Leaving the TV or lights on while sleeping may cause you to gain weight

Wow, it’s been a busy couple of weeks for studies linking poor sleep and circadian disruption to weight gain and impaired metabolism.  Last week I covered 2 of these studies: The first showing that varying your sleep schedule increases the risk of metabolic impairment and the second showing that people who sleep in on the weekends experience a larger drop in insulin sensitivity than those that are chronically sleep deprived.

Well today we have another study showing that women who are exposed to artificial light at night(ALAN) while sleeping are at an increased risk for obesity.  When you break it down it appears that the effect isn’t that large, only a 17% increased risk of gaining 11lbs in women exposed to ALAN compared to those who were not, but it was independent of other risk factors.  It also appears that select groups have more cause for concern than others and ALAN also appears to drive some poor behaviors, which I covered in the 2 studies mentioned above.

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Artificial Light at Night(ALAN) and weight gain: Cause for concern

The study followed 43,722 women to identify if those who slept with a light on a night were at an increased risk of being obese or becoming obese.  Since it’s an epidemiological study you really can’t say that ALAN causes obesity, only that women who are exposed to ALAN while sleeping are at an increased risk of obesity.

Some of the other findings were pretty telling.  At baseline, women who were exposed to ALAN in the form of a television or light on in the room while they were sleeping slept less, consumed a lower quality diet, performed less physical activity, and were more likely to snack at night.  Similar to the finding on people who slept in during the weekends, women who slept with a light or television on in their room had poorer habits that generally lead to obesity.

Other factors common with ALAN while sleeping increased the risk of gaining 11lbs or becoming obese.  This includes less total sleep, turning on a light at night, inconsistent sleep and wake times, taking sleep medications, and frequent napping.

The reason that ALAN drives this behavior is that it disrupts circadian rhythms.  Circadian rhythms drive behavior as well as the hormonal milieu within, and exposure to improper timesetting cues including light alters behavior and physiology in many ways that promote weight gain including decreasing insulin sensitivity and increasing hunger.

There were also some fairly interesting findings in the study.  For example, ALAN had a greater effect on gaining 11lbs in women who were normal weight or overweight at the beginning of the study than women who were obese.  ALAN also had a stronger effect on weight gain in women who were eating a higher quality diet and performing more physical activity.

The authors attribute the greater effect on ALAN on weight gain in women of healthy weight to a higher number of other risk factors in women who are obese.  In other words, ALAN has a greater effect on weight gain in women of a healthy weight because they are doing most things right.  The average follow up was 5.7 years, and most people are going to gain some weight in that timespan; 11 lbs isn’t out of the ordinary.

As we get older, specifically 30 years old and above, we are more prone to circadian disruption.  This isn’t something that we are destined for, it just means we need to avoid sending improper signals to the body.  By adjusting our exposure to timesetting cues called zeitgebers, we can optimize our circadian rhythms to prevent weight gain or lose it if we’ve already gained it.


On its own, this study really only tells us that artificial light at night may be an independent risk factor for gaining 11lbs or more over 5.7+ years.  But the other evidence that seems to be piling up indicates that improper light exposure may be something people should pay attention to if their goal is to maintain a healthy weight or to lose some excess.

Ultimately, I don’t think focusing on light exposure in isolation will yield amazing weight loss results.  Based on the other evidence, proper daily exposure to light with high levels of exposure during the day and elimination of exposure at night may be useful to drive behaviors that promote weight loss.  This includes higher levels of physical activity, less snacking at night, decreased hunger, and better sleep.

Still the evidence showing a stronger effect of ALAN on weight gain in women of a healthy weight should encourage people to avoid light exposure at night.  It’s important to point out that this study categorized light exposure at night in to 3 categories including a small night light, light outside of the room, and light/TV in the room.  The effects were stronger with light/TV on in the room than with a small night light or light on outside of the room.

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