Relationship of body composition measures and menstrual cycle length.

Menstrual cycle disruption has been observed in women with low body weight due to anorexia nervosa, or to athletics. However, the association of the full range of body composition measures with cyclicity has not been determined. Therefore, the purpose of this study was to determine the strength and direction of association between body composition measures (Quetelet Index, body fat mass, and body lean mass) and menstrual cycle length. Menstrual cycle diaries were distributed to women aged 24-45 in the Michigan Bone Health Study beginning in 1992. A total of 4392 menstrual cycles from 436 women were analysed from the first year of this ongoing study. Body composition measures (Quetelet Index or body mass index (kg/m2), body fat mass and body lean mass (kg) were obtained at annual clinic visits by means of dual-energy X-ray absorptiometry (DEXA). Mixed-model analyses were used to determine the degree of association between menstrual cycle length and body composition measures, controlling for age. There was a significant positive association with cycle length for each body composition measure. The relationship between each body composition measure and cycle length was nonlinear with the longest mean cycle lengths occurring with greater BMI, body fat mass or body lean mass. Longer cycle length was also noted at the lowest levels of BMI and body fat mass. These results may account for the purported later age at menopause for obese women.