According to a Duke University study, population health scientists have described Alzheimer's disease as both decreasing and increasing in prevalence.
The confusion, it seems, stems from the difficulty in making a definitive diagnosis. Lack of standardization in identifying patients can cause different study results.
Igor Akushevich, associate research professor and member of the Biodemography of Aging Unit the Social Science Research Institute at Duke, noted in his research the confusion in decreasing and increasing numbers of Alzheimer's diagnoses.
"We found that although the prevalence of Alzheimer's disease diagnoses in the Medicare population is increasing, the level of cognitive impairment in these very same individuals has been going down. It likely suggests that doctors are identifying the disease at increasingly earlier stages," he said.
There are other factors that lead to the rise and fall of the prevalence of the disease. For instance, people are living longer with Alzheimer's because of better interventions. If more people survive other medical conditions, then more will live long enough to develop Alzheimer's.
There are more aggressive treatments for risks of heart disease and diabetes, both of which are associated with a higher risk for Alzheimer's. Protecting against one could protect against the other. Another factor is that more people reach higher levels of education now, which could directly affect brain development in a way that protects against Alzheimer's and dementia, according to the Population Reference Bureau.
Interestingly, the bureau also reported that while the prevalence of dementia can fall, the rate of Alzheimer's deaths rise. The older population is growing at a faster rate now than the younger population, and people are more likely to develop dementia in old age.
Even though the risk of developing dementia is dropping in each age group, the age groups more likely to get diagnosed with the impairment are growing in number at an unprecedented rate. And because of improved dementia diagnoses rates, better cause-of-death determinations and better dementia prognosis and treatment of other diseases, the number of people who die from complications from Alzheimer's disease is rising at the same time the older population is growing.