Rotating night shift work and mammographic density
Menée sur 640 infirmières âgées de 40 à 60 ans, cette étude transversale évalue l'association entre un travail posté par rotation et la densité mammaire
Background: An increased risk of breast cancer has been observed in night shift workers. Exposure to artificial light at night, disruption of the endogenous circadian rhythm with suppression of the melatonin synthesis have been suggested mechanisms. We investigated the hypothesis that rotating night shift work is associated with mammographic density. Methods:We conducted a cross-sectional study on the association between rotating night shift work characteristics, 6-sulfatoxymelatonin(6MTs) creatinine adjusted in a spot morning urine sample and a computer-assisted measure of mammographic density in 640 nurses and midwives aged 40-60. The associations were evaluated using regression models adjusted for age, BMI, menopausal status, age at menopause, age at menarche, smoking, and the calendar season of the year when mammography was performed. Results:The adjusted means of percent mammographic density and absolute density were slightly higher among women working rotating night shifts, but not statistically significant (percent mammographic density=23.6%, 95%CI: 21.9-25.4% vs. 22.5%, 95%CI: 20.8-24.3%; absolute density=23.9 cm2, 95%CI: 21.4-26.4 cm2, vs. 21.8 cm2, 95%CI: 19.4-24.3 cm2 in rotating night shift and day shift nurses, respectively). There were no significant associations between the current or cumulative rotating night shift work exposure metrics and mammographic density. No association was observed between morning MT6s and mammographic density. Conclusions:The hypothesis on the link between rotating night shift work, melatonin synthesis disruption and mammographic density is not supported by the results of the present study. Impact:It is unlikely that the development of breast cancer in nurses working rotating night shifts is mediated by an increase in mammographic density.