Sleep apnea is a condition where the airways leading from the lungs to the nose and mouth collapse as the individuals sleep, interfering with the ability to inhale. Some previous research has suggested a link between sleep apnea and dementia. Kristine Yaffe, from University of California/San Francisco (UCSD; California, USA), and colleagues followed 298 women, average age 82.3 years, who were enrolled in a larger, ongoing study examining osteoporosis in more than 10,000 women over 65; the women began the study without dementia or measurable cognitive impairments, allowing researchers to measure the relationship between sleep apnea and mental acuity. 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% 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 the researchers tabulated the results of the study, they found that about one third (35.2%) 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% of them 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 oxygen deprivation, also called hypoxia. The team concludes that: “Among older women, those with sleep-disordered breathing compared with those without sleep-disordered breathing had an increased risk of developing cognitive impairment.”