Thursday, December 17, 2015

A Closer Look at Obesity, Breast Cancer, and Health Disparities

by Graham Colditz, MD, DrPH

Obesity is an established cause of postmenopausal breast cancer, with the International Agency for Research on Cancer (IARC) estimating that approximately 10 percent of postmenopausal breast cancer is due to excess weight (1). Overweight and obesity also increase the risk of mortality after diagnosis. One large analysis combining data from some 82 studies found that women who were obese in the months before being diagnosed had around a 40 percent higher risk of breast cancer mortality and total mortality compared to normal weight women (see Figure 1) (2).
Figure 1

Weight gain

Most women who are overweight or obese gain their weight predominantly in the adult years. We assessed the relation between adult weight gain and postmenopausal breast cancer after 26 years of follow-up in participants in the Nurse’s Health Study (3). Women who gained 22 pounds or more after menopause experienced an approximately 20 percent greater risk of breast cancer than women who maintained their weight after menopause. We also observed that weight gain of 5 pounds or more from age 18 on accounted for 15 percent of all postmenopausal breast cancer.

Though substantial weight gain is often something that happens over a relatively prolonged period, in the Nurses’ Health Study, we also assessed the potential impact of short-term recent weight gain on breast cancer risk (4). We looked at weight gain over 4 years, and the risk of cancer in the next 2 years. We found that short term weight gain increased the risk of premenopausal breast cancer, and that these risks were significant for two specific types of disease: ER+/PR- breast cancer and ER-/PR- breast cancer (see Figure 2). Compared to women who didn’t gain weight, the risk of ER+/PR- breast cancer was more than doubled with each 25 pounds gained over that period.

Figure 2

Why does this matter? Substantial weight gain in premenopausal years increases the risk of hard to treat breast cancer, such as ER-/PR- disease, and also conveys future cancer risk as women pass through into the postmenopausal years 4. While weight loss after menopause can substantially reduce breast cancer risk, perhaps by up to a half (see Figure 3) (3), avoiding weight gain is clearly preferable. Weight, once put on, can be hard to lose, and maintaining a lifelong healthy weight has the added benefits of improving quality of life and lowering the risk of many other cancers as well as other serious diseases, like diabetes, heart disease, stroke, and osteoporosis (5).
Figure 3

Prevalence and disparities in weight status

Weight gain, unfortunately, is a very common problem in the United States, and it is not one borne equally across society (6). While black and white boys show similar weight distribution from ages 5 to 17, black and white girls differ in weight starting around age 9, with black girls on average heavier than white girls. This difference continues to increase through age 17.

Weight gain through childhood and adolescence may reflect external circumstances – which can include factors like affordability of healthy food choices, availability of safe places to play/exercise, exposure to marketing of unhealthy foods, and parent/guardian time-constraints (7,8).

And many of the disparities in weight distributions in youth – and the social and physical environmental factors that help contribute to them – continue through the adult years.

Our recent analysis of national United States data (National Health and Nutrition Examination Survey) shows that African American women have had an overall higher prevalence of overweight and obesity compared to non-Hispanic white women over the past 20 years (see Figure 4) (9). The data also show that the prevalence of overweight and obesity in African American women exceeds that of non-Hispanic white women when looking at adults under age 50 and age 50 and over (see Figure 5). To be heavier as a group before age 50 implies continuing excess weight gain through the premenopausal years.

Figure 4 - Overall changes in weight status over the past 20 years. Source: Yang and Colditz, 2015

Figure 5 - Weight status by age – under age 50, age 50 and over. Source: Yang and Colditz, 2015

In a recent paper in the American Society of Clinical Oncology’s ASCO Post , I wrote about the excess rate of hard to treat breast cancers in African American women and that such hard to treat tumors are one likely reason that African American women experience higher rates of breast cancer mortality than do non-Hispanic white women. And growing data, already discussed, suggest that unhealthy weight may be a contributor to the risk for such hard to treat cancers.

So, while overweight is a key driver of breast cancer risk and poorer outcomes for all women, particular emphasis is needed on efforts that narrow the weight status and health disparities seen between races and ethnicities, improving outcomes across the board.

To successfully tackle the issue of overweight in such a way will require political will and multidisciplinary efforts that are focused not just on individual behaviors but also on the important physical, social, and healthcare environments that can be key barriers to or facilitators of individual actions on diet and physical activity.

It is a tall order but one certain to pay off many times over.


References

1. International Agency for Research on Cancer. Weight Control and Physical Activity. Vol 6. Lyon: International Agency for Research on Cancer; 2002.

2. Chan DS, Vieira AR, Aune D, et al. Body mass index and survival in women with breast cancer-systematic literature review and meta-analysis of 82 follow-up studies. Ann Oncol. 2014.

3. Eliassen AH, Colditz GA, Rosner B, Willett WC, Hankinson SE. Adult weight change and risk of postmenopausal breast cancer. JAMA. 2006;296(2):193-201.

4. Rosner B, Eliassen AH, Toriola AT, et al. Short-term weight gain and breast cancer risk by hormone receptor classification among pre- and postmenopausal women. Breast Cancer Res Treat. 2015;150(3):643-653.

5. Willett WC, Dietz WH, Colditz GA. Guidelines for healthy weight. The New England journal of medicine. 1999;341(6):427-434.

6. Rosner B, Prineas R, Loggie J, Daniels SR. Percentiles for body mass index in U.S. children 5 to 17 years of age. J Pediatr. 1998;132(2):211-222.

7. Swinburn BA, Sacks G, Hall KD, et al. The global obesity pandemic: shaped by global drivers and local environments. Lancet. 2011;378(9793):804-814.

8. Blumenthal SJ, Hoffnagle EE, Leung CW, et al. Strategies to improve the dietary quality of Supplemental Nutrition Assistance Program (SNAP) beneficiaries: an assessment of stakeholder opinions. Public Health Nutr. 2014;17(12):2824-2833.

9. Yang L, Colditz GA. Prevalence of Overweight and Obesity in the United States, 2007-2012. JAMA Intern Med. 2015.

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