Xu Q1, Esterman A2, Dorrian J3, Warland J1.
Chronobiol Int. 2020 Mar 9:1-13. doi: 10.1080/07420528.2020.1737101. [Epub ahead of print]
We examined whether sunlight affects hot flushes in working menopausal women and explored effect modification by shift work and season. In this prospective cohort study, daily hot flush score (outcome) was measured by the 7-day North Central Cancer Treatment Group Daily Vasomotor Symptoms Diary. Daily duration of sunlight (≥2000 lux) was recorded by the HOBO MX2202 pendant. Both variables were measured in two 7-day data collection phases. T0 data were collected during the Australian Summer (December 2017, January and February 2018); and T1 data were collected in the Australian winter (June, July and August 2018). Linear mixed effects model was used. Shift work and season were both confounders and effect modifiers. To detect a median effect size of R2 = 0.2, 34 women were required to achieve an effective sample size of 41. A total of 49 menopausal women were recruited, 11 shift and 38 day workers. Some 13 women had various missing observations. For shift workers, an hour increase in sunlight exposure was associated with a 1.4-point reduction in hot flush score (p = .016). This relationship was not significant for day workers (p = .185). The finding of this study suggests increased sunlight exposure might improve hot flushes in menopausal shift workers who are moderately bothered by hot flushes, but probably not in day workers. The possible role of shift-work associated circadian disruption on estrogen level in regard to elevated intensity and frequency of hot flush in menopausal women is discussed.