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October 11th, 2010
03:01 PM ET

Light exposure may cause weight gain

Exposure to light at night may cause weight gain without a change in activity levels or increased eating, according to new research in mice. The study was published in the online edition of the Proceedings of the National Academy of Sciences.

Lead study author Laura Fonken, a doctoral student in neuroscience at Ohio State University, explained that her study involved three groups of mice: One group was exposed to a standard light/dark condition, one group was exposed to a dim light cycle and a third group was exposed to 24 hours of continuous light for eight weeks.

While the three mice groups were exposed to the same activity and food levels, Fonken said,  the mice exposed to more light gained more fat than the mice that lived in standard light conditions.

Why did the light-exposed mice gain weight? Fonken said the light exposed mice were eating during their normal rest periods, adding, “when we restricted their food to times when they would normally eat, we didn’t see the weight gain,” Fonken explained “This further adds to the evidence that the timing of eating is critical to weight gain.”

Explaining how this might apply to humans, Fonken said that the dim-light mouse group could be compared to human exposure to television or computer time and eating during screen time—rather than during a meal time–is not uncommon, which might explain human weight gain.Previous studies have shown higher body mass indexes and increased rates of cardiovascular disease in overnight shift workers, she said, another instance where eating during traditional rest periods may apply and add to weight gain.

Fonken said they are also looking the role of the hormone melatonin, and whether light may change the levels of melatonin, which is involved in metabolism and may play a role in interrrupting the genes that control when the mice feed and are active.


soundoff (97 Responses)
  1. FoolKiller

    Uh, hello? They have already determined that lack of sleep leads to weight gain... so all this study really proves is that mice can't sleep well with the lights on 24×7.

    October 14, 2010 at 15:11 | Report abuse | Reply
  2. profbam

    Mice are nocturnal. Everything is backwards: active period and feeding are during lights out.

    October 18, 2010 at 20:57 | Report abuse | Reply
  3. wow

    wow this is just unbelievable. i lost almost 9 pounds in a week! check out bit.ly/d8nxmX

    October 26, 2010 at 22:43 | Report abuse | Reply
  4. CitizenX

    The funny thing is that this study was pointless from the beginning. Even if it proved that exposure to light somehow increased weight, there are countless other influences that are also more influencial to weight gain. As ground-breaking as they may have expected this study to be, the biggest response possible would just be obese people and teenage girls eating exclusively in the dark. Which is actually depressing, which could easily lead them to eat more foo-err, "non-judgmental comfort".

    October 27, 2010 at 19:25 | Report abuse | Reply
  5. James

    I actually believed this whole concept when I saw it on TV but now reading off this, I have a different perspective. Perhaps there were a lot of faulties in the studies that we aren't aware of?.. I'm sure there a lot of people in the world that sleep during the day and have not gained a pound. e.g. – I'm a college student and in my semester breaks or holidays, I completely ruin my circadian rhythm and sleep all through the day and go on the internet at 4am, etc. I have never gained any weight! I think this is only applicable for those that eat a lot because of being awake all through the day and gaining weight due to imbalance in hormones.

    January 8, 2011 at 10:15 | Report abuse | Reply
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Get a behind-the-scenes look at the latest stories from CNN Chief Medical Correspondent, Dr. Sanjay Gupta, Senior Medical Correspondent Elizabeth Cohen and the CNN Medical Unit producers. They'll share news and views on health and medical trends - info that will help you take better care of yourself and the people you love.