The advice of turning off the lights and closing the curtains is gaining more scientific credibility.
Many Americans sleep in a room with artificial light, whether it is a TV or a streetlight.
One night of sleep with just a moderate amount of light may have adverse effects on cardiovascular and metabolism.
I was surprised that small amount of light just getting through the eyes to the brain still had such notable effect.
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The study was conducted to measure the effects of 100 lux of artificial light on healthy adults while they were sleeping.
This is about enough light that you could see your way around, but it isn't enough light to read comfortably. The participants slept in a mostly dark room on their first night in the study. Half of them slept in a room with a light overhead.
The researchers ran tests on the sleepers and recorded their brainwaves, heart rates, and blood pressure. They would give both groups a big dose of sugar in the morning to see how their systems responded to the spike.
The results of the study were published in the Proceedings of the National Academy of Sciences.
The group that was exposed to the light had higher heart rates than those who spent both nights in the dark. They had more trouble getting their blood sugar into a normal range because they had increasedinsulin resistance in the morning.
Being exposed to light at night could affect our metabolism.
It is supported by research that having the light on can disrupt the quality of sleep, but this study did not find that result while monitoring the people in the lighted room. The participants generally thought they slept well.
melatonin is a hormone that helps with the timing of melatonin and promotes sleep. During the day, melatonin is suppressed and rises at night.
Scientists have found a link between melatonin levels and several diseases, including cancer and diabetes, and studies show artificial light at night can suppress melatonin levels. The study didn't find evidence that melatonin levels were lower among people sleeping with the light on.
The light level that was getting through the eyes probably wasn't bright enough to suppress melatonin.
The light was enough to cause the sympathetic arm of the nervous system to fire. When the body moves into a parasympathetic state, it is supposed to cool down during sleep.
The small amount of light is thought to have shifted the nervous system to a more alert state.
It is almost like the brain and the heart know that the individual is sleeping.
Dr. Chris Colwell's lab at UCLA studies the mechanisms underlying the sleep-wake cycle and the study is an example of how even relatively dim light exposure can be disruptive.
The findings make sense because of the daily rhythm of the autonomic nervous system.
Colwell says that there is a lot of coordinated actions that have to occur in order for us to get a good night's sleep.
The effect on the nervous system was not dramatic, but it was still concerning.
The study found that metabolic health suffered.
Colwell notes that there is a solid pool of research that shows that disrupting the rhythms of the body makes it harder to regulate blood sugar levels.
Some human studies have used a brighter intensity of light than people are used to. Colwell suspects the harmful effects would be cumulative, since this was only one night, so imagine if you were living that way constantly.
The suprachiasmatic nucleus is the master clock of the body, but organs and tissues have their own cellular timekeeping devices. One example is cells in the pancreas. The sleep-wake cycle can be disrupted, which can affect their ability to regulate their blood sugar.
Dr. Charles Czeisler is the chief of the Division of Sleep and Circadian Disorders at the Brigham and Women.
A large observational study of more than 40,000 women found that sleeping with a TV or light on was associated with an increased risk of gaining 11 lbs over the course of five years.
For longer than one night, Cseizler has looked at the consequences of disruptions in the rhythms.
He and his colleagues found that the negative effects on metabolism observed in their study participants over the course of three weeks were not due to sleep deficiency, but due to disruptions to the circadian rhythms.
When we did not increase their exposure to artificial light at night, we did not see the effects of chronic sleep deficiency.
It is not to say that sleep deficiency does not have adverse effects on health, but it is to say that being exposed to light at night underscores the far-reaching consequences.
Cseizler says that people think that as long as they fall asleep and are unconscious, it doesn't have any effects.
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