The findings point to a growing awareness that sleep apnea contributes to a wide range of public health problems. All of the studies were reported at this week's annual meeting of the American Thoracic Society in San Francisco.
Obstructive sleep apnea is caused by a narrowing or collapse of throat tissues during sleep. Blood-oxygen levels plummet, and the body responds by sending out a flood of hormonal emergency signals. The sufferer wakes, sometimes 30 or more times an hour, his or her body in full "flight or fight" mode.
"That does a number on your sympathetic nervous system," Yale researcher Nader Botros, MD, MPH, tells WebMD. "It is as if you were waked at night because a saber-toothed tiger was chasing you."
This obviously prevents a good night's sleep and results in daytime sleepiness. But it also means that repeated stress signals take their toll. The new studies assess that toll.
Sleep Apnea and Car Crashes
Raw data suggest that sleep apnea raises the risk that a person will be involved in a motor vehicle accident. New data not only confirm this finding, but show that sleep apnea patients are at very high risk of serious, life-threatening car wrecks.
Alan Mulgrew, MD, and colleagues at the University of British Columbia in Vancouver compared the claims and accident records of 800 patients with confirmed sleep apnea with those of 800 people who did not have sleep apnea.
Over the three years before their diagnosis, the sleep apnea patients were nearly five times more likely to have serious car crashes than were other drivers. Serious car crashes were defined as those with injury or head-on crashes.
Many things contribute to driving risk. So Mulgrew's team carefully adjusted for things such as caffeine and alcohol consumption and shift work.
"No matter what you try to account for, sleep apnea patients still have these serious crashes in threefold excess," Mulgrew tells WebMD. "When we looked at the small number of truly awful crashes -- head-on collisions and collisions with pedestrians or cyclists -- 80% of the crashes of that kind were in sleep apnea patients."
All sleep apnea patients appeared to be at risk of crashing their cars. The problem wasn't limited to those with severe apnea.
"It didn't matter how severe your sleep apnea was. We found that you still have the same increased risk even if you have mild sleep apnea," Mulgrew says.
And patients seemed unable to tell when they were at greater risk. Patients who said they drove even when they felt sleepy were no more likely than other sleep apnea patients to wreck their cars.
The results of the study were so striking that Mulgrew now carefully asks his sleep apnea patients about their driving histories and about any "near misses" they might be having. He is much more likely to recommend the most effective sleep apnea treatment -- a continuous positive air pressure or CPAP device -- to patients with driving problems, even if their sleep apnea is relatively mild.
Sleep Apnea and Diabetes
To see whether the two conditions were related, the researchers kept track of nearly 600 sleep apnea patients for up to six years. Compared with similar men without sleep apnea, the patients were more than two-and-a-half times more likely to develop diabetes.
The more severe the sleep apnea, the higher the patients' risk of diabetes.
"We know that by measuring markers in the blood that the body of a person with sleep apnea is in a highly inflammatory, highly excitatory state," Botros says. "This state increases stress hormones, and we think the insulin-making pancreatic beta cells are affected."
Botros and colleagues are now looking at whether CPAP treatment can reduce sleep apnea patients' diabetes risk.
Sleep Apnea and Pregnancy Complications
Sleep apnea is more common among obese people. But the extra weight gain during the third trimester of pregnancy often puts a woman at risk of sleep apnea, says Hatim Youssef, DO, of the University of Medicine & Dentistry of New Jersey-Robert Wood Johnson Medical School.
Youssef and colleagues noticed that in their hospital, women tended to have low blood oxygen levels at night if their BMI (body mass index, a measure of weight according to height) went over 35. A BMI of 30 is considered obese for people who are not pregnant.
So the researchers analyzed the 2003 medical records of 4 million U.S. women who delivered babies. Only 452 of these 4 million women had sleep apnea. But these 452 women were much more likely than other women to experience complications:
- Women with sleep apnea were twice as likely as other women to have gestational diabetes.
- Women with sleep apnea were four times more likely than other women to have pregnancy-induced high blood pressure.
"I absolutely think women whose BMI goes over 35 when they are pregnant should be assessed for sleep apnea," Youssef tells WebMD. "We really are pushing our obstetric colleagues to have this on their radar because sleep apnea is very treatable. It may help to treat this condition, which is dangerous to the mother and to the fetus."
Sleep Apnea and Heart Attack, Heart Death
Having sleep apnea for four or five years raises a person's risk of having a heart attack or dying by 30%, find Neomi Shah, MD, and colleagues at Yale University.
Shah's team followed 1,123 patients evaluated for sleep apnea. More than 500 of these patients had 15 or more low-oxygen events per hour of sleep.
After adjusting for other heart risk factors, these patients were 30% more likely to have a heart attack or die over a four-and-a-half year period. The more severe the sleep apnea, the higher the risk of heart attack or death.
"There is some evidence to make us believe that when sleep apnea is appropriately treated, the risk of heart disease can be lowered," Shah says in a news release.