Wednesday, November 20, 2013

Obesity shortening life among breast cancer survivors, national US data

Obesity is a strong driver for postmenopausal breast cancer. Consistent data from around the world show that overweight and obese women are at increased risk of breast cancer through their postmenopausal years. It is estimated that obesity causes more than 10% of postmenopausal breast cancer. Mechanisms for this include higher circulating estrogen levels among overweight and obese women compared to lean women, and insulin pathways. After menopause the ovaries are less active, and fat cells produce estrogen. Obesity is also related to mortality from many other causes (heart disease, stroke, diabetes, etc.). To put the breast cancer burden in context and evaluate the population health impact of breast cancer on lifespan Dr. Chang and colleagues draw on US National Health Interview Survey data and the linked mortality data. They then estimate life expectancy for women who are normal weight and obese, and the life years lost to breast cancer (see report).

The national data show that the life years lost among women diagnosed with breast cancer are greater for younger women than those diagnosed at older ages. This makes good sense. In addition, obese women with breast cancer had greater loss of life than non-obese women. For example, women who were obese and diagnosed with breast cancer before age 50 lost on the average 9.8 years compared to non-obese women who lost 7.8 years. For women diagnosed after age 70 obese women lost approximately 5 years and the nonobese 3.7 years. This pattern was also seen in analysis of African American women.

Choosing measures for evaluation of population level health remains an area that the National Academy of Sciences continues to address. They have recommended life expectancy and quality of life as appropriate measures for population health. This report, evaluating life years lost associated with breast cancer applies this framework. The data clearly support a greater emphasis on the prevention and control of obesity given its impact on this the second most common cause of cancer mortality in women.

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