Academic journal article Scandinavian Journal of Work, Environment & Health

Night Shift Work and Other Determinants of Estradiol, Testosterone, and Dehydroepiandrosterone Sulfate among Middle-Aged Nurses and Midwives

Academic journal article Scandinavian Journal of Work, Environment & Health

Night Shift Work and Other Determinants of Estradiol, Testosterone, and Dehydroepiandrosterone Sulfate among Middle-Aged Nurses and Midwives

Article excerpt

Sex hormones that serve essential functions in women's physiology are also known to play a role in the etiology of common diseases such as osteoporosis and bone fractures (1), breast cancer (2, 3), and cardiovascular diseases (1). Both experimental and observational studies confirmed the role of estrogens in the etiology of breast cancer (4). Strong epidemiological evidence for the association between circulating estrogens and breast cancer was established among postmenopausal women, although this relationship was less convincing among premenopausal women (5, 6). Also, increased circulating concentrations of dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulphate (DHEAS) and testosterone were associated with breast cancer risk among women (5, 7). A pooled analysis of data performed by the Endogenous Hormones and Breast Cancer Collaborative Group provided strong evidence that plasma sex hormone levels predict breast cancer risk (2, 7), and the Breast Cancer Prevention Collaborative Group recommends measuring these hormones in plasma to assess the risk of breast cancer (8).

Shift work causing circadian disruption was linked to the risk of breast cancer, and the International Agency for Research on Cancer (IARC) has classified night shift work which disrupts the circadian rhythm as probably carcinogenic to humans (9). Working at night and exposure to artificial light at night have been proposed as potent circadian rhythm disruptors (10), which could contribute to physiological disturbances and - in a long run - to the etiology of various chronic diseases. There have also been a number of epidemiological studies focusing on an association between night shift work and breast cancer risk. The most recent meta-analysis based on 16 epidemiological studies reported a 9% increase in breast cancer risk per five years of night work based on case-control but not cohort studies (11). Still the most recent cohort study in Sweden showed breast cancer risk that increased by 77% among long-term female night workers (12).

One of the proposed mechanisms underlying the increased risk of breast cancer among night shift workers was a decrease in melatonin level and an increase in reproductive hormone synthesis in response to light-at-night (13). Moreover, night workers were more likely than day workers to become obese (14, 15) and to have unhealthy lifestyle (16) such as smoking (17), unhealthy diet (16) or low physical activity (18), which may contribute to the risk of cancer and affect hormonal milieu and sex hormone metabolism (19, 20).

There has been a limited number of observational studies examining the potential alterations in sex hormones or their precursor DHEA among women working night shifts (13, 21-27). In a study investigating the association between the duration of night shift work and estradiol level among 663 postmenopausal women, a significant positive relationship was found (21). Another study among postmenopausal women, comparing hormones among those who ever worked graveyard versus those working during the days (25), did not reveal differences, although the number of women classified as night workers who ever worked the graveyard shift was small (N=7). No statistically significant difference in estradiol level by night shift work status among postmenopausal women was noted in the study from Spain, but adjusted mean of estradiol was higher among night than day workers (24.3 pg/ml versus 15.04 pg/ml) (27). Two recent analyses have shown a positive link between estradiol and night work among premenopausal women when the hormone was measured in the follicular phase (24, 27) or when the analysis was adjusted for the menstrual phase (27). Statistically significant associations between the duration of night shift work and estradiol were observed in crude analysis among 82 Canadian premenopausal nurses with mean night work history of 11 years but not in an adjusted analysis (23). Another study among premenopausal nurses (N=79) selected from NHSII cohort showed no association between the number of night duties during two weeks before blood draw and estradiol, testosterone and DHEAS concentrations, but the majority of nurses in this study (82%) reported no night duties during this period (21). …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.