Thinness in Japanese Young Women

Abstract

To the Editor: The desire to be thin is widespread among young women. In some European countries, fashion models are required to have a body mass index (BMI; weight [kg]/height2 [m2]) of 18 kg/m2 or greater to discourage severe emaciation.1 Unhealthy dietary regimens for weight loss during youth can lead to unfavorable outcomes, including eating disorders2 or low bone mineral content,3 in adulthood. Asian young women, especially Japanese women, have been reported to strongly desire to be thin, even though they have a lower BMI than other ethnic groups.4 In Japan, more than 20% of women in their 20s are underweight (BMI <18.5 kg/m2),5 a percentage much higher than in most developed countries. In the United States, the prevalence of obesity continues to rise among children, adolescents and adult men, but not women.6 The BMI physiologically increases throughout life after approximately 6 years of age.7 We compared BMI curves by age among young people from Japan, Korea, and the United States. We also examined the period during which unhealthy emaciation began in Japanese women. We performed an ecologic study, using national health statistics from the United States (NHANES 2003–2004 and 2005–2006), Korea (KNHANES 2005), and Japan (NNS-J 1957–2006). We calculated BMI, using information on height and weight from these databases and compared the BMI curves from age 10 to 29 years among men and women in the 3 countries. We also chronologically rearranged cross-sectional data on Japanese women according to birth year. Mean BMI for men and women in the United States increased with age, as it did for men in Korea and Japan; however, the increase was not as steep for Asian men as for US men and women (Fig. 1). The increase in Korean women stopped at around 18 years of age and remained constant thereafter, whereas in Japanese women, the BMI started to decrease at approximately age 18 years.FIGURE 1.: Cross-sectional relationship between age and BMI in young men and women in the United States (2003–2006), Korea (2005), and Japan (2003–2005).Data according to period of birth (Fig. 2) showed no tendency toward leanness among Japanese women born between 1945 and 1949 (age 59–63 in 2008); the curve was similar to that of Korean women born during this time. However, the BMI of those born between 1950 and 1954 (age 54–59 in 2008) sharply dropped after the age of about 20 years. Then, in those born between 1955 and 1959 (age 49–53 in 2008), the drop in BMI began at age around 15 years and, in subsequent 5-year period, the magnitude of decline intensified. Thus, leanness among Japanese young women (late teens–early 20s) became apparent in the 1970s. The curves for BMI before the age of 15 years were similar regardless of the period of birth.FIGURE 2.: Longitudinal changes in BMI in young Japanese women between the age of 10 and 29 years, depending on birth year.In the 1970s, during the period when decreases in BMI became evident, Japan experienced an economic growth spurt similar to that currently being experienced in other Asian countries. Lifestyle and cultural changes, including vast exposure to media, might have fostered the desire of women to be thin. At present, a reduction in mean BMI among young women has not been reported in other countries, despite the widespread desire to be thin.4 Most concerns today are with increasing BMI. This should not overshadow concerns about possible declines in BMI among young women. The social background or rationale for this apparently nonphysiologic drop in BMI among Japanese women may be useful in addressing this issue in other developed countries. ACKNOWLEDGMENTS The authors thank Young Seol Kim and Sang Youl Rhee from the Kyung Hee University for providing assistance in the acquisition of the Korean data. Supported in part by the Japanese Ministry of Health, Labor and Welfare, as well as the Japan Society for the Promotion of Science. Ayumi Sugawara Kazumi Saito Mutsumi Sato Satoru Kodama Hirohito Sone Department of Lifestyle Medicine Ochanomizu University Tokyo, Japan, [email protected]