Elon Musk says grueling 120-hour work weeks are taking a toll on his health. Here’s what sleeping less than 7 hours a night can do to you.

• Elon Musk says he doesn’t get much sleep.
• In an interview with the New York Times, Musk revealed he frequently logs 120-hour work weeks and doesn’t leave the Tesla factory for days at a time.
• Science suggests that sleep deprivation is a recipe for disaster. Here’s what we know about how a lack of sleep affects your body and brain.

Elon Musk seems exhausted.

The Tesla CEO told the New York Times that he’s been logging 120-hour work weeks lately, and it’s taking a toll on his well-being.

“It’s not been great, actually,” Musk told the Times. “I’ve had friends come by who are really concerned.”

He even missed out on his own birthday this summer and only carved out a few hours away from the factory for his brother’s wedding. Musk also said he hasn’t taken more than a full week off of work since 2001, when he got malaria.

If Musk is truly working 120-hour weeks on a regular basis, that means his work days are a minimum of 17-plus hours - seven days a week.

"There were times when I didn't leave the factory for three or four days - days when I didn't go outside," he told the Times.

Based on Musk's own numbers, there are only a maximum of seven hours per day that he's not working. So he's almost certainly getting far less than seven hours of shut-eye per night.

In the US, the Centers for Disease Control and Prevention (CDC) recommends all adults from 18-60 years old get at least seven hours of sleep a night, because getting less than that can set you up for "obesity, diabetes, high blood pressure, coronary heart disease, stroke, frequent mental distress" and death. But CDC surveys suggest Musk isn't the only bleary-eyed one out there not following the advice: about a third of adults in the US aren't getting their recommended dose of sleep.

The dangers of sleep deprivation

Sleep expert and neuroscientist Matthew Walker, who directs the sleep and neuroimaging lab at UC Berkeley, studies what a lack of sleep can do to a person's body. He regularly gives sleep advice to the NBA, NFL, and Pixar, among others.

Walker recently summed up his overall stance on snoozing for Business Insider: "The shorter your sleep, the shorter your life."

That's not hyperbole -Walker's research suggests that routinely getting only six or seven hours of shut-eye per night can do serious long-term damage to your health, and in some cases even kill you. He believes everyone should aim for between seven and eight hours a night on the pillow.

Walker is such an evangelist about this, that in his own life, he gives himself a strict eight hours of "sleep opportunity" each night. That means he's in bed for at least eight hours, even if he spends a portion of that time falling asleep and waking up. He says that schedule helps keep him productive, as well as emotionally and physically fit.

How getting less than seven hours of sleep affects your body and brain

If you're not sleeping enough, "you will be both dead sooner, and the quality of your life will be significantly worse," Walker told Business Insider. Here's why.

• Sleep deprivation depletes stores of your "natural killer cells," a type of lymphocyte (white blood cell) that nix tumor and virus cells. A single 4- or 5-hour night of sleep could lower your body's "natural killer" cell count by around 70%, Walker says.
• Missing sleep can put your body on a crash course for chronic disease. Insufficient sleep has been linked to increased instances of Alzheimer's, obesity, stroke, and diabetes. Lack of sleep also changes how insulin operates in your body and how quickly your cells absorb sugar. After a week of sleep-deprived nights (five or six hours), your doctor could diagnose you with pre-diabetes, Walker says. That means your blood-sugar levels are elevated enough that you're on track to become a diabetic. Long-term damage to your heart, blood vessels, and kidneys could already be in motion.
• Insufficient sleep makes the body a better breeding ground for cancer. Sleepiness is now being blamed for cases of colon cancer, breast cancer, and prostate cancer. An off-kilter sleep schedule may also give rise to cancer, since it causes melatonin to be suppressed. The World Health Organization calls night work a "probable carcinogen."

Of course, not everybody's body works in exactly the same way.