Circadian Rhythms and Longevity: How Our Circadian Clock Dictates Healthspan and Lifespan
Our circadian rhythms are our body’s 24-hour internal clocks, which regulate everything from sleep timing to body temperature to hormone secretion. But what used to be relatively straightforward in the lives of our ancestors, who simply rose with the sun and slept with the moon, is now disrupted day in and day out by artificial light, constant access to food, rapid travel across time zones, shift work, and more.
While you may think that a disrupted circadian rhythm only impacts how well—or poorly—you sleep, that couldn’t be farther from the truth. Research over the past two decades has begun to uncover just how much an out-of-whack circadian rhythm can impact our health, ranging from metabolism and heart health to cognitive function and longevity.
Circadian Rhythms 101
Although we have Thomas Edison to thank for his ingenious invention of the light bulb, we must also acknowledge the detrimental effects of artificial light on our health. For thousands of years, humans had followed the sun and moon cycles—up until about 150 years ago, when electric lighting started to become commonplace, disrupting our finely-tuned, thousands-of-years-in-the-making circadian rhythms.
In humans, the most powerful circadian rhythm regulator is daylight. Seeing daylight stimulates receptors in the retinal ganglion cells—neurons in the inner surface of the eye’s retina. The retinal ganglion cells transmit visual signals (like seeing sunlight) into electrical signals that stimulate other neurons in an area of the brain’s hypothalamus called the SCN (suprachiasmatic nuclei). These visual-turned-electrical signals activate circadian clock proteins in the SCN, which is the central pacemaker of our circadian rhythm.
But the SCN doesn’t just control sleeping and waking—it also coordinates the timing of the billions of other circadian clocks found in cells all over our bodies that regulate metabolism, hormone secretion, digestion and gut motility, mitochondrial function, blood-brain-barrier permeability, and more. Although many genes and proteins are involved in these processes, two crucial genes, aptly named CLOCK and CYCLE, are known to regulate circadian rhythm activity.
How Does the Circadian Clock Change With Age?
Progressive declines in circadian rhythm function are a common hallmark of aging. If you used to sleep in until 9 A.M. easily but now find yourself waking with the roosters, this is a prime example of age-induced circadian changes. Research shows that older adults tend to go to sleep 1-2 hours earlier than younger adults, and they experience more frequent nighttime awakenings, take longer to fall asleep, and spend less time in REM sleep than 20-30-year-olds. Older adults also experience changes to body temperature fluctuations throughout the night and melatonin and cortisol release.
Many factors are potentially at play here, including changes in the size and structure of the SCN with age, changes in clock gene expression, or reduced synaptic activity in the brain. However, alterations to our internal clocks may not merely be a biomarker of aging, but rather, circadian rhythm dysfunction might play a causal role in aging.
Circadian Rhythms and Healthy Aging
In research with animals, those with disrupted circadian clocks develop many age-related conditions and symptoms. This suggests that correcting circadian rhythm imbalances may counteract some aspects of the aging process, including poor metabolic health, cognitive loss, and even lifespan itself.
Circadian Rhythms and Metabolic Health
Increased exposure to artificial light at night is known to disrupt circadian rhythms. This disruption is linked to undesirable metabolic changes, including increased body weight and waist circumference and higher triglyceride and unhealthy cholesterol levels in older adults.
Circadian rhythms impact metabolic health by altering glucose tolerance and insulin activity at various times throughout the day. At night, glucose responses are impaired due to reduced insulin secretion. This suggests that eating late at night and shift working (where you eat your lunch at midnight, for example) will be met with abnormal blood sugar metabolism, leading to a whole host of metabolic conditions.
One study placed healthy adults on an extended 28-hour “day” in a laboratory, shifting their normal sleep-wake cycle 12 hours forward. This shift led to increased blood glucose and blood pressure levels and elevated their post-meal glucose responses in the range typical of people in a prediabetic state.
