Before heading to bed on Saturday, November 2, many Americans will set their clocks back one hour to prepare for the end of daylight saving time (DST). In the states that change clocks (Arizona and Hawaii are the only ones that do not), this “fall back” time is always the first Sunday in November.[1] This year, DST officially ends at 2 a.m. on Sunday, November 3, 2024, after an eight month run that began March 10. If you find yourself rejoicing each year over the extra hour of sleep, we hear you. But some medical experts say the extra slumber may have some unintended consequences for our health.

Here’s what you should know about the science behind why this time change may not be so great for health, and some tips for easing the transition.

Changing the Clocks on the Walls Can Throw Off Our Body Clocks Setting the clock back affects your body’s circadian rhythms — “the physical, mental, and behavioral changes in your body that follow a 24-hour cycle,” according to the National Institute of General Medical Sciences (NIGMS) definition.[2] Our bodies expect certain things to happen at certain times during the day (like sleeping, waking up, and eating) based on cues from the sun and on your doing those things over and over again at the same time every day. For example, says Aneesa Das, MD, a sleep medicine, internal medicine, and pulmonary disease specialist at The Ohio State University Wexner Medical Center in Columbus. “Natural sunlight during the day and the absence of light in the evening help to drive our circadian sleep phase.”

When you shift that routine — even by an hour — your circadian rhythms get slightly thrown off, similar to the effect of jet lag. The result: Your circadian rhythms become slightly misaligned from the time on the clock, which can throw off the timing of several daily processes that happen in the body, like sleep, digestion, and cardiovascular functioning.[3] And while many people may not feel all that affected by the change, large-scale data suggests that the risk of health problems like heart attacks and accidents may increase because of the change to and from DST.

One study that followed healthcare workers for eight years revealed an 18 percent uptick in safety-related human errors in the week following DST in the spring and a 5 percent increase after the end of DST in the fall.[4] Any disruption in the sleep or circadian cycle has the potential to increase risk of disease, says Matthew Morgan, MD, a primary care physician at Ochsner Health Center in Chalmette, Louisiana. Changes in daylight patterns — like the shorter days during fall and winter months — also affect your body’s normal sleep-wake cycle.

But those changes happen gradually over the fall months as the days get shorter (particularly in places farther north). DST clock changes happen overnight. “It can take several weeks for your circadian rhythm to adjust to the change that the end of DST brings,” adds Whitney Hardy, MD, a family medicine physician at Ochsner Health Center in Gretna, Louisiana.