Less than 6 hours of sleep could double death risk for those with metabolic syndrome

A new study from the American Heart Association finds sleeping less than six hours a night could more than double the risk of death for people with metabolic syndrome, which impacts more than a third of the U.S. adult population. Metabolic syndrome includes risk factors for heart disease, diabetes and stroke.

"There's a lot of hypotheses as to why this might be. We know that lack of sleep can change brain areas like the hypothalamus and hormone secretion to potentially increase appetite. [It] can turn on your sympathetic nervous system, the 'fight or flight,' which could raise your blood pressure," Dr. Tara Narula, a cardiologist at Northwell Health, said Thursday on "CBS This Morning." "It can change hormones secretion like growth hormone and cortisol, your stress hormone, that could cause imbalances in your glucose metabolism and regulation."

In order to be diagnosed with metabolic syndrome, Narula said you need to have at least three of these symptoms: "Elevated or enlarged waist circumference, low HDL ['good' cholesterol], high triglycerides, high blood pressure and high fasting blood sugar."

The study also broke new ground by measuring people's sleep in a laboratory setting, Narula said, versus the more common self-reported sleep studies. It also factored out sleep disorders like sleep apnea, which raises cardiovascular risk, she said.

"In this study they kind of took that out of the equation and really focused on just the duration of the sleep," Narula said, but she added that it only studied one night per person.

Seven to eight hours of sleep are recommended for adults each night, not including naps, Narula said.

Even without the risk factors, Narula said everyone needs to practice good sleep hygiene.

"We need to make it a priority," she said.