Sleep Apnea Takes Another Victim: The Liver
The casualties of sleep apnea are many: high blood pressure, cardiovascular disease, stroke, diabetes, various psychological disorders... not to mention injuries from accidents due to lack of sleep. Now, researchers at the University of Bern in Switzerland have established a link between sleep apnea and liver disease.
Obstructive sleep apnea, which was only seriously studied as a disorder since the late 1960's, is estimated to occur in nine percent of middle aged women and 24 percent of middle aged men. It prevents oxygen from entering the bloodstream during sleep due to the muscles of the tongue and surrounding pharynx relaxing. In relaxing, they come together, closing off the airway - in effect, stopping breathing. While it is true that snoring is an indication of sleep apnea, not all persons who snore are deprived of oxygen in the way described for sleep apnea patients.
You may think that liver disease (steatohepatitis) is largely the result of drug or alcohol abuse, but 40 percent of the population with liver disease suffer from non-alcoholic liver disease, or NASH. Though NASH has few outward symptoms - thus, it is known as the "silent liver disease" - an ultrasound and liver biopsy would reveal fat and inflammation in the liver. This condition needs to be treated before the damage becomes irreversible (cirrhosis).
The Link Between Sleep Apnea And Liver Disease
The Bern research involved studies of normal mice kept in a low oxygen environment for seven days; the control group was kept in a normal oxygen environment. After seven days, the mice in the low oxygen atmosphere showed pronounced fat deposits and inflammation in the livers. These effects were not observed in the normal oxygen group.
Also observed were the genes of the low oxygen group. The genes responsible for fat synthesis were shown to be highly active, while the genes responsible for fat breakdown showed reduced activity.
The third observation of the low oxygen group was that the mice were less sensitive to insulin than the control group.
Dr Anne-Christine Piguet, head of the research team, concluded "Hypoxia (lack of oxygen) may be the link leading to accumulation of fat in the liver and to the progression of non-alcoholic steatohepatitis. Our findings show that it is important both to screen obese patients for obstructive sleep apnoea [British spelling] to prevent it contributing to fatty liver disease and to treat those patients who already have NASH for hypoxia which may be making their condition worse."
In this experiment we see sleep apnea as causal to NASH and possibly to diabetes. In human patients, it has been observed that obesity predisposes patients to fatty liver diseases and to obstructive sleep apnea. It remains for the lose ends to be tied up, but it looks like the team from Bern are onto something.