(dailyRx News) Dementia more often occurs in elderly women who are physically inactive, are active later in the day, or have abnormal sleep-wake schedules.
The group has an 80 percent higher chance of developing mild cognitive impairment (MCI) or dementia, says Greg Tranah, Ph.D., a scientist at the California Pacific Medical Center Research Institute in San Francisco. His team studied almost 1,300 women for five years.
Most people's body clock, the circadian rhythm, helps wake them up between 6 a.m. and 8 a.m. They go to bed between 10 p.m. and 12 a.m. Normal rhythms vary for Individuals, but they are fairly regular.
In Dr. Tranah's study, women were less likely to develop dementia or MCI if they had strong circadian rhythm activity or were most physically active between 1:34 p.m. - 3:51 p.m..
The researchers collected data on activity and circadian rhythm from healthy women, all older than 75 (mean age 83). None lived in a nursing home or other group facility. No one had cognitive impairment or dementia when the study started.
After five years,15 percent of the women had developed dementia. MCI occurred in 24 percent. At highest risk were women with weaker circadian rhythm activity, lower levels of activity, or whose peak activity occurred after 3:50 p.m.
“We’ve known for some time that circadian rhythms can have an impact on the brain and the ability to function normally,” Dr. Tranah says. "This is the first study to show such a strong connection between circadian rhythm and the subsequent development of dementia or MCI."
No one knows why circadian rhythm and mental status are linked. A decrease in one might cause the other, says Dr. Tranah.
He says new research should study whether dementia and MCI rates improve after elderly women increase physical activity or use light to influence circadian rhythms.
Dr. Tranah and his team published their observational study in the Annals of Neurology.