Influence of Nocturnal Light Exposure on the Impairment of Glucose Tolerance Induced by Chronic Sleep Restriction

Laboratory studies have shown that sleep restriction to 4-6h per night for durations varying from one to 14 days reduces glucose tolerance in otherwise healthy adults, but the mechanisms by which insufficient sleep impairs glucose metabolism are still unknown. Current theories are based on the premise that the adverse metabolic consequences are caused by reduction in the duration of sleep per se. However, sleep curtailment is typically accompanied by longer exposure to artificial light at night (ALAN), which is an environmental endocrine disrupter that profoundly disrupts circadian rhythms.

The investigators have previously reported that acute circadian misalignment induced hyperglycemia comparable to pre-diabetic states in a third of otherwise healthy participants. Since then, the investigators have shown that even when the circadian phase of participants was realigned, prior exposure to 2 ½ weeks of chronic sleep restriction combined with a history of recurrent circadian disruption induced even more deleterious effects on glucose metabolism, in which pancreatic beta cells failed to respond adequately to increased glucose levels. Moreover, both night and rotating shift work (which induce circadian disruption) are associated with increased risk for metabolic problems. Night shifts can lead to acute increases in glucose and insulin levels, although some studies report reduced insulin release in response to meals consumed during the night. Given that circadian disruption has been shown to independently adversely affect metabolism, and exposure to ALAN adversely impacts metabolism in animals, it is important to understand the extent to which circadian disruption contributes to the observed impact of sleep curtailment on metabolism. No previous studies of the metabolic impact of sleep restriction in humans have controlled for this additional exposure to ALAN, thus confounding the effects of sleep restriction with the effects of circadian disruption caused by extended exposure to ALAN.

Inclusion criteria

• Healthy adults with conventional and regular sleep-wake timing
• Non-smokers
• Completion of medical, psychological, and sleep screening tests
• Able to spend 33 consecutive days/nights in the laboratory
• Normal color vision

Exclusion criteria

• History of neurological or psychiatric disorder
• History of sleep disorder or regular use of sleep-promoting medication
• Current prescription, herbal, or over-the-counter medication use
• Traveling across 2 or more time zones within past 3 months
• Donating blood within past 8 weeks
• Worked night or rotating shift work within past 3 years
• Hearing impairment, visual impairment
• History of eye trauma or surgery
• Drug or alcohol dependency