Seasonality of reproductive function and weight loss in rural Nepali women

Abstract

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.

PIP: In October-November 1990 and August-September 1991, anthropologists collected saliva samples from 24 17-46 year old nonpregnant, nonlactating, and normally menstruating Tamang women in a remote village in the foothills of the Himalayas in northwestern Nepal to measure progesterone levels (indicative of ovarian function). They used these levels to determine whether a very heavy workload during the monsoon season and changes in dietary intake affected ovarian function. Anthropometric measurements were also taken. The women served as their own controls. Seasonal changes in body mass ranged from -2.8 kg to 4.8 kg. Mean and mid-luteal progesterone levels fell 27% (104-76 pmol/l) and 38% (138-85 pmol/l), respectively, between the winter and monsoon (p .01). The levels of ovarian function were much lower than those of healthy, regularly menstruating Western women and of menstruating Lese women of the Ituri forest in Zaire (mean luteal phase progesterone levels, 104 pmol/l vs. 232 pmol/l for Boston women and 140 pmol/l for Lese women). Reduction in progesterone levels was most significant for 24-34 year old women. In fact, the reduction in mid-luteal progesterone levels was only significant in this age group (p .05). Body mass index did not influence progesterone levels, regardless of changes in weight or age. Reduced progesterone levels was only significant for women who lost weight between the winter and the monsoon seasons, suggesting that energy imbalance is linked to loss of fecundity. Younger women were more likely to gain weight than older women (.6 kg vs. -1.1 kg for middle aged women and -.2 for older women; p .05). The regression between changes in progesterone levels and degree of weight loss was also significant (p .01). Between the winter and the monsoon, the percentage of ovulatory cycles decreased from 71 to 38%. These findings showed seasonal changes in the fecundity of these women and a direct association between ovarian function and weight loss, regardless of current nutritional status.