Raleigh, N.C. — New research from the Alzheimer's Association recently found that women who averaged too little or too much sleep each night had lower cognitive function than those who averaged about seven hours of sleep. 

Researchers studied 15,000 women over the age of 70 to look at sleep patterns and cognitive abilities. 

"On the short end, women were sleeping five or less hours and on the long end women were sleeping nine or more hours," said Dr. Elizabeth Devore, who authored the study.

Memory tests for women in the six-year study found too little or too much sleep was cognitively the same as aging a year and a half. With about 16 million Americans expected to have Alzheimer's by 2050, the findings could have big implications. 

"We may need to start looking in the future at sleep and circadian-based strategies for potentially reducing cognitive impairment and Alzheimer's disease," Devore said. 

The study also found that sleep becomes less consistent as people age, with older people sleeping less overall and experiencing more fragmented times of rest due to napping. Research points to the seven-hour mark as a goal for sleep. 

Big changes in sleep patterns could also be a concern, as women who changed at least two hours per day from the beginning of the study to the end performed worse on cognitive tests than those who saw no change in their sleep duration.