Risk Factors For Breast Cancer - Obesity and Lack of Exercise

Obesity and Lack of Exercise

Gaining weight after menopause can increase a woman's risk. A 2006 study found that putting on 9.9 kg (22 lbs) after menopause increased the risk of developing breast cancer by 18%. Lack of exercise has been linked to breast cancer by the American Institute for Cancer Research.

Obesity has been linked to an increased risk of developing breast cancer by many scientific studies. There is evidence to suggest that excess body fat at the time of breast cancer diagnosis is associated with higher rates of cancer recurrence and death. Furthermore, studies have shown that obese women are more likely to have large tumors, greater lymph node involvement, and poorer breast cancer prognosis with 30% higher risk of mortality.

Weight gain after diagnosis has also been linked to higher rates of breast cancer recurrence or mortality although this finding is not consistent. Weight gain is often less severe with newer chemotherapy treatments but one study found a significant risk of breast cancer mortality in women who gained weight compared to those who maintained their weight. However, other cohort studies and recent clinical trials have not shown a significant relationship between weight gain after diagnosis and breast cancer mortality.

Weight loss after diagnosis has not been shown to decrease the risk of breast cancer recurrence or mortality. However, physical activity after breast cancer diagnosis has shown some associations with reducing breast cancer recurrence and mortality independent of weight loss. Data for both weight loss and physical activity and the effect on breast cancer prognosis is still lacking.

There is debate as to whether the higher rate of breast cancer associated with obesity is due to a biological difference in the cancer itself, or differences in other factors such as health screen practices. It has been suggested that obesity may be a determinant for breast cancer screening by mammography. Seventeen scientific studies in the United States have found that as obesity increases in women over 40 years of age the rate of mammography reported decreases significantly. When stratified by race (white vs. black) there was a stronger relationship between obesity and lack of mammography screening among white women. Another study also found lower rates of mammography among those who were overweight and obese compared to those women who were of normal body mass index—this effect was only seen in white women. Obese women are more likely to list pain associated with mammograms as a reason for not getting screened; however, leaner women also list this as a reason for avoiding mammograms. Other reasons obese women may avoid mammography are due to lack of insurance, low income, or embarrassment at the procedure, although when these factors are accounted for, the effect of lower rates of screening are still significant. In contrast, other studies have shown that mammography patterns did not differ among women who were obese compared to those at a healthy weight indicating that there may be biological differences in cancer presentation between these groups.