Keynote speaker: ‘Sleep, circadian rhythm are inseparable’

INDANAPOLIS — Circadian disorder is the flagship of sleep-wake disorders, Phyllis C. Zee, MD, PhD, said in her keynote address at the SLEEP meeting.

In her lecture about bridging circadian and sleep science to enhance health span, Zee, director of the Center for Circadian and Sleep Medicine at Northwestern University Feinberg School of Medicine in Chicago, said, “Sleep and circadian rhythm are inseparable.

“Clinicians think of circadian disruption as a disorder of the sleep-wake cycle,” she said. “Circadian biologists are looking at so many additional elements. Even though circadian disorder is the flagship of sleep-wake disorders, the wall clock does not equal your biological internal clock, yet we assume that it does in our clinical practice.”

Zee discussed the “power of light,” which combines sleep and circadian rhythm. Both natural and artificial light affect physical and mental health outcomes, including immune, cardiometabolic and cognitive function as well as mood and sleep quality, she said. Natural light during the day has beneficial effects, while artificial light at night has disadvantages.

Research has shown that sleep quality improved, and physical and motor activity was higher during the day in patients with Parkinson’s disease who were exposed to daytime bright light for 2 weeks. This led to NIH supporting ENLITE PD, a trial investigating the use of light therapy to treat PD-related sleep disturbances, Zee said.

“We need more of this type of work to show that sleep and circadian interventions can be scalable to the population,” she said. “It’s not only how much, but it is when. Timing is very important.

“Sleeping with our lights on messes with our systems,” she continued. “We’re sleeping late, eating late. Sleep could be the one modifiable factor that affects our biology widely, but also has social implications. People in lower socioeconomic classes tend to live in large cities where there’s light from streetlamps.”

Other research has shown that light at night in older age is associated with obesity, diabetes and hypertension.

“It’s pretty significant and begs the question whether they’re due to each other,” Zee said.

Ongoing research from Minjee Kim, MD, also from Northwestern, shows that exposure to light at night increases the odds of diabetes in pregnancy (Paul M.), she said.

“There’s no difference in gestational diabetes in regard to activity level, but there’s a difference in light exposure 3 hours before bedtime,” Zee said. “The odds ratio is fairly high where if you are exposed to light 3 hours before bedtime you are at higher risk for gestational diabetes.”

Recent research from Mason and colleagues showed that just one night of light exposure during nighttime sleep impairs cardiometabolic function, she said.

“It has a significant effect on glucose; [study subjects] had to secrete a lot more insulin to maintain glucose level,” Zee said. “Unexpected to me, the heart rate was higher at night.

“Sleep and circadian disturbance have broad implications for disease expression and treatment.”

She discussed research involving critical ailments in the ICU by Maas and colleagues (LaBuzetta JN, et al.).

“We always thought there was too much light in the ICU all the time,” Zee said. “But when you measure it, it was not too much light only at night; it was not enough light during the day.

“They concluded that circadian rhythm disruption during critical illness is not limited to the brain, not only to sleep, but also the circadian system,” she said. “Changing this milieu perhaps can decrease mortality and improve outcomes. This is a great opportunity as we look to the future.”

References:

• LaBuzetta JN, et al. Curr Treat Options Neurol. 2022;doi:org/10.1007/s11940-022-00724-5.
• Mason IC, et al. Proc Natl Acad Sci. 2022;doi:org/10.1073/pnas.2113290119.
• Dim lights before bedtime to reduce risk of gestational diabetes. https://news.northwestern.edu/stories/2023/03/new-story-pagedim-lights-before-bedtime-to-reduce-risk-of-gestational-diabetes/. Published March 13, 2023. Accessed June 5, 2023.