The study wasn’t designed to say whether sleep is the chicken, the egg, or both when it comes to mood. “It could definitely be the case that the women in our study who had depressive symptoms had a different type of sleep schedule because they were depressed, or that their depression was causing them to have more irregular sleep-wake patterns,” said study co-author Leslie Swanson. She is an associate professor of psychiatry at the University of Michigan, in Ann Arbor.
More research is needed to tease out the cause and effect between sleep and mood, particularly in postmenopausal women, Swanson said. “Women might be more prone to more irregular sleep patterns as they get older due to factors such as retirement from work or aging of the parts of the brain that control the timing of sleep,” she suggested.
“Even small changes in the timing of sleep, such as those caused by daylight saving time changes, can disrupt our circadian rhythms, which can, in turn, negatively impact factors that cause depression, anxiety and lower well-being,” Swanson said. Our circadian rhythm is the 24-hour internal clock that controls the release of the hormone melatonin to encourage sleep.
For the study, the researchers analyzed sleep patterns and assessed the psychological health of close to 1,200 postmenopausal women aged 65, on average.
Women with a sleep midpoint — the halfway point in clock time between falling asleep and waking up — that fell outside 2 and 4 a.m. were 72% more likely to report significant depression symptoms. Sleep midpoints determine if you are a morning lark or a night owl. If your sleep midpoint is 3:30 a.m. or earlier, you're probably a lark, and if it is 5:30 a.m. or later, you're likely an owl.
Each hour of sleep schedule irregularity increased in a woman’s chances of experiencing significant depressive symptoms by 68% and significant anxiety symptoms by 62%, the study authors noted.
Sleep was more irregular among Black women than among white, Chinese and Japanese women, the researchers found.
Getting regular, high-quality sleep is essential for physical and mental health, Swanson said.
Set an alarm clock for the same time every morning, seven days a week, even after retirement to make sure you wake at the same time every day and get into bright light as soon as you can after your alarm goes off, she advised.
Exposure to bright light sends a strong signal to your circadian clock about when you want to be awake and asleep, Swanson explained.