Fall is here—a time for sweaters and scarves, warm beverages and changing leaves. Nights grow longer as the sun sets earlier, and in many parts of the U.S., we “fall back” from daylight saving to standard time to accommodate this shift. We may celebrate the feeling of getting to sleep in, or we may mourn getting out of work for the day only to find that it is already dark. Feelings aside, you may wonder how this change affects our health and physiology.

Light, time and the circadian rhythm

Our circadian rhythms, or “body clocks,” are physiological patterns that occur over a day, the most notable of these being sleep and wake patterns. A structure in the brain called the suprachiasmatic nucleus produces melatonin in response to light and dark exposure. Melatonin is a hormone that affects how awake or drowsy we feel. Sleep is important for our wellbeing, and therefore, so is our exposure to light.

Little Shift, Big Consequences?

Our bodies’ rhythms are not quite 24 hours. In fact, without prompts from the sun or our watches, our internal clocks would run for about 24 hours plus 12 minutes each day. Mother Nature has a solution: Early morning light speeds up our body clocks, keeping us on track. Unfortunately, the opposite is true: nighttime light delays our rhythms, pushing us out of sync. 

In theory, standard time aligns more closely with our biological need for morning light, while daylight saving time worsens our mismatch with the 24-hour day. This misalignment has serious health implications: Daylight saving time is associated with cardiovascular disease, injuries, mental health disorders and other negative effects. One study suggests that yearlong standard time in the U.S. would prevent 300,000 strokes and 2.6 million cases of obesity.

The American Academy of Sleep Medicine, National Sleep Foundation and American Medical Association endorse year-round standard time.

Doing Our Part

Sunlight is the driver of the circadian rhythm, yet most of us now spend the majority of our days indoors. We’re surrounded by screens, which are linked to poor sleep patterns, likely because they simulate sunlight and can be used at any time. While we can hope for permanent standard time, as individuals, we can protect our health by minimizing late night screens and maximizing morning sun.