DIETARY-FAT AND SPORTS ACTIVITY AS DETERMINANTS FOR AGE AT MENARCHE

A prospective study (1985-1991) was conducted to evaluate the role of nutrition, physical activity, and other life-style factors for the age at menarche, a known breast cancer risk factor. In 1988-1989, a total of 261 girls, aged 8-15 years, from a nationwide representative nutri tion and activity survey (1985-1988) responded additionally to a maile d questionnaire on personal maturation and anthropometric data, physic al activity, and information about nutritional habits, measured by a s hort food-frequency questionnaire. All girls without menarche at the t ime of questionnaire mailing were observed for 2 years or until the ev ent of menarche. At the end of the follow-up period, 79% of the girls had experienced menarche. The survey and questionnaire data were analy zed for their relation to age at menarche using Cox's proportional haz ards method. After excluding participants with largely deviating measu rements between survey and questionnaire, the increased energy-adjuste d fat intake was associated with accelerated menarche (relative risk = 2. 1; 95% confidence interval 1.1-4.0; lowest vs. highest quartile), while increased sports activity was associated with a delay in menarch e (relative risk = 0.3; 95% confidence interval 0.1-0.5; lowest vs. hi ghest quartile). Parameters of physical development such as body weigh t or body fatness were found to be predictors of menarche. The study p rovides evidence that dietary effects on breast cancer risk might be i ndirect by influencing hormonal events like the age at menarche.