RELATIVE WEIGHT, WEIGHT CHANGE, HEIGHT, AND BREAST-CANCER RISK IN ASIAN-AMERICAN WOMEN

Background: Breast cancer incidence rates have historically been four to seven times higher in the United States than in China or Japan, alt hough the reasons remain elusive. When Chinese, Japanese, or Filipino women migrate to the United States, their breast cancer risk rises ove r several generations and reaches that for white women in the United S tates, indicating that modifiable exposures are involved. In a previou s report on this case-control study of breast cancer in Asian-American women, designed to take advantage of their diversity in risk and life style, we demonstrated a sixfold gradient in risk by migration history , comparable to the international differences in breast cancer inciden ce rates. Purpose: In this analysis, we have examined the roles of adu lt height, adiposity, and weight change in breast cancer etiology. Met hods: A population-based, case-control study of breast cancer was cond ucted among women of Chinese, Japanese, and Filipino ethnicities, aged 20-55 years, living in San Francisco-Oakland (CA), Los Angeles (CA), and Oahu (HI) during the period from April 1, 1983, through June 30, 1 987. We successfully interviewed 597 (70%) of 852 eligible case subjec ts and 966 (75%) of 1287 eligible control subjects from August 1985 th rough February 1989. Subjects were asked about current height, usual a dult weight, and usual weight in each decade of life, excluding the mo st recent 3 years and any periods of pregnancy. Results: Height, recen t adiposity (weight in the current decade of life/height(1.5)), and re cent weight change (between the current and preceding decades of life) were strong predictors of breast cancer risk after adjustment was mad e for accepted breast cancer risk factors. Risk doubled (relative risk [RR] = 2.01; 95% confidence interval [CI] = 1.16-3.49) over the 7-inc h (17.8-cm) range in height (two-sided P for trend = .003), with compa rable effects in both premenopausal and postmenopausal women. Except f or reduced risk in the heavy, younger women (weight/height(1.5) > 29 k g/m(1.5) and < 40 years old), risk was positively associated with usua l adult adiposity. Trends in risk became more striking as adiposity in each succeeding decade of adult life was considered. Women in their 5 0s and in the top quintile of adiposity for their age group had twice the breast cancer risk (RR = 2.13; 95% CI = 1.17-3.87) of women in the bottom quintile (two-sided P for trend = .004). Women in their 50s, a bove the median adiposity for their age group, and with a recent gain of more than 10 pounds had three times the risk (RR = 3.01; 95% CI = 1 .45-6.25) of women below the median adiposity and with no recent weigh t change. Recent weight loss was consistently associated with reduced risk (RRs of approximately 0.7) relative to no recent weight change. C onclusions: Adult adiposity, weight change, and height are critical de terminants of breast cancer risk. Increased adiposity and weight gain in the decade preceding diagnosis are especially influential, suggesti ng that excess weight may function as a late stage promoter, Implicati ons: Weight maintenance and/or reduction as an adult, possibly accompa nied by specific changes in diet and physical activity, may have a sig nificant and rapid impact on breast cancer risk.