TUESDAY, Dec. 13, 2011 (HealthDay News) -- An older woman's sleep/wake cycle and levels of physical activity may affect her risk of developing dementia, a new study suggests.
It found that the risk of dementia or "mild cognitive impairment" (a state that sometimes precedes dementia) was higher in older women with weaker circadian rhythms who are either less physically active or more active later in the day, compared to those who have a stronger circadian rhythm and are more active earlier in the day.
"We've known for some time that circadian rhythms, what people often refer to as the 'body clock,' can have an impact on our brain and our ability to function normally," lead author Greg Tranah, a scientist at the California Pacific Medical Center Research Institute, said in an institute news release.
"What our findings suggest is that future interventions such as increased physical activity or using light exposure interventions to influence circadian rhythms, could help influence cognitive [mental] outcomes in older women," he explained.
Tranah and colleagues analyzed data from almost 1,300 healthy women, over age 75, who were followed for five years. At the end of that time, 15 percent of the women had developed dementia and 24 percent had some form of mild cognitive impairment (MCI).
Women with weaker circadian rhythms who had lower levels of physical activity or who were most active later in the day were 80 percent more likely to develop dementia or MCI than those with stronger circadian rhythms who were active earlier in the day, the team found.
"To our knowledge this is the first study to show such a strong connection between circadian activity rhythm and the subsequent development of dementia or MCI," Tranah said. The finding marks an association only, however, and cannot prove cause-and-effect.
"The reasons why this is so are not yet clear," he added. "The changes in circadian rhythm may directly influence the onset of dementia or MCI, or the decrease in activity may be a consequence, a warning sign if you like, that changes are already taking place in the brain. Identifying what the reason is could help us develop therapies to delay, or slow down, the development of brain problems in the elderly."
The study was published online Dec. 7 in Annals of Neurology.
The American Academy of Family Physicians has more about dementia.