Physical activity and endogenous sex hormones in postmenopausal women: to what extent are observed associations confounded or modified by BMI?
OBJECTIVE
To investigate associations between physical activity and endogenous sex hormones after menopause with a special focus on confounding and effect modification by body mass index (BMI).


METHODS
A cross-sectional study among 1,260 postmenopausal women was conducted. Generalized linear models were used to compare levels of total leisure-time physical activity, sports activities, bicycling, and walking with levels of sex hormones and sex-hormone-binding-globulin (SHBG).


RESULTS
Higher sports activity levels were significantly associated with lower levels of estrone and total and free testosterone in multivariate adjusted models. After additional adjustment for BMI, associations with estrone and free testosterone were attenuated; the association with total testosterone remained unchanged. No physical activity variable was significantly related to total and free estradiol, androstenedione, or SHBG. We did not observe effect modification by BMI.


CONCLUSIONS
Sports activities may lead to lower levels of estrone and testosterone in postmenopausal women. While effects on estrone and free testosterone seem to be largely mediated by BMI, effects on total testosterone appear to be mainly independent of BMI. The BMI-independent effects on these hormones (especially on total testosterone) could at least partly explain why physical activity has been frequently reported to be preventive for postmenopausal breast cancer, even after accounting for BMI.
Unit of Environmental Epidemiology, German Cancer Research Center, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, Heidelberg, Germany.
Stefanie
S
Liedtke
Martina E
ME
Schmidt
Susen
S
Becker
Rudolf
R
Kaaks
Aida Karina
AK
Zaineddin
Katharina
K
Buck
Dieter
D
Flesch-Janys
Jürgen
J
Wahrendorf
Jenny
J
Chang-Claude
Karen
K
Steindorf
D000328:Adult; D000368:Aged; D015992:Body Mass Index; D016022:Case-Control Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D012739:Gonadal Steroid Hormones / Q000097:blood*; D006801:Humans; D008875:Middle Aged; D017698:Postmenopause / Q000502:physiology*; D011863:Radioimmunoassay
D012739:Gonadal Steroid Hormones