Night Shift Work and Hormone Levels in Women
Menée auprès de 172 infirmières travaillant de nuit et 151 infirmières travaillant de jour et agées de 20 à 49 ans, cette étude analyse l'association entre un travail de nuit, le niveau d'hormones reproductives et le risque de cancer du sein ainsi que d'autres cancers
Background: Nightshift work may disrupt the normal nocturnal rise in melatonin, resulting in increased breast cancer risk, possibly through increased reproductive hormone levels. We investigated whether nightshift work is associated with decreased levels of urinary 6-sulfatoxymelatonin, the primary metabolite of melatonin, and increased urinary reproductive hormone levels. Methods:Participants were 172 nightshift and 151 dayshift-working nurses, aged 20-49, with regular menstrual cycles. Urine samples were collected throughout work and sleep periods and assayed for 6-sulfatoxymelatonin, LH, FSH, and E1C. Results:6-sulfatoxymelatonin levels were 62% lower and FSH and LH were 62% and 58% higher, respectively, in nightshift-working women during daytime sleep compared to dayshift-working women during nighttime sleep (p≤0.0001). Nighttime sleep on off nights was associated with 42% lower 6-sulfatoxymelatonin levels among the nightshift workers, relative to the dayshift workers (p<0.0001); no significant differences in LH or FSH were observed. 6-sulfatoxymelatonin levels during night work were approximately 69% lower and FSH and LH were 35% and 38% higher, compared to dayshift workers during nighttime sleep. No differences in E1C levels between night and day shift workers were observed. Within nightshift workers, 6-sulfatoxymelatonin levels were lower and reproductive hormone levels were higher during daytime sleep and nighttime work, relative to nighttime sleep (p<0.05). Conclusions:These results indicate nightshift workers have substantially reduced 6-sulfatoxymelatonin levels during night work and daytime sleep, and that levels remain low even when a nightshift worker sleeps at night. Impact:Shift work could be an important risk factor for many other cancers in addition to breast cancer.