The notion that our circadian clock is simply about sleep is unfortunate. So is advice that puts our sleep habits on trial when our sleep–wake rhythm is woefully out of whack.

At least two daily habits that seemingly have nothing to do with sleep appear to reset the circadian clock—sometimes quite rapidly. Not surprisingly, the habits themselves revolve around timing: when to view light and when to eat.

In a physiological sense, we human beings are made from the air we breathe, the food we eat, and the sunlight that triggers biochemical processes in our bodies. This same sunlight feeds the plants we eat, which also feed the animals we eat. Plants are biochemically solar-powered, converting sunlight into food and growth. All that to say, the sun is far more than a universal alarm clock, it has a biochemical effect on our bodies and everything we eat.

Most people can fix those issues quickly with the insights detailed below. But there are three groups that almost universally deal with circadian disruption that may be harder to fix: shift workers, teenagers, and people in their 60s who often suffer from daytime sleepiness and night disruption when their internal clock changes later in life. While we know that quality sleep is essential for overall health, it can sometimes feel very difficult to control, making it challenging to treat sleep issues—especially without medication.

The discovery of this gene prompted a Nobel Prize in 2017 for the researchers who found it. They discovered that it produces a protein that builds up in cells overnight and then breaks down during the day. This mechanism has a significant influence on sleep, cognitive function, and more. It doesn’t just work at a cellular level though. Just as our cells make up larger tissues, including organs and cellular-based activities such as inflammation, so, too does this gene influence larger processes and systems.

There is also a master clock in the brain—about 20,000 neurons that form the suprachiasmatic nucleus (SCN)—that works to keep all the clocks synched at the right time. Much like a car needs a crankshaft to move engine pistons in perfect timing, the SCN requires light to coordinate all these complicated tasks. The input of light relies on our eyes, but it’s independent of our sight. All it needs is the retina—a bridge between light and the SCN.

“There are studies out there that have shown that just two nights of not getting enough sleep can start to almost make people look prediabetic,” Broussard said. “In those studies, we took healthy young people and did that. The studies haven’t been done in older adults mostly because there’s this concern you might push people over the edge and elicit too strong a response.”

Researchers want to know if certain behaviors can be leveraged to overcome the health deficits of living misaligned with the Earth’s clock or whether lifestyle choices could improve the afternoon lag common in seniors that sends them to bed early and wakes them prematurely.

This is why late-night snacking is particularly vexing. Eating tells the body there is work to do. So does light.

“There’s a circadian rhythm to almost all physiological processes,” Broussard said. “When the light comes up ... the body’s parts are anticipating you’ll be active and eating, so systems are ready to go.”

Ideally, breakfast should be eaten within an hour of waking, and all eating should cease eight to 12 hours later. This is based on mice and human research, she said.

“Most of the research suggests the earlier side is when your body is expecting food intake,” Broussard said.

When you stop eating and let the belly empty itself, you send a powerful signal to the body that it’s time to sleep. When the body isn’t digesting food, it moves into repair and regeneration mode, an entirely different set of cellular processes that amount to cleaning up the factory after all the workers have gone home for the day. We now call this habit of intentionally limiting our eating to certain times “intermittent fasting” or “time-restricted eating.”

This habit also cuts down on insulin production, which improves glucose metabolism and insulin reaction.

Researchers found that circadian rhythm quickly adjusted to daylight—when people were actually exposed to it.

Researchers found that the campers quickly achieved an earlier circadian rhythm, preventing the typical weekend circadian sleep delay, which contributes to social jet lag on Monday mornings. Social jet lag is the mismatch between biological and social timing. Basically, your body hasn’t fired up enough to deal with the day’s work and social activities. Campers received four times the bright light exposure compared to what they would get in a typical home and work environment.

We can’t all live in tents, but Park said that a simple bright light (10,000 lux) can be used to train the body to get back on track after circadian disruptions. To do so, take note of when you notice a trend in tiredness, say at 6 p.m. every day. Sit in front of the light—not necessarily looking directly at it—for 15 to 20 minutes about an hour before then (at about 5 p.m.) to help extend bedtime to a more normal hour.

Using this as a daily habit, along with morning light exposure, can shift the sleep-wake cycle later for those older adults who feel exhausted by 8 p.m. but then end up waking at 3 or 4 a.m. They would use the artificial light at 7 p.m. to give them a boost and hopefully keep them awake for longer.

“Sunlight itself has a beneficial effect on your circadian rhythm every morning, but another thing it benefits is vitamin D. Most people don’t have enough vitamin D,” Park said.

You can likely tune into this yourself by simply tracking when you start to feel really tired each night. This knowledge can offer helpful insight for those suffering from related disorders so that they can enhance their natural rhythm and figure out the best timing for medication, meals, and light exposure.

And sometimes, simply forcing yourself to “go to bed earlier” to fit into an idealized circadian rhythm is actually bad advice, Broussard said. Instead, she advocates creating the sleep schedule that works best for your life or rearranging your life around your ideal sleep schedule.

“Everybody knows what their preferred sleep schedule is. Let go of the guilt of sleeping in,” she said. “Most people are of a later chronotype ... There’s this judgment that you’re lazy if you sleep in and you’re morally superior if you wake up earlier.”

Part of precision medicine is to give people permission and agency to do what’s best, Broussard said. That might mean letting go of the notion that only the early bird gets the worm.