Obesity and Breast Cancer Risk
An article published in the November 1st issue of the Journal of Clinical Oncology has somewhat muddled the consensus theory that excessive dietary fat is linked to greater breast cancer risk. Dr. Michelle Holes of Harvard Medical School and Brigham and Women's Hospital in Boston and colleagues studied hormone levels from 381 healthy postmenopausal women in 1989 and 1990. They measured their fat intake through food-frequency questionnaires that the participants previously completed in 1986 and then again in 1990.
They observed that a high-fat diet did not lead to higher plasma levels of estrogen. (High estrogen levels have been associated with an increased risk of breast cancer.) "This result is inconsistent with the hypothesis that fat intake predisposes to breast cancer risk by raising endogenous estrogen levels," they wrote. Even without adjusting for obesity, they noted, the association between dietary fat and estrogen was not significant.
And yet, numerous other studies have linked a high fat diet with an increased breast cancer risk.
A report that received widespread publicity last year concluded that "waist circumference," i.e., abdominal fat, was a risk factor for breast cancer, particularly in postmenopausal women who have never taken hormone replacement therapy.
Writing in the American Journal of Epidemiology, Dr. Zhiping Huang of the Harvard School of Public Health and colleagues examined the association between waist circumference and breast cancer risk in 47,382 women involved in the Nurses' Health Study. Waist and hip measurements were taken in 1986 and the group was followed through 1994.
During the study period, 197 premenopausal women developed breast cancer and 840 postmenopausal women developed the disease. In premenopausal women, the researchers found that "both waist circumference and the waist/hip ratio were positively but not significantly related to risk of premenopausal breast cancer."
However, they found that waist circumference, hip circumference and the waist/hip ratio were "moderately associated" with an increase in breast cancer risk in the postmenopausal women. This association was strongest for postmenopausal women who had never taken hormone replacement therapy.
Huang's team wrote that "abdominal obesity" appears to be associated with increased estradiol, an estrogen which has been linked to increased breast cancer risk.
Similarly, a study led by Dr. Ingrid Hall of the University of North Carolina, Chapel Hill, found a link between waist-to-hip ratio and breast cancer risk in both African-American and Caucasian women.
Writing in the American Journal of Epidemiology, Hall and her colleagues concluded that despite higher general obesity rates for African-American women compared with Caucasian women, overall body size does not appear to increase their relative risk of breast cancer. However, there does seem to be a specific link between an increasing waist-to-hip ratio and a greater risk for the disease.
Hall's team studied the association between numerous physical factors-including waist-to-hip ratio-and the risk of breast cancer. They compared 350 African-American breast cancer survivors with 353 African-American women without the disease, and 523 Caucasian breast cancer survivors with 471 Caucasian women without the disease. All of the women were participants in the population-based Carolina Breast Cancer Study.
After adjusting for body mass index, they found a positive association between breast cancer risk and the waist-to-hip ratio in both premenopausal and postmenopausal women of both races. They wrote that their findings suggest " central fat distribution ... may be an adverse risk factor for breast cancer."
The prevalence of obesity is at an all-time high in the United States and is a particular concern among minority women. Surgeon General Dr. David Satcher recently told the annual meeting of the National Medical Association that as many as 50 percent of African-American women are obese, suggesting that this may be one reason that breast cancer mortality remains higher in African-American women.
According to a study released by the American Obesity Association, healthcare costs for obese adults will exceed $230 billion this year. It is estimated that 22 percent of the total adult population-39 million Americans-meet the criteria for obesity, which includes a body mass index of 30 or greater.
The study analyzed the direct medical costs of treating 15 conditions related to obesity, including breast and other cancers, diabetes, hypertension, heart disease and stroke. The data showed that the direct medical costs of treating obese adults with these associated medical conditions is $102 billion. That figure does not include the cost of treating the obesity itself.
Many studies have suggested that diet can play a major role in cancer prevention. It is estimated that the incidence of 50 percent of certain cancers (including breast, prostate, pancreas, ovary, endometrium, and colon)-and 35 percent of deaths from these cancers-can be directly associated with Western dietary habits. In general, the typical diet in the United States provides only about half the recommended fiber intake and is far too high in calories, especially those which come from fat (certain kinds of which have been shown to enhance the development of cancerous tumors).
To achieve any meaningful risk reductions for breast and certain other cancers, caloric intake must be reduced, nutritionists warn, especially the fat component. The latter should be 20 percent or less of total caloric intake. In addition, fiber should be increased to 25-35 grams per day for adults, especially fiber derived from grains, vegetables, legumes, and fruits.
Such dietary improvements would not only reduce risk levels for cancers and other chronic diseases, but would dramatically throttle the ballooning cost of medical care in the United States.
SOURCES:
Journal of Clinical Oncology, November 1, 2000; 18:3668-3676
American Journal of Epidemiology, December 1999; 150:1316-1324
Cancer, June 2000; 88:2751-2757
American Journal of Epidemiology, April 15, 2000; 151:754-764
Pediatric News, 1999; 33(10):42
American Obesity Association (http://www.obesity.org)
Toxicology Science, December 1999; 52(Supplement 2): 72-86
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