Study offers evidence that insomnia, weight gain are linked

Q: I've been suffering from insomnia for the past year or so. I've also gained 15 pounds over the same time period. Could the two be connected?

A: I spoke about this with my colleague Dr. Stuart Quan, professor of sleep medicine at Harvard-affiliated Brigham and Women's Hospital. He confirmed that there is growing evidence of a link between obesity and insufficient sleep.

The growth of this country's obesity epidemic over the past 40 years, for example, correlates with a decline in the amount of sleep reported by the average adult. And in large population-based studies, obesity has been linked to less sleep.

But how might sleep deficiency be related to weight gain?

A recent study published in the journal Sleep provides some clues. Researchers studied a group of young, healthy adults over the course of four nights. One group was restricted to 4.5 hours of sleep per night; the other group got 8.5 hours of sleep per night.

At the end of the study, the researchers measured two hormones responsible for hunger: ghrelin (which increases appetite) and leptin (which reduces appetite).

In the sleep-restricted group, the ratio of the two hunger hormones was altered to favor greater appetite.

Other studies have observed the same thing. However, this study measured something more. Snack consumption - particularly items with more fat and protein - was higher after sleep restriction. And, strikingly, levels of appetite-stoking chemicals like ghrelin were higher at the time of greater snack consumption. These chemicals also stimulate reward centers in the brain.

So not only does sleep restriction make you hungrier, it also makes the act of eating more satisfying. In the face of this one-two punch, your willpower doesn't stand much of a chance.

This exciting finding requires further investigation, but it already supports existing evidence that sufficient sleep is important for optimal health. In particular, adequate sleep is important for combating obesity.

Not getting enough sleep regularly is also associated with many health problems besides obesity.

Difficulty thinking and depressed mood are two consequences. So is an increased risk of accidents and resulting injuries. Heart problems are more common. Inflammation in the body is encouraged by sleep deprivation.

The immune system is affected. For example, people do not get the same protection from vaccines when they are chronically sleep-deprived. Finally, the risk of getting Type 2 diabetes may be higher - even if chronic sleep deprivation does not result in obesity.

How much sleep do we need?

People are different: Some need more sleep than the average person, and some need less. For adults ages 26 to 64, seven to nine hours are recommended. For adults ages 65 or older, it's seven to eight hours.

So I do think there is likely a connection between your insomnia and weight gain.

The former could be leading to the latter - and both of them could be caused by depression and anxiety.

Talk to your doctor; there could well be a treatment that would improve your mood, help you lose weight - and give you a good night's sleep.

• Dr. Komaroff is a physician and professor at Harvard Medical School. For questions, go to AskDoctorK.com.