We all know that sleep is an important part of our lives; it keeps us regular, it rejuvenates us during the night and it is central to a healthy metabolism. Sleep allows our bodies to function at peak efficiency and without it we get cranky, our reflexes are less sharp and our brains do not perform as quickly. Sleeping well also contributes to weight loss, since the more hours we get each night, the less we are exposed to the risk of becoming obese. How does something so simple contribute to overall weight gain prevention? The answer is in your hormones.

Weighty Research

Early findings of a study led by Professor Francesco Cappuccio at the University of Warwick Medical School in 2006 have linked lack of sleep with weight gain. Involving over 28,000 children and 15,000 adults, the study found that people who get less than five hours of sleep per night actually double their risk of becoming obese. Continued habits that shorten sleep hours contributed to a greater Body Mass Index and a wider waist circumference in subjects over time. Professor Cappuccio amounts the obesity risk to changes in hormone levels in the body, specifically ghrelin and leptin, due to the lack of sleep. In the future he plans to conduct further studies on short sleep durations to see whether fewer hours of sleep influences other diseases like diabetes or hypertension.

This is not the first study that has linked lack of sleep to obesity. In the same year (2006), the Division of Kinesiology’s Department of Social and Preventive Medicine at Laval University in Quebec conducted a study based on similar hypotheses and found that children who slept even an hour or two less than other children became more obese.

In 2004, Dr. Shahrad Taheri of the University of Bristol carried out a study on over 1000 adults to determine the same link between lack of sleep and obesity. Using collected data on the sleeping habits of the subjects involved, the study measured ghrelin and leptin hormone levels that were important to energy use and appetite. Being more obese than those who slept more regular hours (8 and up), it was discovered that individuals who slept fewer hours had higher levels of ghrelin and lower levels of leptin, and that these hormone changes occurred while they slept.

Hormone Hungry Hippos

The majority of research done linking obesity to lack of sleep blames ghrelin and leptin as the two major hormones responsible for the increased risk of weight gain, which are actually counterparts – ghrelin primarily stimulates appetite and leptin does the opposite.

The ghrelin hormone is produced by cells lining the stomach, usually increasing in number before meals and decreasing after. Ghrelin increases both food intake and fat mass through sending brain signals in the hypothalamus. Ghrelin is also responsible for revving up the “mesolimbic cholinergic-dopaminergic” reward link, which is a fancy way of saying ghrelin activates the part of your brain that responds to feel-good hedonistic rewards like food. Lack of sleep increases the levels of ghrelin in the body, increasing your appetite and letting you increase your food intake.

Leptin, on the other hand is produced by adipose tissue, otherwise known as fat. This hormone is responsible for regulating energy intake and energy use, controlling the decrease of appetite and the increase of metabolism. The cool thing about leptin is that they can bind themselves to the “Ventral Medial nucleus” of the hypothalamus, otherwise known as the satiety centre of the brain. This region serves to make you feel full after eating enough food, and higher levels of leptin mean better control over appetite.