Seasonality of reproductive function and weight loss in rural Nepali women.

Menstrual and hormonal disturbances have been reported in thin, dieting and exercising Western women, and also recently in rural African women. A study of salivary progesterone profiles was undertaken in a Nepali population to examine whether seasonal increases in workload and changes in energy balance influenced ovarian function. Women's energy expenditure levels were moderately heavy in the winter and very heavy in the monsoon, and body mass fluctuated by -2.8 to +4.8 kg. Samples were collected from 24 normally menstruating women in two seasons, each individual serving as her own control. Progesterone levels were significantly depressed in the monsoon relative to winter for women who lost weight, but not for women who gained weight, indicating that energy imbalance is associated with a loss of fecundity. No differences in body mass index were found between women who lost or gained weight. Progesterone levels were age-dependent, and the degree of hormonal disturbance between age-groups was related to weight loss. The study demonstrates seasonal changes in the fecundity of hard-working Nepali women and a direct link between ovarian function and weight loss (negative energy balance), which is independent of current nutritional status.