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Press Release
Too much light at night at night may lead to obesity, study finds
Tuesday, October 12, 2010


(Photo: mike canon/STOCK.XCHNG)
Persistent exposure to light at night may lead to weight gain, even without changing physical activity or eating more food, according to new research in mice.

Researchers found that mice exposed to a relatively dim light at night over eight weeks had a body mass gain that was about 50 percent more than other mice that lived in a standard light-dark cycle.

"Although there were no differences in activity levels or daily consumption of food, the mice that lived with light at night were getting fatter than the others," said Laura Fonken, lead author of the study and a doctoral student in neuroscience at Ohio State University.

The study appears this week in the online early edition of the Proceedings of the National Academy of Sciences.

If the mice are not less active or eating more, what's causing the bigger weight gain? Results suggest that mice living with light at night eat at times they normally wouldn't.

In one study, mice exposed to light at night – but that had food availability restricted to normal eating times – gained no more weight than did mice in a normal light-dark cycle.

"Something about light at night was making the mice in our study want to eat at the wrong times to properly metabolize their food," said Randy Nelson, co-author of the study and professor of neuroscience and psychology at Ohio State.

If these results are confirmed in humans, it would suggest that late-night eating might be a particular risk factor for obesity, Nelson said.

In one study, mice were housed in one of three conditions: 24 hours of constant light, a standard light-dark cycle (16 hours of light at 150 lux, 8 hours of dark), or 16 hours of daylight and 8 hours of dim light (about 5 lux of light).

The researchers measured how much food the mice ate each day. They also measured how much they moved around their cages each day through an infrared beam crossing system. Body mass was calculated each week.

Results showed that, compared to mice in the standard light-dark cycle, those in dim light at night showed significantly higher increases in body mass, beginning in the first week of the study and continuing throughout.

By the end of the experiment, light-at-night mice had gained about 12 grams of body mass, compared to 8 grams for those in the standard light-dark cycle. (Mice in constant bright light also gained more than those in the standard light-dark cycle, but Nelson said the dim light-at-night mice were better comparisons to the light exposure that humans generally get.)

The dim light-at-night mice also showed higher levels of epididymal fat, and impaired glucose tolerance – a marker of pre-diabetes.

Although the dim light-at-night mice didn't eat more than others, they did change when they ate, results showed. These mice are nocturnal, so they would normally eat substantially more food at night. However, the dim light-at-night mice ate 55 percent of their food during the daylight hours, compared to only 36 percent in the mice living in a standard light-dark cycle.

Since the timing of eating seemed significant, the researchers did a second study, similar to the first, with one important difference: instead of having food freely available at all times, food availability was restricted to either the times when mice would normally be active or when they would normally be at rest.

In this experiment, mice exposed to the dim light at night did not have a greater gain in body mass than did the others when their food was restricted to times when they normally would be active.

"When we restricted their food intake to times when they would normally eat, we didn't see the weight gain," Fonken said. "This further adds to the evidence that the timing of eating is critical to weight gain."

The findings showed that levels of corticosterone, a stress hormone, were not significantly different in dim light-at-night mice compared to those living in a standard light-dark cycle.

That's important because corticosterone has been linked to changes in metabolism, Fonken said. This shows there doesn't have to be changes in corticosterone levels to have changes in metabolism in the mice.

So how does light at night lead to changes in metabolism? The researchers believe the light could disrupt levels of the hormone melatonin, which is involved in metabolism. In addition, it may disrupt the expression of clock genes, which help control when animals feed and when they are active.

Overall, the findings show another possible reason for the obesity epidemic in Western countries.

"Light at night is an environmental factor that may be contributing to the obesity epidemic in ways that people don't expect," Nelson said. "Societal obesity is correlated with a number of factors including the extent of light exposure at night."

For example, researchers have identified prolonged computer use and television viewing as obesity risk factors, but have focused on how they are associated with a lack of physical activity.

"It may be that people who use the computer and watch the TV a lot at night may be eating at the wrong times, disrupting their metabolism," Nelson said. "Clearly, maintaining body weight requires keeping caloric intake low and physical activity high, but this environmental factor may explain why some people who maintain good energy balance still gain weight."

###

Ohio State University: http://researchnews.osu.edu


Thanks to Ohio State University for this article.

