While this method is more expensive than using animal cells, it is difficult to avoid the conclusion that the U.S. should follow suit. Although the Environmental Protection Agency had agreed with Great Lakes states to issue warnings about the fish in order to avoid damage to the developing brains of babies and children, Engler refused to issue the warnings in his state. Salmon are stocked in the waters as a boon to the Michigan recreation industry. Studies in the 1980s showed that women consuming Lake Michigan fish just two to three times per month were more likely to have children who were sluggish at birth, had a small head circumference, or showed cognitive difficulties. Higher levels of exercise reduced risk even further.
Exercise affects many aspects of physiology.
The reduction in cancer risk may relate to the fact that vigorous physical activity reduces the amount of estrogen the body produces. In extreme cases, it can even suppress ovulation. Women with less estrogen in their blood generally have less risk of breast cancer. Thune I, Brenn T, Lund E, Gaard M. Physical activity and the risk of breast cancer.