(CBS/AP) The rate of Alzheimer's disease and other dementias is falling in the United States and other wealthy countries -- a bit of good news about an epidemic that is still growing simply because more people are living to an old age, new studies show.
Researchers say this trend is likely due to improved education and better control of health factors such as cholesterol and blood pressure.
Studies in the Netherlands, Sweden, Germany and England suggest the number of people diagnosed with dementia has gone down there. However, the opposite is occurring in some poorer countries that have lagged on education and health, such as in sub-Saharan Africa, where dementia seems to be rising.
"The results bring some hope that perhaps dementia cases might be preventable, or at least delayed" by improving health and education, said the study leader, Claudia Satizabal of Boston University.
More than 5.4 million Americans and 35 million people worldwide have Alzheimer's, the most common form of dementia. The disease has no cure and current drugs only temporarily ease symptoms at best.
Dr. Kenneth Langa, an expert on aging from the University of Michigan, discussed the studies Tuesday at the Alzheimer's Association International Conference in Copenhagen.
In the U.S., the federally funded Framingham study tracked new dementia cases among several thousand people 60 and older in five-year periods starting in 1978, 1989, 1996 and 2006. Compared with the first period, new cases were 22 percent lower in the second one, 38 percent lower in the third and 44 percent lower in the fourth one.
The average age at which dementia was diagnosed also rose -- from 80 during the first period to 85 in the last one.
An American over age 60 today has a 44 percent lower chance of developing dementia than a similar-aged person did roughly 30 years ago, the longest study of these trends in the U.S. concluded.
Researchers found these rates also correlate with decline in smoking, heart disease and strokes, and a rise in the number of people using blood pressure medicines and getting a high school diploma.
But recent research has also shown dementia is taking the lives of many Americans and may kill at almost the same rate as heart disease.
Other wealthy countries also note a similar trend as the U.S. The German Center for Neurodegenerative Diseases says data from Germany's largest public health insurance company suggest that new cases of dementia declined significantly between 2007 and 2009 in men and women. The trends corresponded with fewer strokes and better treatment of high blood pressure, cholesterol and diabetes, and more education, they said.
In Colombia researchers believe the current projections might underestimate dementia cases by up to 50 percent, while estimates in studies from China and sub-Saharan Africa and the United Nations conclude that previous estimates for the disease worldwide were too low.
An updated study by Alzheimer's Disease International in 2009 says dementia prevalence appears to have increased from about 5 percent to about 7 percent in East Asia and between 2 percent and 4 percent to nearly 5 percent in Sub-Saharan Africa.