Light exposure and stress in pregnancy: Effects of blue-blocking glasses on sleep, mood and melatonin

Abstract

Background and Objective: Sleep disturbances are common during pregnancy, with an increasing prevalence in the third trimester. Insomnia is the most frequent sleep disorder reported by 62% of pregnant women. Poor sleep quality and insomnia may influence both the maternal and fetal health, and are associated with preeclampsia, elevated serum glucose, depression, prolonged labour, caesarean birth, intrauterine growth restriction and preterm birth.

Light exposure in the evening and at night has an acute alerting effect, can reduce evening and night sleepiness, may suppress melatonin excretion, and are also associated with later bedtime and shorter sleep time.

Sleep is closely linked to the circadian rhythm and light is the most important zeitgeber entraining the circadian system. Darkness allows production of melatonin, a hormone which regulates the circadian rhythm, and induce sleep. Suprachiasmatic nucleus is the master clock in the brain and controls the circadian rhythm of melatonin synthesised in the pineal gland. Evening and night-time exposure to light of short wavelength, blue light, supresses the melatonin production, delay the circadian rhythms and inhibit sleep.

There is a need of effective and safe non-pharmacological treatments for sleep disturbances in pregnancy. Blue blocking glasses (BB-glasses) may represent such an intervention, by preventing alertness, improve sleep and maintain the melatonin production.

The objective for this thesis was to investigate sleep patterns, sleep behaviour, perceived stress, prevalence of insomnia and evening light exposure in women in the third trimester. Furthermore, the study aimed to investigate the effect of wearing BBglasses in the evening and at night, on sleep outcomes and melatonin profile.

Methods: This thesis is based on a sample of healthy nulliparous women in the third trimester of the pregnancy who were included in a double blind randomized controlled trial conducted at the University of Bergen, Norway. The study lasted for three weeks, where the first week was a baseline week, followed by two weeks of intervention. The intervention comprised orange tinted BB-glasses. The control condition consisted of grey partial blue-blocking control glasses. In both conditions the glasses were worn three hours before bedtime.

Paper 1 was an observational study of 61 pregnant women, using data from the baseline week, and compared with data of sleep and light exposure from 69 nonpregnant female students. The aim of this first paper was to assess sleep pattern, sleep behavior, prevalence of insomnia and evening light exposure in the pregnant women and compare the data with those in the non-pregnant group. Further, Paper 1 aimed to investigate how perceived stress and evening light exposure were associated with sleep outcomes among the pregnant women. Sleep was measured by actigraphy, sleep diaries and the Bergen Insomnia Scale. Stress was assessed by the Relationship Satisfaction Scale, the Perceived Stress Scale and the Pre-Sleep Arousal Scale. Total white light exposure three hours prior to bedtime was measured by wrist-worn actigraphy.

Questionnaires measured sleep, insomnia, and stress. Actigraphy monitored sleep and light exposure.

Papers 2 and 3 present the results from a randomizes controlled trial, including 60 healthy nulliparous women in the third trimester of the pregnancy.

In Paper 2 the main aim was to evaluate the effect of blocking the blue light in the evening and night on sleep outcomes assessed with sleep diaries and actigraphy, further on insomnia (Bergen Insomnia Scale), sleepiness (Karolinska Sleepiness Scale) and arousal (Pre-Sleep Arousal Scale).

Paper 3 aimed to investigate the effect of blocking the blue light in the evening on the melatonin profile. The third paper assessed sleep by sleep diaries, and melatonin was measured based on saliva samples.

Results: Paper 1 reported an insomnia prevalence of 38% of the pregnant women, compared to 51% in the non-pregnant group. Sleep diary data showed lower sleep efficiency, and actigraphy data showed longer total sleep time and higher exposure to evening light in pregnant women, compared to the non-pregnant women. In the pregnant women, the stress variables were not associated with sleep outcomes, while light exposure in the evening was inversely associated with total sleep time and sleep efficiency measured by actigraphy.

Paper 2 found no effect of blue-blocking glasses on neither of the sleep outcomes total sleep time, midpoint of sleep, sleep efficiency and daytime functioning, nor on insomnia, sleepiness and arousal.

In Paper 3 we estimated the melatonin profile in 47 pregnant women (data for some participants were discarded as their values were out of range). This paper showed that blocking the blue light in the evening resulted in an earlier onset of melatonin in the evening, and higher melatonin levels at some evening time points. Following the intervention, the phase angle (time interval) increased between melatonin onset and bedtime and sleep onset time within the blue blocking group only. Still the difference between the two conditions in terms of phase angle changes were not significant.

Conclusion: The present thesis found that the participating healthy pregnant women in the third trimester slept quite well. Evening light exposure was associated with shorter sleep duration. Blocking blue light in the evening did not show statistically significant effects on sleep outcomes. However, by using BB-glasses in the evening we found a positive effect on the circadian system by preventing suppression of melatonin. Melatonin is a clinically important hormone for both mother and fetus. It is concluded that BB-glasses may be an effective and safe non-pharmacological chronobiological intervention during pregnancy, still more research is needed on this intervention.