Bryndís Benediktsdóttir^1,2

Tinna Karen Árnadóttir³
Þórarinn Gíslason^1,2
Jordan Cunningham²

Björg Þorleifsdóttir¹

¹Faculty of Medicine, University of Iceland, ²Department of Sleep, Landspitali University Hospital Reykjavík, Iceland, ³Primary Care of the Capital Area.

Correspondence: Bryndís Benediktsdóttir, brynben@hi.is

Key words: sleep duration, sleep time, circadian rhythm, sleep and health, sleep of Icelanders.

 

Sleep health promotion is an ever-increasing subject of public discourse in Iceland. Prominent claims made include that the duration of sleep among Icelanders is shortening, and that changing sleeping habits constitute a significant public health risk. Like many aspects of healthcare, commercial interests and sales hype can skew perception. This review article will seek to shed light on the scientific background of these statements. International meta-analysis suggests there has been little change in sleep duration in adults over the past century. The duration of childrens sleep has shortened, but the consequences of this are not yet well established. Significant shortening of the sleep of adult Icelanders has not been demonstrated. No difference in sleep duration is found between Icelandic adults and adolescents and comparable groups in neighboring countries. The measurement methods that are used when comparing sleep studies are variable and can lead to different results. Associations have been established between sleep duration and adverse health outcomes, both physical and mental, but causality has not yet been established, and potential important mediators of the relationships are discussed.
The circadian sleep phase of Icelanders is generally delayed relative to neighbors, likely related to Iceland‘s diurnal length variation at sub-Arctic latitudes and longitudinal discrepancies between natural light and local time.

Figure 1: Sleep diary. Fill out every morning. Mark with a line your sleep periods the last 24 hours.

Figure 2. Mean sleep duration for each sleep measure and each time point in 225 adolescents.

 

Figure 3. Sleep duartion recommenations (National Sleep Foundation).

Figure 4. Circadian rythm.

Figure 5. Nonlinear dose‐response analyses of sleep duration and risk of all‐cause mortality (A), total CVD (B), CHD (C), and stroke (D). CHD indicates coronary heart disease; CVD, cardiovascular disease.