In this busy world we live in, it’s not easy to go to bed early. There are bills to pay, online shopping to do, work or chores to finish. Or maybe you simply can’t fall asleep when you go to bed too early. Then, of course, people who work the night shift must stay up all night.
But whether you’re a night owl or a morning dove, your internal clock pays the price of those late nights. When this clock is working like it’s supposed to, it keeps what scientists call a circadian rhythm. However, when something throws off your circadian clock, your whole body may suffer.
Understanding Circadian Rhythm
The machinery of your internal clock was originally set according to a day-night cycle that helps synchronize many of the processes that happen in your body. If you expose your body to light at night, it pushes your circadian rhythm out of balance.
It was once thought that your internal circadian clock was located only inside the hypothalamus of your brain. Now scientists are realizing that circadian timers exist in other brain regions, as well as in the tissues of your body.1 In fact, all cells have a circadian clock responsible for keeping time in the cell. You even have circadian-clock genes!
Your circadian clock is controlled by light. When sunshine or artificial light shines on the retina, a signal is sent to the hypothalamus, which then orchestrates a number of biological rhythms: whether to sleep or stay awake as well as hunger, body temperature and the secretion of hormones.
When your circadian clock gets thrown off, it’s no laughing matter. Scientists have found that disrupted circadian rhythm is linked to heart disease, depression and cancer. And it might very well explain why you can’t lose weight, even when you’re faithful to your diet.
Your Internal Clock and Your Heart
There’s a lot of scientific evidence to show that if your circadian rhythm is disrupted, you’re putting yourself at risk for cardiovascular disease—both heart attacks and strokes.
That evidence starts with the timing of certain heart-related events. Heart attacks happen two to three times more often in the morning compared to at night.2 Sudden cardiac deaths also have a circadian pattern, often occurring in the early morning.3 And atrial and ventricular arrhythmias (irregular heart rhythms) have circadian patterns, happening more often during the day compared to at night.4
In addition, circadian clock genes are expressed in the hearts of animals and humans. When scientists removed the circadian clock genes from heart cells of mice, the researchers observed that the animals had abnormal electrocardiography and their hearts were more susceptible to abnormal heart rhythms.5 Mice without clock genes also were less able to metabolize cholesterol properly and were more likely to develop atherosclerosis.6
The circadian clocks in heart cells must communicate with the central circadian clock in the hypothalamus in order to work correctly. When normal day-night cycles are interrupted—whether by jet lag, a late night out on the town or a long night at the computer—the communication between your central circadian clock and the one in your heart cells is interrupted. This leads to a number of chain reactions that can ultimately lead to cardiovascular disease.
For example, one group of researchers exposed mice to enough light throughout the day and night to disrupt their circadian rhythm. The mice’s hearts had abnormal structure and function and there was an altered expression of circadian clock genes, as well as other genes important to the functioning of the heart. Restoring the mice to a normal 24-hour daily rhythm made the negative changes go away, suggesting that “maintaining a normal rhythm is crucial to cardiovascular health.”5,7
Researchers conducted a similar experiment in a mouse model of heart attacks. They found that disrupting the mice’s circadian rhythm after a heart attack reduced the ability of the heart to heal. When circadian rhythms were normal throughout the course of healing after a heart attack, the heart’s structure and function were better preserved during the healing process.8
Circadian rhythm is also responsible for the normal variations in blood pressure that occur throughout the day. When circadian rhythm was disrupted in human subjects by exposing them to a 28-hour day for eight days, they developed high blood pressure and other heart problems.9
Because of circadian rhythm, certain heart medications are more effective when you take them at night. Researchers found that patients who took at least one regular antihypertensive medication at bedtime were more likely to have controlled blood pressure and were less likely to die from cardiovascular disease, as compared to patients who took the drugs in the morning.10
Circadian Rhythm and Depression
If your circadian rhythm is thrown out of balance, your mood may suffer. This can happen in the short days and long nights of winter. During this time of year, susceptible people suffer from a condition known as Seasonal Affective Disorder, or SAD for short.
