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Associations have been made between breast cancer risk and a woman’s body mass, diet, level of activity, and the amount of alcohol consumed. As with exposures to many environmental factors that influence breast cancer risk, the effects of these lifestyle factors vary over the course of a woman’s lifetime depending on her exposure to estrogen and estrogen-like substances.

Obesity after menopause

Obesity after menopause is considered a risk factor for breast cancer in part because higher body fat levels are associated with increased production of estrogens from sources other than the ovaries. (The ovaries stop being a major source of estradiol after menopause.) Postmenopausal women who are obese have estradiol levels that are up to twice as high as non-obese women within the same age group [Key et al., 2003].

Recent data suggest that the increased risk posed by obesity is most pronounced in women who have gone through menopause in the past few years (as compared with older postmenopausal women) and in women who have never used hormone replacement therapy [Morimoto et al., 2002].

In postmenopausal women who have already been treated for breast cancer, obesity is associated with an increase in blood levels of estradiol and testosterone, and in both premenopausal and postmenopausal breast cancer patients, obesity is associated with an increased rate of cancer recurrence and mortality [McTiernan et al., 2003; Loi et al., 2005].

Dietary factors

Many studies indicate that postmenopausal women who consume diets that are low in fiber and high in fat, especially saturated fats, have increased risks for breast cancer [Richter, 2003]. Fat stores toxins and increases the amount of estrogen in the blood. Some studies suggest that women who consume high-fat Western diets have more estrogen in their blood and less urinary excretion of estrogen as compared with women who eat higher-fiber, low-fat diets [Goldin et al. 1982].

Recent data suggest a more complicated story, with many studies showing no single dietary factor being associated with a general increased risk of breast cancer. Rather, dietary components may be important in association with other factors such as smoking or age [Fung et al., 2005]. In particular, dietary patterns in adolescence may affect later risk for developing breast cancer [Frazier et al., 2003].

Dietary risks may be culturally defined: different populations with their own traditional diets may be sensitive to excesses or imbalances in different dietary components. For example, a recent study examining dietary factors and breast cancer risk among Mexican women revealed a significant association with increased breast cancer risk of high carbohydrate intake, but not high fat intake [Romieu et al. 2004].

Alcohol consumption

The risk of breast cancer increases as alcohol consumption increases, with two or more daily drinks being associated with increased breast cancer risk [Longnecker et al. 1995; Smith-Warner et al., 2003]. Moderate drinking leads to significant increases in circulating estradiol levels. In addition, alcohol is metabolized to acetaldehyde, a chemical that is directly carcinogenic, causing harmful effects on DNA synthesis and repair [Poschl and Seitz, 2004]. Interestingly, at least one recent study suggests that a particular genetic profile may predispose a woman to sensitivity to alcohol with regards to increased breast cancer risk [Coutelle et al., 2004].


Studies examining the effects of smoking on breast cancer risk have yielded controversial and sometimes contrary results, with some studies suggesting that smoking may be anti-estrogenic and therefore decrease the risk for breast cancer and others suggesting that direct carcinogenic effects of tobacco smoking may increase risks for the disease One recent study explored age of onset of smoking, amount smoked, reproductive history and age at breast cancer onset [Band et al., 2002].

Results indicated that smoking increased the risk of breast cancer, but only in pre-menopausal women who began smoking in the first few years following onset of menstruation, or in pre-menopausal women who had never given birth regardless of age of onset of the use of cigarettes. Both early-pubertal breasts and nulliparous breasts are particularly sensitive to the effects of carcinogens [Russo and Russo, 1998].

In addition to examining the direct effects of smoking on cancer risks, scientists are increasingly interested in the effects of ‘second hand’ smoke. For example, one study has shown that women who have lived with a spouse who smoked for over 25 years have a two-fold increase in breast cancer rates as compared to otherwise similar women whose spouses do not smoke [Gammon et al., 2004].

Exercise level

The great majority of studies examining a possible relationship between breast cancer risk and physical activity have found that physical activity is associated with a decreased risk of developing breast cancer in postmenopausal women [Friedenreich & Orenstein, 2002]. Across the multiple studies, evidence for this protective relationship is strongest for postmenopausal women [Friedenreich, 2004]. Data are less consistent for whether or not physical activity affords a relative protection against breast cancer for premenopausal women.

The effectiveness of physical activity in decreasing breast cancer risk is most pronounced in postmenopausal women with the highest level of activity [John et al., 2003; Patel et al, 2003]. Recent studies have reported possible interactions of physical activity and other factors in reducing breast cancer risk: the largest protective effects were founding women who did not drink or smoke, had never given birth [Friedenreich et al., 2001], or were not using hormone replacement therapy (HRT) [Patel et al., 2003].