liver to 25-hydroxyvitamin D3 and then in the kidney to its biologically active form, 1,25-dihydroxyvitamin D3. Vitamin D deficiency is an unrecognized epidemic among both children and adults in the United States. Vitamin D deficiency not only causes rickets among children but also precipitates and exacerbates osteoporosis among adults and causes the painful bone disease osteomalacia. Vitamin D deficiency has been associated with increased risks of deadly cancers, cardiovascular disease, multiple sclerosis, rheumatoid arthritis, and type 1 diabetes mellitus. Maintaining blood concentrations of 25-hydroxyvitamin D above 80 nmol/L (approximately 30 ng/mL) not only is important for maximizing intestinal calcium absorption but also may be important for providing the extrarenal 1alpha-hydroxylase that is present in most tissues to produce 1,25-dihydroxyvitamin D3. Although chronic excessive exposure to sunlight increases the risk of nonmelanoma skin cancer, the avoidance of all direct sun exposure increases the risk of vitamin D deficiency, which can have serious consequences. Monitoring serum 25-hydroxyvitamin D concentrations yearly should help reveal vitamin D deficiencies. Sensible sun exposure (usually 5-10 min of exposure of the arms and legs or the hands, arms, and face, 2 or 3 times per week) and increased dietary and supplemental vitamin D intakes are reasonable approaches to guarantee vitamin D sufficiency.

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