Abstract
Background. The role of exogenous estrogen use in racial differences in insulin-like growth factor-I (IGF-I) levels which affect cancer risk is unclear. We investigated whether the relationship between race and circulating bioactive IGF-I proteins was mediated by exogenous estrogen and the extent to which exogenous estrogen influenced the race-IGF-I relationship in postmenopausal women. Methods. This cross-sectional study included 636 white and 133 African American postmenopausal women enrolled in an ancillary study of the Women's Health Initiative Observational Study. To assess exogenous estrogen use (nonusers [n = 262] vs users [n = 507]) as a mediator of the race-IGF-I relationship, we used the Baron-Kenny method and an estimation of the proportional change in the odd ratios for IGF-I levels on race plus a bootstrapping test for the significance of the mediation effect. Results. Compared with white women, African American women were more likely to have high IGF-I levels and less likely to use exogenous estrogen. After accounting for race, estrogen nonusers had higher IGF-I levels than estrogen users did. Among oral contraceptive ever users, exogenous estrogen had a strong mediation effect (67%; p =. 018) in the race-IGF-I relationship. In the women with a history of hypertension, exogenous estrogen explained racial differences in IGF-I levels to a modest degree (23%; p =. 029). Conclusions. Exogenous estrogen use has a potentially important role in disparities in IGF-I bioactivity between postmenopausal African American and white women. A history of oral contraceptive use and hypertension may be part of the interconnected hormonal pathways related to racial differences in IGF-I levels.
Original language | English (US) |
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Pages (from-to) | 495-502 |
Number of pages | 8 |
Journal | Journals of Gerontology - Series A Biological Sciences and Medical Sciences |
Volume | 70 |
Issue number | 4 |
DOIs | |
State | Published - Apr 1 2015 |
Keywords
- Exogenous estrogen
- Insulin-like growth factor-I
- Mediation
- Postmenopausal women
ASJC Scopus subject areas
- Aging
- Geriatrics and Gerontology