The investigation, known as the MARIE study, focused on the previously unexamined questions of how much exercise women should engage in to get an anti-breast-cancer benefit, and in which period in their lives, and which types of breast cancer are most prevented by physical activity.
The research team, led by Professor Jenny Chang-Claude and conducted at the German Cancer Research Center and the University Hospitals of Hamburg-Eppendorf, selected 3,464 breast cancer patients and 6,657 healthy women from the ages of 50 to 74. They were questioned about their physical activity habits during two of their life periods – from 30 to 49 years of age and from 50 until the present.
When the healthy and breast cancer groups were compared, after adjusting for various cancer-risk factors, the scientists found that the physically most active participants had an approximately one-third lower risk of developing breast cancer than inactive women. But even those women who were physically active for only 30 minutes a day received significant protective benefit from breast cancer.
In addition, women who exercised after turning 50 received the greatest protective benefit. Regarding the different levels of protection from various types of breast cancer that exercise bestows, the study found that active women have less risk of affliction by tumors that form receptors for estrogen and progesterone, the two female sex hormones. These malignancies accounted for 62.5 percent of breast cancers among MARIE subjects. Other breast tumors were not affected by physical activity.
The effect of physical activity was unrelated to body weight and calorie intake. From this, the researchers concluded that physical activity cuts cancer risk through hormonal mechanisms, not just by a reduction of body fat or other changes in physical constitution, as has been assumed.