Normally, your pineal gland secretes the most melatonin at night in response to darkness. However, people who suffer from SAD continue to secrete melatonin into the morning.11 When people who have SAD expose themselves to early morning bright light, which turns off melatonin production, they feel much better.12 (Interestingly, a small group of people can suffer from summer seasonal depression. One reason for this is because people stay indoors during excessively hot weather.)
It’s not just people who have Seasonal Affective Disorder whose mood improves after exposure to light. Even people who have regular depression may have lack of daylight to blame. Scientists have found that people who are depressed don’t get outside during the daytime as much as non-depressed people, especially in the morning, either because of winter weather, sleeping late or other behavioral or work-related factors.13
Regardless of the time of the year, exposing depressed people to morning bright light as well as manipulating sleep times successfully treats depression, according to the results of at least one study.14
And even if you’re not currently suffering from depression, if your bedroom isn’t dark enough at night, your mood could be at risk of taking a serious nosedive. That’s because people who are depressed are more likely to sleep in a room that’s not completely dark.
In one study, researchers measured the amount of nighttime light in the bedrooms of 516 elderly individuals. The depressed elderly people were exposed to more light at night compared to the non-depressed people. The depressed people were exposed to a greater intensity of light at night for a longer period of time than the non-depressed group. The researchers concluded, “The risk of depression may be reduced by keeping nighttime bedroom dark.”15
Circadian Rhythm and Cancer
More and more evidence continues to build that disrupted circadian rhythm is linked to cancer. Even the World Health Organization (WHO) International Agency for Research on Cancer (IARC) has listed circadian disruption caused by shift work as a carcinogen.16
One study based on 1996-2002 data concluded that breast cancer incidence was significantly linked to artificial light at night.17
Another study compared the rates of several different cancers between geographical areas that were exposed to a lot of artificial light at night and areas exposed to a smaller amount of light at night. After adjusting for other risk factors, the researchers found that breast cancer occurred more often in urban and rural areas where people were exposed to the most light at night, as compared to areas that weren’t as illuminated at night. There was no association between other types of cancer and light at night.18
The news is just as bad in studies looking at how shift work affects the risk of cancer. One group of researchers reviewed the medical literature. They examined a total of 28 studies, 15 on shift work, seven on short sleep duration, three on flight attendants and six on light at night.
In people who were employed as shift workers or flight attendants, there was a strong link between circadian rhythm disruption and breast cancer risk. Each 10-year increment of shift work was linked to a 16 percent higher risk of breast cancer.19
Further proof that messing with your circadian rhythm can lead to cancer can be found in two additional studies. In one of the studies, in mice with tumors, a severe disruption in the central circadian clock caused tumor growth to speed up.20 In the other study, cancer patients who maintained normal 24-hour circadian rhythms generally had a better prognosis than patients who had disrupted circadian rhythms.21
Circadian rhythms also affect the efficacy of cancer drugs. The circadian timing of when anticancer drugs are administered plays an important role in how well they work.22
Are Those Late Nights Causing Your Weight Gain?
Your circadian rhythm also controls your body weight. For example, mice exposed to dim lights at night have a higher body mass.23 Humans aren’t immune to the effects of light at night, either. One group of scientists studied more than 100,000 women and found there was a strong link between increasing levels of light at night and obesity. The more light at night the women were exposed to the higher their body mass index, waist:hip ratio and waist circumference.24
An earlier study reached a similar conclusion. Elderly people who were exposed to artificial light at night weighed significantly more and had a higher body mass index and waist circumference. They also had higher triglyceride levels and levels of LDL cholesterol, while levels of their HDL cholesterol were significantly lower.25
Restoring Your Rhythm
If your circadian rhythm is off beat, there are a number of things you can do to get it back into balance. First, unless you’re a shift worker, try to be in bed in a dark room by 11:30 p.m.
