Blackout curtains, sleeping masks, you name it — they all exist for a reason. Sleeping in the dark is simply better for you.
It can improve your sleep and therefore your day-to-day functioning. It can also improve your health.
Scientific studies have linked being exposed to light while sleeping to an increased risk for several serious health problems. Here is a look at them.
1. High blood pressure
A study of people aged 63 to 84 found that those who were exposed to any amount of light while sleeping were “significantly more likely” to have hypertension compared with those who were not exposed to any light while sleeping. The findings were published in Sleep, an academic journal of the Sleep Research Society.
For the purpose of the study, hypertension was defined as having a systolic blood pressure (the first number in a reading) of at least 140, a diastolic blood pressure (the second number in a reading) of at least 90 or taking medication for high blood pressure.
The study authors noted that high blood pressure is a risk factor for heart disease, but it’s also associated with other health problems, including vision loss and kidney disease.
2. Diabetes
The study published in Sleep also found that exposure to any amount of light while sleep significantly increased the chances of having diabetes, which the study authors defined as having a fasting blood glucose (sugar) level of more than 126 milligrams per deciliter (mg/dL).
Like high blood pressure, diabetes is a risk factor for heart disease, which is the No. 1 cause of death in the U.S. That means someone with diabetes is more likely to develop heart disease.
Diabetes is also a killer in its own right, ranking among the top 10 causes of death.
3. Obesity
The study published in Sleep also found that exposure to light while sleeping significantly increased the chances of being obese.
Obesity is defined as having a body mass index (BMI) of 30 or greater. BMI is a measure of body fat based on height and weight.
The study authors noted that obesity is a risk factor for heart disease. It also increases your risk of developing myriad other health problems, including high cholesterol, asthma, sleep apnea, osteoarthritis, gallstones and gallbladder disease.
4. Increased blood sugar
A study of young adults by researchers from Northwestern University’s medical school found that sleeping with an overhead light on (moderate lighting, or 100 lux) for even one night is enough to increase insulin resistance the next morning, when compared with sleeping in a dimly lit room (less than 3 lux). Their findings were published in PNAS, an academic journal of the National Academy of Sciences.
Insulin resistance is when the cells in your muscles, liver and fat don’t properly respond to insulin and so can’t use glucose from your blood to gain energy.
When this happens, your pancreas makes more insulin, pushing your blood sugar up over time. Over time, high blood sugar can permanently damage your eyes, nerves, kidneys and blood vessels.
5. Increased heart rate
The Northwestern University study also found that sleeping with a moderate amount of light activates the autonomic nervous system, which regulates your internal organs. As a result, your nighttime heart rate increases, interfering with your body’s ability to go into restoration mode.
“Even though you are asleep, your autonomic nervous system is activated. That’s bad,” study co-author Dr. Daniela Grimaldi said. “Usually, your heart rate together with other cardiovascular parameters are lower at night and higher during the day.”
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