Environmental Exposures and Female Reproductive Aging

Abstract

Reproductive aging is one of the major determinants of fertility and can profoundly affect women’s health and well-being in later life. Epidemiological studies have identified external factors related to reproductive aging, but evidence was still scarce for environmental exposures. In this dissertation, we sought to examine associations of exposure to different environmental factors with markers of reproductive aging in a large, prospective, nationwide female cohort. In chapters 1 and 2, we examined associations of exposure to particulate air pollution, traffic, noise, and outdoor light at night in midlife with the timing of natural menopause in the Nurses’ Health Study II. Our results suggested women with higher residential particulate matter exposure and women who lived closer to major roadways after age 40 had slightly earlier onset of menopause. Meanwhile, no associations were observed for noise and outdoor light at night with menopausal age. We further investigated whether exposure to solar ultraviolet (UV) radiation, an essential environmental factor in dermal vitamin D conversion, can delay menopause in chapter 3. In addition to exposure in midlife, we also considered UV exposure in early life in this analysis. Results from this study showed a suggestive trend of later menopause with higher residential UV at age 30 and after age 40, but no associations were found for UV exposure at birth and at age 15. These studies added important evidence for understanding the associations of environmental factors with reproductive aging. Most studies on environmental exposures only considered the individual association by each exposure, while the joint association of a complex mixture of environmental factors were understudied. In chapter 4, we used the advanced mixture analysis methods to estimate the overall association of multiple environmental factors (i.e., surrounding greenness, air pollution, noise, outdoor light at night, UV, and air toxics) with anti-Müllerian hormone (AMH), a marker of ovarian reserve. Results from different mixture methods consistently showed negative joint associations of these exposures with AMH, in which ambient formaldehyde and benzene were the key exposures. Overall, this dissertation evaluated the associations of environmental factors and female reproductive aging, an important topic in women’s health. Our findings indicated the need for further evidence in this topic.