By Carolyn Crist
(Reuters Health) - Adults who have a regular bedtime are likely to weigh less than those who don't, to have lower blood sugar and to face a lower risk of heart disease and diabetes, according to a U.S. study.
Although scientists have talked about the importance of getting enough sleep and getting quality sleep, it matters how regular your sleep schedule is as well, the researchers write in Scientific Reports.
"Irregular sleep patterns are common in people of all ages," said lead author Jessica Lunsford-Avery of Duke University Medical Center in Durham, North Carolina.
"Among older adults who have left the workforce, however, that problem may be exacerbated," she said in a phone interview.
Sleep regularity, also called sleep hygiene, is optimal when someone goes to sleep at the same time each night and wakes up at the same time each morning, including on weekends. This helps the body's circadian rhythm to stay on track and regulate other body functions such as appetite and digestion.
Lunsford-Avery and colleagues analyzed the sleep cycles of nearly 2,000 adults with an average age of 69 years by using a new metric called the Sleep Regularity Index. The index looks at sleep variation across a 24-hour day and compares one day to the next to understand regular sleep and wake times as well as midday naps.
They used data from participants in a large, long-term study who wore actigraphy wrist devices to record sleep/wake measurements, physical activity and light exposure. The participants also completed sleep diaries and recorded their daytime sleepiness. Researchers used other data to measure their cardiovascular risk factors and psychiatric health.
People with high sleep irregularity tended to go to bed later, to sleep more during the day and less at night than regular sleepers, to have reduced light exposure and higher daytime sleepiness, researchers found.
Greater sleep irregularity was also associated with a higher 10-year risk of heart disease as well as greater obesity, hypertension, fasting glucose and diabetes.
Sleep irregularity was also tied to greater stress and depression, which are linked to heart disease risk as well. Importantly, African Americans were most likely to have the greatest sleep irregularity, the study authors note.
"Among the three types of sleep problems - duration, regularity and timing as a morning lark or night owl - sleep regularity was the most consistently and strongly associated with health," Lunsford-Avery said. "That underscores the importance of it."
Future studies should look at the mechanisms that connect sleep irregularity and disease risks, as well as the cause-and-effect relationships, Lunsford-Avery said. In this ongoing long-term study, she and her colleagues will continue to evaluate disease risk factors as they follow the participants over time.
"When we think about sleep and health, we think about duration or quality, but not until recently did people look at the regularity," said Andrew McHill of the Oregon Institute of Occupational Health Sciences in Portland, who wasn't involved in the study.
In particular, people with shift work jobs or late-night social activities may be disrupting their natural circadian cycles, which in turn encourages them to eat more calories and reduces their sugar metabolism, he noted.
"Keep a regular schedule as much as possible," McHill said in a phone interview. "It's understandable that every now and then it's not possible, but you've got to be cognizant of it and get yourself back on track."
Body-clock misalignment can lead to irregular sleep, irregular eating and increases in blood pressure, hypertension and diabetes, said Frank Scheer, director of the Medical Chronobiology Program at Brigham and Women's Hospital in Boston, who wasn't involved in the current study.
"The exciting findings include the question, 'What can we do about it?'" Scheer told Reuters Health by phone.
"In the broader sense, a regularity in bedtime and wake time is key," he said. "Fundamental mechanisms are at play, so if we can think about ways to get the best sleep and keep a regular bedtime, it may be one of the most important pieces of advice for good sleep hygiene."
SOURCE: go.nature.com/2xIfT5O Scientific Reports, online September 21, 2018.