Heart health has also had a long-established link to the circadian rhythm, as research has demonstrated that the incidence of cardiovascular events is three times greater in the morning than in the evening.
Circadian Rhythms and Brain Health
The health of our brains is also tied to the health and functionality of our circadian rhythms—which makes sense, as the SCN is composed of over 20,000 neurons. Our circadian clocks play a role in several aspects of brain health, including cognitive processing, memory, and mood. This is known intuitively by many of us—just imagine being woken up at 3 A.M. and trying to solve complicated math problems or remain in a good mood.
Circadian aging not only contributes to a decline in cognitive performance in older adults but may also be involved with the development of neurodegenerative conditions. Sleep disturbances have been found to be some of the earliest symptoms of these conditions, and circadian clock and sleep abnormalities tend to worsen as the conditions progress.
Circadian Rhythms and Longevity
In addition to regulating age-related conditions, the circadian clock is tied to several markers of longevity—and possibly lifespan itself.
Circadian rhythm disruptions from artificial lights, combined with eating erratically around the 24-hour cycle, lead to compromised longevity by promoting energy storage and not allowing adequate time for our bodies to “clean house” overnight, a process known as autophagy. Autophagy, which means “self-eating," refers to how our bodies recycle or remove damaged cells and toxic compounds to make room for new, functional cells. When autophagy is disrupted or reduced, the aging process accelerates, and diseases develop more rapidly.
The circadian clock has also been found to modulate the activity of SIRT1—a sirtuin protein dependent on the vital coenzyme NAD+ and linked to longevity. NAD+ itself may also be involved with circadian rhythms, as the rate-limiting enzyme for NAD+ synthesis called NAMPT has been found to decline in SCN neurons with age.
Further, in research with animals, mice without functional CLOCK gene activity—indicating dysfunctional circadian rhythms—had lifespans that were 15% shorter than “normal” mice.
How to Support Your Circadian Clock With Age
Although we can’t stop the aging process, there are several ways we can support our circadian rhythms as we grow older.
- Morning sunlight exposure. Getting daylight in your eyes first thing when you wake up can help to reset your circadian clock, which “tells” your body it’s daytime and will help you sleep better at night.
- Avoiding excessive artificial light at night. Conversely, artificial light at night tells your body to stay awake, delaying the normal nighttime metabolic and hormonal response. It’s especially important to avoid blue light (like from screens), as blue light is the same type found in morning light. Therefore, blue light exposure at night tells our bodies and brain that it’s daytime.
- Establish consistent sleep-wake times. Waking up and going to sleep within a one-hour window every day (yes, even on weekends) can help to support a healthy circadian rhythm.
- Intermittent fasting or caloric restriction. Dietary (or caloric) restriction—the reduction of total calories or nutrients consumed daily—is known to delay disease and extend lifespan. The mechanisms driving these benefits may be tightly linked with our inner clocks, as dietary restriction or intermittent fasting enhance autophagy and preserve circadian function with age.
- Avoid late-night eating. Eating or drinking in the 2-3 hour window before bed can delay your circadian rhythm, as we’re not designed to be digesting food when we sleep.
- Avoid evening caffeine and alcohol. Similarly, caffeine and alcohol in the later hours can delay your circadian clock functions.
- Supporting NAD+ levels. As NAD+ has been found to be involved with circadian rhythms and SCN neuron activity, maintaining its levels with age with NAD+ precursors like NMN or NR may be able to support your inner clock.
Circadian rhythms are an essential component of human health—but many aspects of modern society have disrupted its previously finely-tuned perfection. From artificial lights to midnight snacking to working late hours, dysregulated circadian clocks are now commonplace. But this doesn’t just impact sleep, as circadian rhythms play a role in cardiovascular and metabolic health, cognitive function, and even longevity.
Although sleep patterns are known to change as we grow older, there are many things you can do to support your circadian rhythm with age, including getting morning sunlight exposure, avoiding bright lights at night, boosting NAD+ levels, and more.
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