Body Fat, Hormones and Breast Cancer
Body Fat, Hormones and Breast Cancer
Breast Cancer Obesity is a known risk factor for breast cancer. Excess weight increases the risk of being diagnosed with breast cancer, and is associated with higher grade tumors and poorer survival after diagnosis.1-4 Body fat is now recognized as more than just extra stored energy; it is an active endocrine organ. Fat tissue produces hormones and other chemical messengers that affect other areas of the body and promote cellular events leading to chronic diseases like heart disease, diabetes and cancer.
Fat tissue, since it produces estrogen, increases the body’s exposure to the hormone. More body fat means higher estrogen levels, and weight loss is known to decrease circulating estrogens in women. Higher cumulative estrogen exposure is another known factor linked to increased breast cancer risk. Estrogen fuels the growth and proliferation of breast cancer cells, and weight loss is hypothesized to reduce the ability of tumors to grow. Estrogen is not the only hormone involved in the relationship between obesity and breast cancer. Excess fat also leads to insulin resistance, and high insulin levels also fuel cancer cell proliferation. High levels of insulin in the blood are thought to be the reason that diabetes increases cancer risk. Also, levels of circulating free IGF-1, another hormone associated with increased cancer risk, tends to be higher in obese subjects. Leptin, another hormone produced by fat tissue (which is higher in those who are overweight), also promotes proliferation of breast cancer cells. With obesity, there is a reduction in the hormone adiponectin produced by fat cells; adiponectin normally enhances insulin sensitivity. Excess fat tissue also promotes a state of inflammation in the body, and many fat-produced inflammatory molecules promote the survival, growth or proliferation of cancer cells or promote cancer indirectly by increasing estrogen synthesis.4,5
Gaining weight during adulthood, even in small, gradual amounts, adds up over time to increase risk. One study evaluated weight gain starting at age 20, and concluded women who gained approximately one pound per year (based on change in BMI) had an 88 percent increase in breast cancer risk in their 50s compared to women whose weight remained stable. Importantly, the researchers noted that this amount of weight gain was common; more than half of the women in the study had gained that much weight since their 20s.6 Although there is agreement that weight gain increases risk, studies are now beginning to ask whether abdominal obesity is more dangerous than overall obesity when it comes to breast cancer. In the context of diabetes and cardiovascular disease, there is evidence that visceral fat—the fat around the organs in the abdominal area—is more pro-inflammatory and confers greater risk than subcutaneous fat.7
Early data had associated waist to hip ratio—an indicator of abdominal obesity—with increased risk of breast cancer.8 In one recent study, instead of asking women how much weight they had gained during adulthood, they asked women in their 50s what size skirt they wore at age 25, and what size they wear now. They found that an increase of one size (e.g., size 8 to size 10) over the course of 10 years produced a 33 percent increase in the risk of postmenopausal breast cancer. In this study, skirt size was a better predictor of breast cancer risk than BMI, implying that visceral fat could be especially hazardous.9 Another study evaluated waist circumference and BMI, and concluded that excess weight increases risk regardless of body shape.10 A third study measured fat mass in different parts of the body. In this study, fat mass in the abdominal area, in each leg and in the whole body were all associated with increased breast cancer risk, though the abdominal area was associated with the greatest increase in risk.11
The overall message from this research is that although visceral fat may be especially dangerous, excess fat, no matter where it is on the body, increases the risk of breast cancer. Obtaining and maintain a favorable weight and a healthful, nutrient rich diet is not merely for looking good and feeling well, it is imperative for your future health. Maintaining a healthy weight throughout adulthood is one of the most important preventive measures women can take to reduce breast cancer risk. A diet of high-nutrient foods fights breast cancer from all angles, helping to prevent weight gain while also keeping insulin levels in a healthy range and providing anti-inflammatory and anti-cancer phytochemicals.
We can win the war on breast cancer right now and save millions of women’s lives. Not with more research for new drugs, or with wearing pink for “breast cancer awareness” but instead with a change in the way Americans eat. This needs to happen right now across America, and you can help yourself and others.
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