Second, choose to use a landline in your home instead of relying exclusively on a cell phone, as using cell phones more than two hours per day lowers melatonin levels.26
If you’re going to read before bedtime, read only printed books. People who used an eBook reader before bedtime took longer to fall asleep and weren’t as sleepy. They also had reduced melatonin secretion, their circadian clock was thrown off and their next-morning alertness was reduced compared to people who read a printed book.27
Exercise helps, too, as long as you don’t exercise too close to bedtime. Studies have shown that exercise can help reset your circadian clock.28
While avoiding light at night is important, exposing yourself to outside light in the morning is just as critical. This can help relieve symptoms of depression and seasonal affective disorder or stop even these two conditions from developing in the first place.
Two supplements are especially effective in resetting your circadian clock. The first is 5-hydroxytryptophan (5-HTP), which is a precursor to the mood-boosting hormone serotonin.29 Serotonin helps translate the light that hits the retina of your eye into a message your circadian clock can understand in order to keep it functioning properly.30 Melatonin also is made from serotonin.
Another supplement that can wind up the batteries of your circadian clock is melatonin. Studies show that circadian clock genes respond to melatonin supplementation by restoring daily rhythms.31
In Alzheimer’s patients, who often suffer from insomnia, supplementing with prolonged-release melatonin resulted in better cognitive performance compared to those patients treated with placebo. Sleep also improved in the subjects taking the melatonin.32
In another study of depressed people who weren’t sleeping well, melatonin reduced the depression scores of the subjects and improved their sleep.33 Plus, giving mice melatonin protected the animals against the harmful effects of obesity,34 meaning it may protect against those extra pounds that pile up as a result of too many nights burning the midnight oil.
You’ve Got Rhythm
At first glance, staying up past midnight may seem harmless. But it doesn’t take many late nights to send your circadian rhythm into a tailspin. And once that happens your heart, your mood and your plans to fit into your favorite jeans may all suffer.
By putting into practice the lifestyle measures in this article and taking 3-5 mg of melatonin and/or 150-300 mg of 5-HTP, you can reset your circadian rhythm and protect your body from some scary diseases.
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- Culić V. Int J Cardiol. 2014 Jun 15;174(2):417-9.
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- Pan X, et al. Circulation. 2013;128:1758-69.
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- Scheer FA, et al. Proc Natl Acad Sci U S A. 2009 Mar 17;106(11):4453-8.
- Hermida RC, et al. Chronobiol Int. 2010 Sep;27(8):1629-51.
- Wehr TA, et al. Arch Gen Psychiatry. 2001 Dec;58(12):1108-14.
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- Obayashi K, et al. J Affect Disord. 2013 Oct;151(1):331-6.
- Straif K, et al. Lancet Oncology. 2007 Dec;8:1065-66.
- Rybnikova N, et al. Chronobiol Int. 2015 Jul;32(6):757-73.
- Kim YJ, et al. Chronobiol Int. 2015 Jun;32(5):657-67.
- He C, et al. Int Arch Occup Environ Health. 2015 Jul;88(5):533-47.
- Filipski E, et al. Cancer Causes and Control. 2006;17(4):509-14.
- Mitchell MI and Engelbrecht A. Journal of Toxicology. 2015;Article ID 392360.
- Sothern F, et al. Journal of the National Cancer Institute. 1989;81(2):135-45.
- Aubrecht TG, et al. Chronobiol Int. 2015 May;32(4):557-60.
- McFadden E, et al. Am J Epidemiol. 2014;180(3):245-50.
- Obayashi K, et al. J Clin Endocrinol Metab. 2013 Jan;98(1):337-44.
- Shrivastava A and Saxena Y. Indian J Physiol Pharmacol. 2014 Oct-Dec;58(4):395-9.
- Chang AM, et al. Proc Natl Acad Sci U S A. 2015 Jan 27;112(4):1232-7.
- Tal-Krivisky K, et al. Physiol Behav. 2015 Aug 4;151:441-447.
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