Millions of Americans aren’t getting enough shut-eye.

Nearly one in three adults in this country get an average of less than seven hours of sleep a night, according to a study released this week by the Centers for Disease Control and Prevention. While overall, 65.2% of adults got seven or more hours of sleep a night — that’s what the CDC recommends — people 65 and older were more likely to get enough sleep, as were non-Hispanic whites (66.8%), Hispanics (65.5%), and Asians (62.5%).

Source: CDC

For the most part, people living in the eastern part of the country were more sleep deprived than those in the central and western part of the country. Residents of Hawaii get the least sleep (just over 56% get seven or more hours a night), while residents of South Dakota get the most (71.6%).

The CDC cautions that getting too little sleep can put your health at risk. “Sleeping less than 7 hours per night is associated with increased risk for obesity, diabetes, high blood pressure, coronary heart disease, stroke, frequent mental distress, and all-cause mortality,” the report reveals.

Interestingly, while it used to be that 8 hours of sleep a night was the Holy Grail, new research is challenging that notion.

For many years, some experts have espoused that humans need eight hours of sleep a night, in part because they believed this is what our ancestors got. The thinking was that artificial light — from things like electricity, as well as TV, Internet and smartphones — has disrupted our sleep from what was natural.

But a study published in 2015 in the journal Current Biology challenges that thinking. The scientists examined the sleep patterns over more than 1,100 nights of three preindustrial, hunter-gatherer societies — the Hadza tribe in Tanzania, the San in Namibia and the Tsimane in Bolivia — and found that people in each of these societies slept for an average of about 6.5 hours a night.

They also rarely nap, taking a daytime snooze on just 7% of the days in winter and 22% in summer. “The sleep in these traditional human groups is more similar to sleep in industrial societies than has been assumed,” the authors write. “They do not sleep more than most individuals in industrial societies.”

Wake-up call for America's sleep-deprived

Other recent studies also show that the 8-hours-of-sleep rule may be outdated, but for a different reason. Some scientists tout this rule because they believe that’s the magic amount of sleep that can help prevent issues like disease and obesity. But in a study of 450 elderly women published in the journal Sleep Medicine, researchers — who tracked the women over 10 years — found that women who slept more than 6.5 hours (and less than 5) a night had higher mortality.

Another study published in the Archives of General Psychiatry, which tracked 1.1 million people in a cancer study, found that people who slept between 6.5 and 7.4 hours a night (vs. those who slept more or less) had the lowest mortality rate.

Getting 8 hours may not improve your mental acuity either. A study published in the journal Frontiers in Human Neuroscience found that cognitive performance — in this study, it looked at how more than 200,000 people performed on spatial-memory, matching and arithmetic tests on the Luminosity site — peaked after about 7 hours of sleep, then started dropping.

There is certainly still evidence that 8 hours is good, and the Centers for Disease Control and Prevention’s official recommendations still state that 7 to 8 hours is ideal for adults. Still, it may be time to stop stressing if you’re in the 6 to- 7 hour range; in fact, it may be good for you.

This story has been updated.