Sleep apnea may increase the risk of developing gout and experiencing flare-ups, according to a new study.
The intense pain and swelling of a joint, often a big toe, that marks gout is caused by the deposition of uric acid crystals in joints and tissues.
Sleep apnea, the study team notes, causes periods of oxygen deprivation during the night when people stop breathing, which triggers overproduction of uric acid in the bloodstream.
But little was known about the relationship between the two conditions, the study team writes in Arthritis and Rheumatology.
In 2007-2008, almost six per cent of men and two per cent of women in the US experienced gout, according to the Centres for Disease Control and Prevention.
Sleep apnea, which is much more common, can increase the risk of high blood pressure, heart attack, stroke and heart failure, among other conditions, if untreated.
Obesity plays an important role in both sleep apnea and gout, but sleep apnea still increased the risk for gout even when weight was accounted for, said lead author Yuqing Zhang of Boston University Clinical Epidemiology Research and Training Unit.
The researchers used on almost 10,000 people with a new diagnosis of sleep apnea from a UK database and compared them to more than 40,000 people of similar sex, age, birth year and body composition but without sleep apnea.
Over a one-year period, there were 270 cases of gout, 76 in the sleep apnea group and 194 in the larger comparison group. Gout was diagnosed at an average age of 60.
Gout was almost twice as common in the sleep apnea group as in the comparison group, according to the analysis.
"When people have a gout attack it's so painful, they have limited mobility, they cannot put even one piece of paper on the toe," Zhang told Reuters Health.
Although obesity increases the risk for sleep apnea, some thin people have sleep apnea, too, and even in these people the risk of gout was increased by 80 per cent, he said.
The next step is to test whether treating sleep apnea also reduces the risk for gout, which seems likely, he said.
"Some studies show that if you get treatment, your uric acid may go down," Zhang said.
Sleep apnea can be treated with lifestyle changes, such as losing weight or wearing mouthpieces or breathing devices at night, or with surgery.
It takes years for uric acid crystals to accumulate in the joints and lead to an eventual gout flare, so sleep apnea may not "cause" the gout, but may create a more ideal environment for a flare up, said Dr. Robert Thomas Keenan of Duke University School of Medicine in Durham, North Carolina, who was not part of the new study.
"Gout is the most common inflammatory arthritis in the western world," he told Reuters Health by email.
"Sleep apnea and gout risks can be reduced in many people by losing weight if they are overweight, eating healthy and indulging in alcohol and red meats in moderation," he said.