Sleep architecture is related to the season of PSG recording in 8-month-old infants

ABSTRACT

To date, little is known about the impact of season on infant sleep. In higher latitudes, the duration of daily light time varies substantially between different seasons, and environmental light is one potential factor affecting sleep. In this cohort study, one-night polysomnography (PSG) was performed on 72 healthy 8-month-old infants in 2012 and 2013 to study the effect of season on the sleep architecture of young infants in Finland. The children were divided into four subgroups, according to the amount of light during their birth season and the amount of light during the season of the PSG recordings, corresponding to spring, summer, autumn, and winter. We found that the season of birth did not have an impact on the infants’ sleep architecture at 8 months of age, but the season of the PSG recording did have an effect on several sleep variables. In the PSGs conducted during the spring, there was less N3 sleep and more N2 sleep than in the PSGs conducted during the autumn. In addition, there was more fragmented sleep during spring than autumn. According to our data, the season has an effect on the sleep architecture of young infants and should, therefore, be considered when evaluating the PSG findings of young infants. The exact mechanisms behind this novel finding remain unclear, however. The findings imply that infants` sleep is affected by the season or light environment, as is the case in adult sleep. Since potential explanatory factors, such as direct natural or artificial light exposure and the melatonin levels of the infants, were not controlled, more research is needed in the future to better understand this phenomenon.

KEYWORDS:

• Infant sleep
• polysomnography
• season
• chronobiology
• seasonality
• environmental light
• SWS
• N3 sleep

Acknowledgements

We thank Tytti Koskelo, who organized and performed the PSG recordings.

Disclosure of interest

The authors report no conflict of interest.

Additional information

Funding

This study was funded by Academy of Finland, Grant no. 134880 and 308588, by the Competitive Research Financing of the Expert Responsibility area of Tampere University Hospital, Grant nos. 9R007, 9R004, 9S007, 9S058, and 9P013, by Tampere University Hospital Support Foundation, Tampere University Hospital (Grant no MK243), and by Tampere Tuberculosis Foundation (Grant no MS860). AS has received grants from the Finnish Sleep Research Society and The Research Foundation of Pulmonary Diseases; The Research Foundation of Pulmonary Diseases (HES); Finnish Sleep Research Society (SUS); Tampereen Tuberkuloosisäätiö [MS860].