Sleep apnea linked to increased risk of dementia in elderly women: Page 2 of 3

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October 3, 2011

These women, 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 four years later, sleep specialists came to the study subjects' homes and monitored the women as they slept using specialized 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 (the complete blockage or airflow) or hypopneas (a reduction of airflow of 30 percent or more) and how much time they spent in an oxygen-deprived state.

About five years after their 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. The tests included the Mini-Mental State Examination, the California Learning Verbal Test and a test of executive function called Trails B.

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.

When Yaffe and her colleagues tabulated the results of the study, they found that about one third (35.2 percent) of all the women developed dementia or mild cognitive impairment. They also found 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 percent of them developed dementia or mild cognitive impairment, compared with 31.1 percent of those who didn't have impaired breathing and sleep.

The findings suggest that the key factor leading to diminished cognition was oxygen deprivation, also called 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.