Late snacking, night-time artificial light exposure can mess up sleep for pregnant women

It is quite common for women to experience some type of sleep problem during pregnancy, and a recent study from Singapore identifies nocturnal eating and exposure to artificial light at night as factors that prevent pregnant women from sleeping soundly.

In a cohort of 299 expectant mothers at 18–24 weeks of gestation, nearly 40 percent reported poor sleep quality. Most of these women also reported taking their meals after 20:00 (56.4 percent vs 33.5 percent; p<0.001) and being exposed to artificial light ≥5 lux between 02:00–04:00 (21.4 percent vs 6.0 percent; p<0.001). [Nutrients 2022;14:2348]

Regression analyses confirmed that women with a nocturnal eating pattern were 1.5 times as likely as those who took their meals earlier to have poor sleep quality (risk ratio [RR], 1.51, 95 percent confidence interval [CI], 1.12–2.04). Likewise, women with night-time artificial light exposure had 1.6-fold higher likelihood of sleeping poorly (RR, 1.63, 95 percent CI, 1.24–2.13).

Both nocturnal eating (β 0.68) and light exposure (β 1.99) were associated higher Pittsburgh Sleep Quality Index score (≥5 indicative of poor sleep quality). Meanwhile, nocturnal physical activity and screen viewing before bedtime did not influence sleep quality.

The cohort was recruited from KK Women's and Children's Hospital, Singapore. Most of the women were of Chinese ethnicity (81.9 percent), followed by Malay (16.1 percent), Indian (1.7 percent), and others (0.3 percent). The 117 women who reported sleeping poorly had an overall mean global PSQI score of 5.43. Women with poor sleep were more likely to be non-Chinese, exhibit negative emotion, and have higher prepregnancy body mass index.

How to sleep better

“In pregnant women, nocturnal eating is common as they have physiological demands to meet an increased appetite,” according to researchers led by Dr See Ling Loy of KK Women's and Children's Hospital. [J Nutr Educ Behav 2019;51:598-607]

“Nocturnal eating of carbohydrate-rich foods, in particular, has paradoxical effects on sleep. On the one hand, it can decrease sleep latency due to the elevation of tryptophan and the suppression of orexin. However, it also results in poorer sleep quality, as the circadian rhythm of core body temperature is delayed and nocturnal melatonin secretion is reduced,” Loy explained. [J Nurs Res 2013;35:497-513; Neuron 2011;72:616-629; J Clin Sleep Med 2016;12:19-24; J Occup Health 2014;56:359-368]

To address the physical needs of pregnant women without compromising their sleep quality, Loy suggested eating a small amount of food that is low in calories and rich in protein, serotonin and folate, such as kiwifruit, or foods that contain melatonin, such as eggs, fish, nuts, and mushrooms. [Nutrients 2015;7:2648-2662; Asia Pac J Clin Nutr 2011:20:169-174; Nutrients 2017;9:367]

Meanwhile, exposure to bright artificial light in the evening can have ill effects on the biological circadian rhythm due to a reduction in melatonin production, which is responsible for the regulation of the sleep–wake cycle. Melatonin in pregnancy is essential for the optimal functioning of the placenta and foetus, and reduced levels may lead to pregnancy complications, including pre-eclampsia and neurological disabilities in neonates. [J Pineal Res 2012;53:417-425; Fertil Steril 2014:102:321-328; Reprod Toxicol 2008;25:291-303]

“Therefore, reducing exposure to artificial light at night might help improve sleep quality in the pregnant population and lead to optimal levels of melatonin, which is crucial for improved maternal and foetal outcomes. It is recommended that the sleep environment be as dark as possible, with a maximum average illuminance value of 1 lux,” Loy said. [PLoS Biol 2022;20:e3001571]

Nevertheless, Loy acknowledged that they could not exclude the possibility of reverse causality, where poor sleep might contribute to nocturnal eating and artificial light exposure at night. She called for well-controlled studies to ascertain this cause–effect relationship, examine the amount and breakdown of the type of food eaten and its association with sleep quality, and explore the reasons that lead pregnant women to engage in late-night snacking.