How to Unlock Better Sleep Using Sunlight and Diet
Your diet and the sun cooperate to influence your sleep quality at night.
Updated May 27, 2026 | Reviewed by Ekua Hagan
We evolved on a planet that spins in front of a fairly bright star. Consequently, we humans, as well as all other organisms, developed a circadian rhythm in our physiology and behaviors with the following rules: Wake up when the sun shines and eat, and when it gets dark, rest your brain and body and sleep for about seven hours.
If you decide not to follow this rule, there are dire consequences. A recent study demonstrated that sleeping for less than six hours—or more than eight—significantly accelerates the aging process of every organ in your body. Getting too little sleep leads to impaired immune function, obesity, increased joint inflammation, a higher incidence of metabolic syndrome with insulin insensitivity, diabetes, cancer, and cognitive impairments.
Unfortunately, getting a good night’s sleep is a challenge for most adults. Studies indicate that our sleep is best during puberty ; our sleep quality begins to decrease in our late teens and continues to worsen slowly. Consequently, if you are over 40, you probably do not sleep well.
People from every culture around the world complain of insomnia . This explains why the market for sleep aids is worth more than $100 billion annually. Unfortunately, most of the sleep aids are either not effective or, with regard to drugs, develop tolerance with continued use.
Our bodies contain different biological clocks that ensure that physiological systems are primed to do the right things at the right times, such as the response of our immune system, the digestion and utilization of nutrients in the diet , and going to sleep at night. All of these clocks tick along to different rhythms that need to be synchronized every day with one critical signal—sunlight. As the terminator line that separates the daylit side from the darkness moves across the Earth’s surface, the biorhythms of all living organisms are reset and recalibrated. Our bodies are similar to a symphony orchestra waiting for the conductor (the sun) to wave his wand (sunlight) and signal all the various musicians to begin playing in harmony.
If only modern lifestyles could accommodate this critical recalibration. We spend too much time indoors. We eat too much too late in the day. Science has now clearly shown that correcting these two behaviors will greatly improve sleep and overall health.
The Effect of Light on Your Circadian Clock
Light is the most powerful signal for resetting and synchronizing your circadian clocks. Blue wavelengths are especially powerful. There’s an evolutionary reason for this. The first single-celled organisms that evolved in the oceans experienced blue light from the sky because it penetrates seawater more than other wavelengths. Their evolving nervous systems took notice of this wavelength of light. Later, land-dwellers evolved outdoors, also under the sky. Thus, our retinas contain light-sensitive cells that are not involved with seeing; their job is to inform our brain’s circadian pacemaker that the sun has risen.
Our circadian pacemaker requires bright light to operate properly. Unfortunately, today’s typical household lighting provides only about 100–250 lux, which seems adequate, but it’s not. Step outside, and even on an overcast day, you will experience about 10,000 lux of daylight rich with blue wavelengths. That level of illumination is what our circadian system evolved to require for resetting.
Bright blue light first thing in the morning synchronizes all the body’s circadian clocks, enhances alertness and cognitive performance during the day, and regulates the nightly surge of melatonin that tells the brain that it’s time to sleep. This is why the same blue light at night, from artificial lights and glowing screens, confuses the circadian system, suppresses the melatonin surge, and makes it harder to sleep. The worst time to expose the retina’s light detectors to blue light is near the midpoint of sleeping, around 3 a.m. At this time of the sleep cycle, even a dim hallway light bulb can impair sleep.
Overall, what matters most is contrast: Lots of bright light during the day and a consistently dark night. This schedule is vital to survival. Studies have shown that getting too little light during the day and too much night light can shorten your life expectancy by up to five years.
Our brains look for the blue light every day. Unfortunately, indoor lighting tends to emphasize green wavelengths, which are great for general vision but fail to influence the circadian system. I purchased energy-efficient window glass for our house and specifically got lenses for my eyeglasses that reduce blue wavelengths. Unfortunately, both decisions reduced the number of circadian-stimulating photons that reach my eyes. Aging compounds the problem; the lenses of the eyes become more yellow over time and filter out more blue light.
How Eating Habits Influence Circadian Rhythms
Everything related to food digestion has rhythms: The ability of the liver to metabolize food (and drugs) varies across the day. The release of hormones such as GLP-1 (everyone’s heard of this one) and insulin varies across the biorhythm.
Our bodies did not evolve to handle food all day long; they prefer to handle the bulk of our daily calories at the beginning and middle of our daily biorhythm. Eating lots of calories later in the day disrupts our biological clocks and leaves key steps of digestion incomplete. Our gut microbiome also dislikes receiving food late at night; its displeasure can lead to insomnia. Late meals elevate blood glucose levels and uncouple our liver and kidney clocks from the master clock located in the brain.
Also, diets high in sugar and saturated fat, such as sodas, pizza, and chips, induce the brain to spend more time in lighter sleep stages with more nighttime awakenings. Alcohol makes us feel drowsy but produces mainly light sleep and morning nightmares. In contrast, eating lots of fruits and vegetables during the day leads to better sleep patterns at night.
Spend more time outdoors or sit near windows. Get lots of bright light at the front end of your daily biorhythm. Turn down the brightness of lamps in the evening and turn off television and phone screens a few hours before going to bed. Consider reading a book near lights that produce less blue light. And, stop eating so much at dinner. Eat breakfast like a king, lunch like a prince, and dinner like a pauper—with no snacking before bed.
Peeples, L (2025) How to get the best night’s sleep: what the science says. Nature 646, 26-28, doi: https://doi.org/10.1038/d41586-025-03148-8
Windred DP, et al., (2024) Sleep regularity is a stronger predictor of mortality risk than sleep duration: A prospective cohort study. Sleep, Volume 47, Issue 1, https://doi.org/10.1093/sleep/zsad253
Mason IC, et al., (2022) Light exposure during sleep impairs cardiometabolic function. PNAS, 119 (12) e2113290119, https://doi.org/10.1073/pnas.2113290119
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Gary L. Wenk, Ph.D. , is a professor of psychology, neuroscience, molecular virology, immunology and medical genetics at the Ohio State University.
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