A common breathing disorder called sleep apnea, in which sleepers stop breathing hundreds of times during the night, has been linked to memory decline and dementia. The findings are important because sleep apnea may affect more than half of seniors but is a treatable condition.
In addition to causing daytime sleepiness and fatigue, sleep apnea has been linked to medical conditions like heart disease, high blood pressure and diabetes. Poor sleep and sleep apnea have also been linked to forgetfulness and memory problems. But this is the first study to document sleep apnea using medical monitoring and to study its effects on the brain and cognition over time.
Sleep apnea is common in older people, especially men and those who are overweight. It occurs when the soft tissues at the back of the mouth and throat relax too much during sleep, causing the airways to become blocked. People with the condition often snore loudly and can wake up hundreds of times during the night, leading to daytime grogginess and fuzzy thinking, though they typically do not remember waking during the night.
This study, published in the Journal of the American Medical Association, looked at elderly women and also found a high rate of sleep-disordered breathing. The researchers, from the University of California, San Francisco, followed 298 elderly women whose average age was 82. They were healthy women living in communities in and around Baltimore, Md.; Minneapolis; Portland, Ore.; and Pittsburgh.
None of the women had memory problems at the start of the study. All were monitored using special home equipment that recorded their breathing during sleep. About a third of the women, or 105, were found to have 15 or more episodes of breathing problems per hour of sleep. They were also given tests of memory function.
By the end of the study, about five years later, more than a third of the women had developed serious memory problems. Almost 16 percent had developed the serious memory and thinking problems of dementia. Another 20 percent had mild cognitive impairment, which sometimes precedes dementia.
Women who had breathing problems during sleep were more likely to have memory problems. More than 44 percent of the women with sleep apnea had dementia or mild cognitive impairment, compared to 31 percent of the women who did not have sleep-disordered breathing. The researchers controlled for factors like age, weight, educational level, smoking, medication use and medical conditions, and still the association between breathing problems during sleep and dementia persisted.
One reason why sleep apnea may cause memory problems is that the condition is associated with low blood oxygen levels, which would reduce oxygen supply to the brain. The researchers found that those who had low oxygen levels during sleep were more likely to develop dementia. Waking up many times during the night and total sleep time, on the other hand, were not linked to dementia.
"Given the high prevalence of both sleep-disordered breathing and cognitive impairment among older adults, the possibility of an association between the two conditions, even a modest one, has the potential for a large public health impact," the authors wrote.
The authors note that the increased risk for memory and thinking problems associated with sleep-disordered breathing opens a new avenue for additional research on the risk for the development of memory problems. Additional studies involving more people, including men, will be needed to help determine the effects of sleep problems on Alzheimer's disease and other forms of dementia. Most of the women in the current study were white, so additional studies of other ethnicities would also be useful, the authors note.
Sleep apnea may be particularly prevalent in people with Alzheimer’s disease, with some estimates as high as 70 to 80 percent. Earlier research has shown that elderly patients with Alzheimer's disease suffered more severe symptoms from sleep apnea, including frequent awakenings, than sleep apnea patients without dementia.
The most effective treatment for the condition is to wear a special mask over the face and nose during sleep that delivers a steady stream of air. The treatment, known as CPAP, for continuous positive airway pressure, can be cumbersome, but it is effective for relieving symptoms.
If you suspect that breathing problems during sleep may be contributing to memory and thinking problems, it is important to discuss this with your doctor.
Source: Kristine Yaffe; Alison M. Laffan; Stephanie Litwack Harrison, et al: "Sleep-Disordered Breathing, Hypoxia, and Risk of Mild Cognitive Impairment and Dementia in Older Women." Journal of the American Medical Association, Vol. 306, pages 613-619.