For teens with non-alcoholic fatty liver disease (NAFLD), breathing disruptions during sleep may worsen scarring in the liver, according to a new study.

Researchers found that among obese adolescents with NAFLD, those with the most severe liver disease also had the most severe sleep disordered breathing that caused them to experience periods of low oxygen at night.

"This really focuses on the role of oxidative stress both systemically and specifically in the liver as a driving factor of fibrosis and liver disease getting worse," said lead investigator Dr. Shikha Sundaram of the Children's Hospital Colorado and the University of Colorado School of Medicine.

Sleep apnea also increases the risk of cardiovascular disease, putting extra pressure on the heart to get oxygenated blood to the body, Sundaram told Reuters Health.

"Now we know that it also impacts the liver," as periods of normal oxygen levels and low oxygen levels repeat during sleep and increase scar tissue, though the mechanism is not yet completely understood, she said.

About seven million children in the U.S. have NAFLD, which can cause scarring in the liver and can lead to liver failure and the need for a transplant. NAFLD is also a major risk factor for type 2 diabetes. The condition may be related to genetics, obesity and some medications, and it can be treated but not cured.

Obstructive sleep apnea, when a sleeper's airway collapses and breathing stops then restarts abruptly, is common with obesity. The repeated interruptions in breathing throughout the night cause low blood oxygen levels, known as hypoxia, and have been linked to heart disease and stroke.

Past research has also tied sleep apnea to worsening NAFLD in adults, the study team notes in Journal of Hepatology. To see if this is true for teens, the researchers compared 36 obese teens with NAFLD, all around age 13, who underwent sleep studies, liver testing and urine analysis.

Of the 36 teens with NAFLD, 25 had sleep apnea or periods of hypoxia, during sleep.

Teens with obstructive sleep apnea/hypoxia had more severe liver fibrosis - scar tissue - than others, and had higher markers of oxidative stress, which is associated with worsening NAFLD, the researchers write.

The 23 teens with definite nonalcoholic steatohepatitis (NASH), a more severe form of liver disease that carries the highest risk for cirrhosis, end stage liver disease and liver cancer, had greater oxidative stress at night than those without NASH.

This and other recent studies indicate that liver disease and sleep apnea are closely related, Sundaram said. Both are related to obesity.

"I think that this and our previous work really is suggesting that if you have one or the other disease, talk to your physician, there is a possibility that you have the other disease," she said.

Untreated, sleep apnea can make fatty liver disease worse, she said.

If your child has NAFLD, ask your provider about the possibility of sleep apnea screening, she added.

Future trials should explore whether treating sleep apnea with a continuous positive airway pressure (CPAP) machine may affect NAFLD progression for teens, according to Maurizio Parola of the University of Torino Italy and Dr. Pietro Vajro of the University of Salerno in Italy, who coauthored an editorial on the findings.