RELATIONSHIP OF BODY-COMPOSITION MEASURES AND MENSTRUAL-CYCLE LENGTH

Menstrual cycle disruption has been observed in women with low body we ight due to anorexia nervosa, or to athletics. However, the associatio n of the full range of body composition measures with cyclicity has no t been determined. Therefore, the purpose of this study was to determi ne the strength and direction of association between body composition measures (Quetelet Index, body fat mass, and body lean mass) and menst rual cycle length. Menstrual cycle diaries were distributed to women a ged 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/m(2)), body fat mass and body lean mass (kg)) w ere obtained at annual clinic visits by means of dual-energy X-ray abs orptiometry (DEXA). Mixed-model analyses were used to determine the de gree of association between menstrual cycle length and body compositio n measures, controlling for age. There was a significant positive asso ciation with cycle length for each body composition measure. The relat ionship between each body composition measure and cycle length was non linear with the longest mean cycle lengths occurring with greater BMI, body fat mass or body lean mass. Longer cycle length was also noted a t the lowest levels of BMI and body fat mass. These results may accoun t for the purported later age at menopause for obese women.