Your Body Clock May Contribute to Health Problems

When your body’s internal “clock” is out of whack, it can increase your risk of heart disease, diabetes, metabolic syndrome, obesity, and depression.

Although you aren’t consciously aware of it, your body has a built-in master clock in your brain, composed of about 20,000 nerve cells. It controls several other biological clocks, found in almost every tissue and organ in your body, which help maintain your health or, if they are out of sync, increase your risk of disease.

The biological clocks oversee various circadian rhythms, or physical, mental, and behavioral changes that roughly follow a 24-hour cycle. You take these cycles — connected primarily to light and dark — for granted when daily habits are normal. When disrupted, however, they can wreak havoc.

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Circadian rhythms help determine human sleep patterns by triggering the master clock to produce melatonin, a hormone that makes you sleepy. It’s no coincidence that humans have evolved to have that master clock located just above the optic nerves, which relay information about incoming light via the brain.

“Circadian disruption is closely linked to cognitive dysfunction, fatigue, increase in inflammation, metabolic dysfunction, and GI disturbances,” said Christopher Colwell, PhD, a professor of psychiatry at UCLA and a researcher on circadian rhythms.

“Just think of the acute effects of jet lag. These are the symptoms of your circadian rhythms being disrupted. Over time (years), circadian disruption increases risk for heart disease and even cancer (breast cancer).”

Researchers have closely studied shift workers because their body clocks and circadian rhythms are sometimes completely disrupted by unnatural, changing schedules. Researchers have found they have increased risk of heart disease, diabetes, metabolic syndrome, obesity, and depression.

It's not only when you sleep but also whether you get enough deep and restful sleep that can upset your circadian rhythms and impact your health. Depression, anxiety, bipolar disorder, and other mental health conditions are frequently linked to, or worsened by, not getting good quality sleep regularly, according to the Sleep Foundation.

Sleeping in the dark to prevent obesity

It’s not just working at night that can throw your body’s circadian rhythms out of whack. A far more common reason people unwittingly disrupt their internal clock is sleeping in a room that’s not totally dark. In fact, the common habit of snoozing with a TV or computer left on, or sleeping in a bedroom with curtains that don’t block all light from outside, may contribute to the obesity problem in the U.S.

Research conducted by National Institutes of Health (NIH) scientists, involving data from almost 51,000 American women between the ages of 35 and 74, found a strong association between any exposure to artificial light at night while sleeping and weight gain. The study participants were asked if they slept with no light, a small nightlight, light outside coming through curtains, or a light or television on in their bedroom.

The link between light and weight gain varied with light exposure. The researchers found, after following the women for two to three years, a small, dim nightlight wasn’t linked to weight gain. Women who slept with a light or television on, however, were about 17 percent more likely to have gained a significant amount of weight (an average of 17 lbs.). The results suggest cutting off lights at bedtime could lower the risk of obesity.

The explanation again goes back to light at night interfering with circadian rhythms and the effect on the body.

"Humans are genetically adapted to a natural environment consisting of sunlight during the day and darkness at night," said NIH researcher Chandra Jackson, PhD. "Exposure to artificial light at night may alter hormones and other biological processes in ways that raise the risk of health conditions like obesity.”

Sleep-based ways to prevent and treat disease

Could sleep hold the key to ways to not only prevent but also treat many health problems? Neurologist Phyllis Zee, MD, PhD, director of the Center for Circadian and Sleep Medicine at Northwestern University thinks so. She and her colleagues are focused on multidisciplinary collaborative research to advance what she calls “sleep-based therapies for a broad spectrum of human disease.”

Their research has shown that sleeping with even a moderate amount of ambient light in the room negatively impacts your internal clock and harms cardiovascular function, kicking your heart into what the researchers call “high gear” with a fast heart rate. It also increases insulin resistance, which is a risk factor for diabetes, metabolic syndrome, and heart disease.

Some of the ways understanding circadian rhythms could benefit individual health may be surprising. A case in point: there really is something to the idea some people are “morning larks or night owls” — and their circadian rhythms vary. That’s important to pinpoint because certain medications and treatments are more effective if timed to a person’s circadian rhythms.

To that end, Zee and her team have developed the first simple blood test to identify an individual’s precise internal time clock as compared to the external clock time. The TimeSignature test looks for certain gene patterns that determine what time your body’s master clock thinks it is, the researchers explained.

The test will help scientists search for the impact of misaligned circadian rhythms in a range of diseases, including diabetes, cardiovascular disease, and Alzheimer's disease. When the blood test eventually is available to doctors, it could be a way to measure a patient’s internal biological clock to guide medication dosing at the most effective time for a person’s unique body.

“So many drugs have optimal times for dosing,” Zee explained. “Knowing what time it is in your body is critical to getting the most effective benefits. The best time for you to take your blood pressure drug or chemotherapy or radiation may be different from somebody else.”

Tips to help protect your internal body clock

If you’re a shift worker on rotations, don’t try to live in two different worlds. Friends and family need to know about the importance of uninterrupted daytime sleep, says the American College of Emergency Physicians (ACEP).

“An answering machine is a must for all shift workers. A dark, cool, quiet sleeping place increases both total sleep time and sleep quality. Blackout curtains are a worthwhile investment for all who must sleep during the day,” ACEP advises.

The organization also suggests a “split sleep” period — 3 to 4 hours just before and 3 to 4 hours just after a night shift. That way, at least part of every sleep cycle is during a circadian period

For everyone else who keeps a more normal sleep-wake schedule, sleep medicine expert Zee has tips for protecting your circadian rhythms:

• Keep lights off in the bedroom. If you must have a light on (which older adults may need for safety), make sure it is dim, and keep it close to the floor.
• The color of light plays a role in how disruptive it is to your internal clock. Amber, red, or orange light causes less stimulation to the brain during sleep. Don’t use white or blue light, and keep it far away anyone who is sleeping.

Can’t control outdoor light coming into your bedroom? Move your bed so the outdoor light isn’t on your face. If that doesn’t work, opt for blackout shades or eye masks.

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