Does Obesity Increase the Risk of Breast Cancer?

Breast cancer is the most prevalent cancer found in women. The major causes of breast cancer are obesity and overweight.
The effect of obesity on breast cancer risk is based on a woman's menopausal status. Before the end of menstrual cycle, obese women are less exposed to breast cancer than women of a medium weight. Anyways, after menopause, obese women have 1.5 times the risk of women of a healthy weight.
Obese women are also at high risk of dying from breast cancer after menopause compared with bony women. Scientists estimate that about 11,000 to 18,000 deaths per year from breast cancer in US women over age 50 might be avoided if women could maintain a body mass index under 25 through their adult lives (16).
It has been noticed that obesity augments the risk of breast cancer only among postmenopausal women who do not use menopausal hormones. However, there is no significant difference in breast cancer risk between obese women and women of a healthy weight if women belonging to both categories use menopausal hormones.

Obese women have higher amounts of estrogen in their body. Estrogen is mainly produced from the fatty tissues and more amount of fat in your body means you have higher chances of getting affected by breast cancer. Good nutrition, healthy living conditions and a fine environment may help girls to start puberty earlier in life and attain menopause later. Estrogen develops though out the fertility period. And better levels of estrogen in the body increases the risk of breast cancer in women. Before menopause, the primary source of estrogen is the ovaries. However, fat tissue also produces estrogen and, after the ovaries have stopped producing hormones, fat tissue comes to be the most important estrogen source. Estrogen levels in postmenopausal women are 50 to 100 percent higher among heavy compared to lean women. This makes the estrogen-sensitive tissues exposed to more estrogen stimulation in heavy women, which causes a more rapid growth of estrogen-responsive breast tumors.

Another factor related to the higher breast cancer death rates in heavy women is that breast cancer is more likely to be detected at a later stage in obese women than in lean women. This is because the detection of a breast tumor is more difficult in obese versus lean women.
There is some evidence that, among African American women, the risk associated with obesity may be absent or less than that of other populations. However, a recent report showed that African American women who have a high body mass index are more likely to have an advanced stage of breast cancer at diagnosis.

Weight gain during adulthood has been found to be the most consistent and strongest predictor of breast cancer risk in studies in which it has been examined.
The distribution of body fat may also affect breast cancer risk. Women with a large amount of abdominal fat have a greater breast cancer risk than those whose fat is distributed over the hips, buttocks, and lower extremities. Results from studies on the effect of abdominal fat are much less consistent than studies on weight gain or Body Mass Index.