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Comments
Cheshire

Guest Comment
Tue, Oct 12, 2010, 2:51 pm CDT

This is stupid, the mice with more food available ate it and gained more weight? YOU DON'T SAY! At that point your whole light/dark cycle thing becomes pointless, doesn't it?


Brian Krueger, PhD
Duke University
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Tue, Oct 12, 2010, 3:27 pm CDT

Cheshire said:

This is stupid, the mice with more food available ate it and gained more weight? YOU DON'T SAY! At that point your whole light/dark cycle thing becomes pointless, doesn't it?

The experiments sound well controlled and sound to me.  It's in PNAS, not some bottom tier grbage journal too.  The article specifically states that the mice with the altered light cycles ate NO MORE food than the other mice, yet gained more weight.  I think you should read the article again and see if it makes more sense a second time around.

Mlle. Vilain

Guest Comment
Wed, Oct 13, 2010, 6:54 pm CDT

This seems a little like a waste of resources.  I've been told since I can remember that late-night eating affects weight negatively.  While yes, the evidence is helpful, and the observations about it not being the amount of food so much as the rate of metabolism, it feels like more excuses for why people are overweight.

If this study is to continue, I would like to see the results with human test subjects, or at the very least creatures who are diurnal.

Guest

Guest Comment
Thu, Oct 14, 2010, 12:26 pm CDT

Contradiction in the article:

 

"Although there were no differences in activity levels or daily consumption of food, the mice that lived with light at night were getting fatter than the others," said Laura Fonken, lead author of the study and a doctoral student in neuroscience at Ohio State University.

 

In one study, mice exposed to light at night – but that had food availability restricted to normal eating times – gained no more weight than did mice in a normal light-dark cycle.

 

So although there were no differences in activity levels or consumption of food mice got fatter in light at night, yet those with light at night but had food restrictied to normal eating times gained no more weight then the other mice? O_o

Brittany

Guest Comment
Fri, Oct 15, 2010, 11:14 pm CDT

well I''m plus sized and don't like it completely dark at night (I sleep with a small light on) and Im starting to work out and eat better but according to this study i guess I'm doomed to be overweight for the rest of my life...stupid.

Guest

Guest Comment
Mon, Oct 18, 2010, 10:40 pm CDT

Guest said:

Contradiction in the article:

 

"Although there were no differences in activity levels or daily consumption of food, the mice that lived with light at night were getting fatter than the others," said Laura Fonken, lead author of the study and a doctoral student in neuroscience at Ohio State University.

 

In one study, mice exposed to light at night – but that had food availability restricted to normal eating times – gained no more weight than did mice in a normal light-dark cycle.

 

So although there were no differences in activity levels or consumption of food mice got fatter in light at night, yet those with light at night but had food restrictied to normal eating times gained no more weight then the other mice? O_o

Thats not a contradiction.

Think is over again.

Some of the mice had food all the time, and were exposed to light during the nighttime.  They gained weight, although they ate the same quantity of food overall.

The second group of mice ONLY had food during normal times, and were also exposed to light during the nighttime.  They didn't gain extra weight.

These paragraphs are making the VERY specific point that its not HOW much they eat, its WHEN they eat it.  and WHEN they eat it, if they have a choice, is based on the ambient brightness.

ERGO: Bright lights make you hungry so you eat.  Then you go to bed and it fucks up your metabolism because eating right before sleeping isn't a good idea.


Will
UC Davis
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Thu, Oct 28, 2010, 6:56 pm CDT

I actually think that this is a very good study, but I'm not sure that comparisons can be made between mice and humans.

Mice and humans have very different eating patterns.  Starting with the fact that mice are nocturnal eaters, and humans are not.  So comparissons are difficult to make between the two.

Mice also eat a lot of small meals throughout the night, while humans tend to eat 3 large meals (and maybe a couple of snacks) throught the day.  If the mice do not know when the night is because it is light all the time that means they will eat throughout the day, and therefore feed continuously.  They may not eat more, but they eat around the clock as opposed to at controlled times.  This is what they showed in the second experiment.

 


Nikkilina
Washington University School of Medicine
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Thu, Oct 28, 2010, 8:11 pm CDT

I think that's a good point Will. When I was at Pfizer it was a constant thing that we struggled with. It may seem obvious, but mice are not people. Anything that hasn't yet been translated into human studies need to be taken with a grain of salt.

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