Elderly women who suffer from sleep apnea, a condition characterized by disrupted breathing and sleep and a reduction in the intake of oxygen, are about twice as likely to develop dementia in the next five years as those without the condition.
published in the Journal of the American Medical Association
demonstrated for the first time that sleep apnea, also known as sleep-disordered breathing (SDB), can deprive the brain and other organs of the oxygen and may trigger declines in cognitive ability over a long-term period.
“This is the first study to show that sleep apnea may lead to cognitive impairment,” said lead author Kristine Yaffe, MD, of the University of California, San Francisco, in a statement
. “It suggests that there is a biological connection between sleep and cognition and also suggests that treatment of sleep apnea might help prevent or delay the onset of dementia in older adults.”
Although it can’t be definitively concluded that SDB causes cognitive impairment, the study results suggest that it may at least be a contributing factor, she noted.
In patients with sleep apnea, the airways leading from the lungs to the nose and mouth collapse during sleep, interfering with an individual’s ability to inhale. Although previous research had uncovered a link between sleep apnea and dementia, the studies weren’t structured to follow the impact of sleep apnea on individuals who had normal cognitive abilities at the onset. The strength of the new findings stems from the fact that the 298 subjects began the study without dementia or measurable cognitive impairments, allowing researchers to measure the relationship between sleep apnea and mental acuity.
The participants, who were drawn from a larger, ongoing study examining osteoporosis in more than 10,000 women over 65, were first examined at clinics in Pittsburgh and Minneapolis and given tests that assessed their mental and cognitive abilities. Those who were found to be suffering from dementia or mild cognitive impairment at the initial assessment weren’t included in the study.
About 4 years later, sleep specialists visited the study subjects’ homes and monitored them as they slept using equipment that measured brain activity, heart rhythm, leg movements, airflow, breathing activity in their chest and abdomen and the oxygen content of blood as it passed through their fingers. These instruments allowed researchers to track how often the women experienced apneas or hypopneas and how much time they spent in an oxygen-deprived state.
About 5 years after the initial first visit, the women returned to the clinics and were given a larger battery of tests that measured their cognitive abilities, memory, and verbal fluency. Women whose test results suggested they had dementia or mild cognitive impairment had their records reviewed by a panel of clinical experts who decided whether to confirm the diagnosis.
Dr. Yaffe and colleagues concluded that about one third (35.2%) of participants developed dementia or mild cognitive impairment, and that those with sleep apnea were almost twice as likely to become cognitively impaired.
Among the women found to suffer from sleep-disordered breathing, 44.8% developed dementia or mild cognitive impairment, compared with 31.1% of those who didn’t have impaired breathing and sleep.
The findings suggest that the key factor leading to diminished cognition was hypoxia. Women who had frequent episodes of low oxygen or spent a large portion of their sleep time in a state of hypoxia were more likely to develop cognitive impairment. By contrast, no independent connection was seen between dementia and the number of times patients were awakened in their struggle to breathe.
Providing oxygen therapy to elderly people with sleep apnea may reduce the chances of cognitively impairment or delay the onset of mental decline, the authors found.