Electric car maker Tesla’s CEO Elon Musk. (Jack Plunkett/AP)

An apparently overworked, under-rested Elon Musk rejected Arianna Huffington’s recent suggestion that he get more sleep — and he did so in a tweet in the middle of the night.

The Tesla chief executive told the New York Times last week that he has been working a lot — up to 120 hours per week lately — saying, “There were times when I didn’t leave the factory for three or four days — days when I didn’t go outside.”

When he has time to sleep, he told the Times, he often has to take Ambien, a potent sedative. In a tweet last year, he wrote: “A little red wine, vintage record, some Ambien . . . and magic!”

It prompted Huffington, a longtime sleep advocate who co-founded the HuffPost, to reach out and offer her fellow entrepreneur some tips.

“People are not machines,” the business executive told Musk in an open letter posted last week on her website Thrive Global. “For machines — whether of the First or Fourth Industrial Revolution variety — downtime is a bug; for humans, downtime is a feature. The science is clear. And what it tells us is that there’s simply no way you can make good decisions and achieve your world-changing ambitions while running on empty.”

Huffington tweeted out the letter Friday, urging the Tesla executive to change his ways.

His response?

“Ford & Tesla are the only 2 American car companies to avoid bankruptcy,” he wrote Sunday in a tweet to Huffington. “I just got home from the factory. You think this is an option. It is not.”

In her open letter to Musk, Huffington, who wrote a 2016 book titled “The Sleep Revolution,” cited research suggesting that sleep deprivation can lead to cognitive impairment. According to the Mayo Clinic, adults need seven to nine hours each night.

“You’ve come up against incredible challenges, and you’ve met them by being ever more rigorous and determined about applying the latest science,” Huffington wrote in the open letter to Musk. “But at the same time, you’re demonstrating a wildly outdated, anti-scientific and horribly inefficient way of using human energy. It’s like trying to launch us into our clean energy future (or into space) with a coal-fired steam engine. It just won’t work.”

Huffington said that she wrote to Musk in an open letter because the issue does not pertain to only him.

“It’s about the deeply entrenched delusion in our culture that burning ourselves out is the price we have to pay for success,” Huffington said in a statement Monday to The Washington Post.

“This is not about sleep, or about slowing down, or about asking Elon to chill out under a mango tree,” she said. “It’s about how we can unlock and sustain our peak performance, and see solutions and opportunities where others can’t.”

Musk did not immediately respond to a request for comment on the open letter.

Earlier this month, Musk apologized for calling an analyst‘s questions “boneheaded” and “boring” — blaming his behavior partly on his lack of sleep.

“I’d like to apologize for being impolite on the prior call,” Musk said Aug. 1, according to Business Insider. “Honestly, I really think there’s no excuse for bad manners, and I was kind of violating my own rule in that regard. There are reasons for it in that I had gotten no sleep, had been working 110 hour, 120 hour weeks, but nonetheless, there’s still no excuse.”

Other successful business executives have said that they, too, have worked long hours.

As the Atlantic reported this month, PepsiCo chief executive Indra Nooyi is known for her 20-hour days.

Former Yahoo president and chief executive Marissa Mayer has said when she was starting out at Google, she sometimes worked 130 hours and pulled at least one all-nighter per week.

“The actual experience was more like, ‘Could you work 130 hours in a week?‘ The answer is yes, if you’re strategic about when you sleep, when you shower, and how often you go to the bathroom,” Mayer told Bloomberg News in 2016.

Even President Trump has said that he sleeps only about four to five hours per night.

Virgin Group founder Richard Branson said he works hard, as well — but he does rest.

“It’s in bed and lights out hopefully by 11 p.m.,” he wrote on his blog. “I typically need five to six hours sleep to get the most out of my days.”

As The Washington Post’s Lenny Bernstein and Lena H. Sun reported earlier this year, though research has shown some people can get by on a small amount of sleep, many cannot.

The Washington Post reported:

Research has shown that there are rare individuals who function well on four to six hours of sleep, said Ying-Hui Fu, a professor of neurology and neuroscience at the University of California at San Francisco, who has studied the regulation of sleep for 20 years.

But for the vast majority of others, long-term sleep deprivation is a serious threat to well-being. It weakens the immune system and is associated with higher levels of metabolic problems, including diabetes, she said. Cognitive function and energy-level decline and the risk of depression and dementia increase, Fu said, because the brain and body aren’t given enough time to flush waste products and replenish resources.

“Sleep is one of the most important things for our survival,” Fu said. “I would say right after air and water . . . and before any food.”

Medical experts agree that sleep deprivation may be associated mental and physical health issues.

According to the Division of Sleep Medicine at Harvard Medical School, studies have shown that inadequate sleep can lead to weight gain and obesity, diabetes, high blood pressure and heart disease, as well as depression, anxiety and other mental issues.

“In addition to the feeling of sleepiness and changes in brain activity that accompany a night without sleep, other measures of performance are noticeably altered,” according to Harvard. “Concentration, working memory, mathematical capacity, and logical reasoning are all aspects of cognitive function compromised by sleep deprivation. However, not all of these functions rely on the same regions of the brain, nor are they impacted by sleep deprivation to the same degree. For example, the region of the brain known as the prefrontal cortex (PFC) is responsible for many higher-level cognitive functions and is particularly vulnerable to a lack of sleep. As a result, people who are sleep deprived will begin to show deficits in many tasks that require logical reasoning or complex thought.”

In her statement to The Post, Huffington said that Musk’s reply that slowing down isn’t an option presents a “false choice.”

“It’s impossible for any business to scale when it’s dependent entirely on the 24/7 presence and control of every element by the founder,” she said. "Building a leadership team and effectively delegating (the way Elon has done at SpaceX), cannot be done while you’re running on empty. And this is true for all us.”

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