Mammals, birds, many reptiles and most fish all share at least one common activity: sleep. The fact that so many creatures spend time sleeping is a pretty good indication that, like breathing and eating, sleep is essential to sustain life and health. Though the actual purpose of sleep is not completely understood, it’s during sleep that the body is busy making repairs and clearing out cellular debris, and it’s also when most of our growth takes place. And although a few nights without enough sleep won’t kill you, you will function poorly, with compromised motor skills, judgment, cognitive performance, depressed mood and immunity. Keep it up for years and long-term sleep deprivation will have numerous, far-reaching health consequences, playing a key role in the development of diabetes, cardiovascular disease, obesity and premature death.

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My advice? When it comes to sleep, don’t cut corners – give it its due every night because the lack of good sleep disrupts so many aspects of your health, including your metabolism and hormonal balance — each of which tends to reinforce the other. What exactly are the side-effects of poor sleep?

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Here are a few that are the most concerning:

Too much cortisol.  

Lack of sleep adds even more stress to an already stressed-out body. Excess cortisol is released which disrupts insulin response which in turn signals the body to hang on to fat rather than burn it.

Insulin resistance.  

The extra cortisol can throw your insulin response out of whack, so your excess hunger is often takes the form of cravings for sweet, starchy foods—which can over time encourage sugar addiction.

Glucagon shortfall.

Just as insulin tells your body to hang on to fat, glucagon cues the body to burn it.  Lack of sleep encourages glucagon levels to drop, which means there’s not enough glucagon available to keep that fat burning.

Decreased adiponectin.  

When you don’t sleep enough, there’s a drop in your body’s production of adiponectin, the hormone that promotes insulin sensitivity and fat break-down, which in turn can leave you more susceptible to problems with metabolism, inflammation and cardiovascular function.  

Not enough leptin.  

Leptin is the hormone that triggers feelings of fullness. When lack of sleep starts to lower your leptin levels, you don’t feel full as soon as you should and, as a result, you eat more.  

Too much ghrelin.  

When you short yourself on sleep, levels of the hunger-triggering hormone ghrelin start to rise, causing you feel hungrier than you should. The result? You eat more than you would if your ghrelin levels were sufficient and in balance.  

Insufficient human growth hormone (HGH).

HGH improves your fat metabolism and helps preserve or build lean muscle so when its levels drop, your weight can soar. To make enough of this hormone, which is made exclusively during the deepest stage of sleep, you’ve got to get long, uninterrupted sleep.

Leaky gut.  

During sleep, your body rebuilds the gut wall.  Lack of sleep promotes an imbalanced microbiome, a leaky gut, inflammation—and a number of troublesome symptoms like weight gain. Moreover, you rely on your gut and the bacteria that live in it (your microbiome) to make the biochemicals that your brain needs to orchestrate sleep. So once again, we’re back to balance: You need sleep to heal your gut, and you need a healthy gut to enable sleep.

Disrupted body clock.  

Researchers at the University of Manchester have discovered that when your body clock is disrupted, you develop inflammation—which cues your body to hold on to fat. A protein known as REVERB is also linked to your body’s clock—and REVERB helps to regulate both adiponectin and inflammation. As a result, when your body’s clock is thrown off—through irregular sleep cycles, changing time zones, or insufficient sleep—a number of interlocking factors encourage your body to hold onto fat.

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Bottom line: Good, restful sleep keeps you vigorous, energized, and at a healthy weight – so get yours today!

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Adapted from my book, How To Be Well: The 6 Keys to a Happy and Healthy Life.