Mind Your Clocks
We evolved to have internal clocks that help our bodies do things at the most advantageous times. Early mammals were nocturnal because it was safer to be active when cold-blooded dinosaurs slept. The suprachiasmatic nucleus (SCN) is the master timekeeper located in our brain, while peripheral clocks are present throughout our bodies. These clocks help the liver prepare us to digest food, skeletal muscles to ramp up when we are active, melatonin to be released at dusk to help us sleep, kidneys to slow urine production at night, and cortisol levels to rise in the morning to increase alertness. When our circadian rhythms are out of sync, these biological systems don’t work as they should, negatively impacting our mental and physical health.
Light is the most important time cue for our internal clocks. In addition to rods and cones, our eyes have a third set of photoreceptors, ipRGCs, which detect the quality and quantity of light. These photoreceptors use blue light to determine the time of day. Exposure to a lot of light throughout the day, especially in the morning, improves alertness, performance, mood, and sleep quality.
However, exposure to blue light at night disrupts our clocks, preventing our bodies from preparing us for sleep. Artificial light at night is associated with depression, obesity, poor blood sugar control, and gut issues. Studies have also linked higher rates of prostate, breast, and thyroid cancers to greater blue light exposure at night.
The second most important time cue for our internal clocks is when we eat. Consistently eating within the same timeframe each day helps keep our clocks synchronized. Eating at different times, especially late at night, can cause internal clocks to become misaligned with the master clock. This can disrupt the release of the hunger hormone ghrelin and enzymes needed for digestion.
Many other factors can wreak havoc on our circadian rhythms, including shift work, early school and work start times, jet lag, and daylight saving time. Moving our clocks forward in the spring and back in the fall is detrimental to our health. While many people favor adopting daylight saving time year-round, staying on standard time would be more beneficial. Our bodies never fully adjust to daylight saving time because we lose a crucial hour of morning sunlight and gain an hour of evening light that derails our clocks. I enjoy having more daylight in the afternoon, but it’s the longer days of summer that I really appreciate. Year-round daylight saving time would keep us in the dark longer on cold winter mornings, negatively impacting our circadian rhythms and overall health.
Fortunately, innovators are working to develop tunable lights and glasses that provide bright blue light during the day and block it at night. These lights are already being tried out in hospitals, schools, nursing homes, and offices. Athletes are using these glasses and other circadian practices to combat jet lag, align their peak performance times with scheduled events, and maximize their energy prior to competing.
Until these options become more widely available, here are some things you can do:
- Spend as much time outdoors during the day as possible, especially in the morning, and skip the sunglasses some of the time. When indoors, stay close to a window. Abundant daylight can buffer the effects of nighttime light exposure.
- Limit screen use or dim your screen in the evenings, consider blue-light-blocking glasses, listen to audiobooks in bed, use an amber-hued nightlight in your bathroom, wear an eye mask while sleeping, and install blackout shades if there are bright lights outside your window. The more distinction between day and night light exposure the better.
- Eat in a consistent 10- to 12-hour window, preferably earlier in the day. Stop the late-night snacking!
- Learn more about circadian rhythms by reading The Inner Clock.