Yes, there is a correlation. There have been over 4 major studies each with thousands of patients showing a link between the amount of sleep you get and your weight. The cutoff is 7 hours. If you sleep less than 7 hours you are more likely to be overweight. It is also true that if you sleep too much or more than 9 hours you are also more likely to be overweight.
When a study tells us a medical fact such as sleep under 7 hrs being correlated with overweight, I always have to ask myself, if it is true and sensible or is this just a statistical correlation? This one is sensible. Too little sleep affects us in 2 ways. First, we have a hormone called ghrelin which comes from the stomach and sends signals to our brain that we are hungry. With less sleep, the ghrelin signal is amplified (stronger) and we are therefore hungrier. This is seen most commonly in shift workers as they change shifts and are up at hours that they used to sleep and are trying to sleep when they should have been awake. The second is lack of sleep is a stressor on the body. Our body reacts to stress by increasing cortisol (a hormone) or changing its activity. This change in cortisol increases our blood sugar and we gain weight (even on fewer calories). We gain weight often even when following a diet.
There are many sleep disorders that I see on a regular basis. Some are behavioral in that many of us are habitually poor sleepers with bad “sleep hygiene”. We drink too much caffeine, drink too much alcohol, work till 11 pm or try to catch up with sleep on the weekends (resetting our internal clocks), etc. Some are secondary to medical problems such as obstructive sleep apnea or restless leg syndrome. If you are a poor sleeper and overweight or obese, it is worth discussing sleep with your physician to best determine the way to improve your sleep quantity and quality.
Finally, beyond weight gain we now know that lack of sleep increases strokes and heart attacks. See recent study from the Archives of Internal Medicine. Those who sleep less than 7 and a half hours per night had 33% more strokes, heart attacks and sudden cardiac death. Isn’t an extra hour of sleep worth it? Considering the alternatives, it is almost priceless.