Hum. Reprod. Advance Access published online on July 18, 2008
Human Reproduction, doi:10.1093/humrep/den213
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Body fat, energy balance and estradiol levels: a study based on hormonal profiles from complete menstrual cycles
1 Institute of Anthropology, Polish Academy of Science, Kuznicza 35, 50-951 Wroclaw, Poland 2 Department of Epidemiology and Population Studies, Jagiellonian University, Collegium Medicum, 31-531 Krakow, Poland 3 Department of Anthropology, Harvard University, Cambridge, MA 02138, USA 4 Institute of Community Medicine, University of Tromso, N-9037 Tromso, Norway 5 The Cancer Center, Ulleval University Hospital, N-0407 Oslo, Norway
6 Correspondence address. Institute of Anthropology, Polish Academy of Science, Kuznicza 35, 50-951 Wroclaw, Poland. E-mail: annaz{at}antro.pan.wroc.pl
BACKGROUND: Female fecundity is regulated by nutritional status. Although widely cited, this hypothesis is not strongly supported by empirical data from non-obese, healthy women of reproductive age.
METHODS: Healthy, reproductive aged women (n = 141) from Southern Poland collected daily morning saliva samples for one complete menstrual cycle. Levels of 17-β-estradiol were analyzed by radioimmunoassay. Anthropometric measurements, including body fat percentage, were taken randomly with respect to phase of the menstrual cycle. Energy balance was specified based on changes in body fat percentage from the beginning to the end of the observation period.
RESULTS: Women with very low and high body fat had significantly lower levels of E2 compared with women with low and average body fat. In women of very low to average body fat, a 10% increase in body fat was associated with a 5–7 pmol/l increase in estradiol levels. The association between fat percentage and E2 was even stronger in women with positive energy balance, who also showed significant differences between body fat groups in estradiol profiles across whole the menstrual cycle. No such relationship was found in women with negative energy balance.
CONCLUSIONS: In healthy women, we found a non-linear association between body fat and estradiol levels. Both very low and high body fat was associated with decreased estradiol levels. The relationship between estradiol and body fat was strongly influenced by women’s energy balance.
Key words: 17-β-estradiol/body fat percentage/energy balance/menstrual cycle
Submitted on October 4, 2007; resubmitted on March 20, 2008; accepted on April 8, 2008.