The time change can have effects on your body’s internal clock that last beyond the first night that you “spring forward.” You can think of your circadian rhythm as the internal schedule your body follows, which helps keep daily bodily functions (not just sleeping and waking, but things like metabolism, too) regularly happening at the right times. Your internal clock is accustomed to daylight and darkness consistently happening at certain times of the day. It can take time to adjust to changes, which is why jet lag happens.
“The body doesn’t do very well when it’s asked to live in a different time zone,” says Elizabeth B. Klerman, MD, PhD, a professor of neurology at Harvard Medical School and a sleep research investigator at Massachusetts General Hospital in Boston. Changing the clocks for DST has effects similar to jet lag, which we know can be damaging to health in the long term.
Cues from the sun generally keep these circadian rhythms on track (via a network of cells in the brain referred to as the “body clock”), Awad says. But our behaviors — sleeping in much later than usual on a Saturday, spending a lot of time in the evening in front of bright screens (which the body registers as stimulating sunlight), or eating a big meal in the middle of the night — can send mixed messages to the body and misalign the body’s various circadian rhythms.
Traveling across time zones and switching the clocks for DST have similar effects, misaligning your body’s clock to the one on the wall and the rotation of the sun, Awad explains. DST results in more hours of darkness in the morning, and more hours of daylight in the evening.
“Nighttime light and morning darkness shift your body to a later time, but the social clock has moved to an earlier time, so it’s harder to fall asleep, and people get less sleep,” Dr. Klerman says. “And we know that many bad things happen from not getting enough sleep,” she adds.
DST’s Body Clock Effects on Heart Health
Our bodies will, of course, adjust to the new schedule after a few days or a week, but there’s evidence that the change may still affect our health, particularly heart health.
The mechanisms behind this phenomenon are still up for debate, and research is ongoing. But it may be that DST disrupts the regular release of the stress hormone cortisol, which may make existing heart problems worse and increase the risk of heart problems in older adults, according to Jamie M. Zeitzer, PhD, a research professor at the Stanford Center for Sleep Sciences and Medicine in Palo Alto, California.
Normally, your cortisol levels rise around the same time every morning to give you the energy you need to ease out of sleep and into a wakeful state. “If you’re getting up too early, that cortisol spike hasn’t happened yet,” Dr. Zeitzer says. Without cortisol to help, your heart has to work a lot harder to get you moving again, increasing your risk of heart problems.