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The British Medical Journal reports that a new review confirms the beneficial effect of physical activity on breast cancer risk and further finds that women who exercised the most had a 25% less breast cancer risk than women who exercised the least.
A lifetime of physical activity (compared with only several years or months) and vigorous physical activity (compared with mild or moderate) were associated with even greater cancer protection. The majority of studies suggest that the more a person exercises, the more benefits she might gain.
The association between physical activity and decreased cancer risk was strongest in postmenopausal women, women with a normal body mass index, and non-white racial groups.
One recent study found that women who exercised throughout their lifetime had a 23% lower risk of premenopausal breast cancer than women with less activity. The women’s activity levels were equivalent to 3.25 hours per week of running or 13 hours per week of walking. High activity levels from 12 to 22 years old were associated with the lowest risk in that study.
Physical activity may reduce cancer risk by lowering the levels of hormones such as estrogen, insulin, and insulin-like growth factor. These hormones are important for health but when present in excess can promote cancer development in certain people.
An Institute of Medicine report recommends that women exercise moderately for 60 minutes each day. This may include brisk walking (faster than three miles per hour) or running. Children should engage in 90 minutes or more of physical activity each day. Tips for a successful exercise plan include:
(Br J Sports Med 2008; doi:10.1136/bjsm.2006.028132; J Natl Cancer Inst 2008;100:728–37)