Sleep expert says daylight saving time comes at a cost to your health

Americans set their clocks ahead one hour on Sunday to transition into daylight saving time. That "springing ahead," however, can come with serious negative health effects—including an increase in total heart attacks and teen sleep deprivation—researchers discovered.

Beth Ann Malow, director of Vanderbilt University Medical Center's sleep division and a professor of neurology and pediatrics, has spent more than five years studying the health effects of daylight saving time. The results are concerning.

"It's become clear to me and many of my colleagues that the transition to daylight saving time each spring affects health immediately after the clock change and also for the nearly eight months that Americans remain on daylight saving time," she reported to The Conversation in 2022.

Standard time, when the sun is directly overhead around noon, approximates natural light more closely than daylight saving time, when natural light is present an hour later in the morning and evening. It's that hour less of natural morning light that affects our health.

"Morning light is essential for helping to set the body's natural rhythms: It wakes us up and improves alertness," Malow said. "Morning light also boosts mood—light boxes simulating natural light are prescribed for morning use to treat seasonal affective disorder.

"Although the exact reasons why light activates us and benefits our mood are not yet known," she continued, "this may be due to light's effects on increasing levels of cortisol, a hormone that modulates the stress response, or the effect of light on the amygdala, a part of the brain involved in emotions."

The extended light exposure during the evenings causes issues as well, including interfering with sleep by delaying the brain's release of melatonin.