The authors of the study were Dr Deborah Barnes, an associate professor of psychiatry at UCSF, and a mental health researcher at the San Francisco VA Medical Center, and Dr Kristine Yaffe, professor of psychiatry, neurology and epidemiology at UCSF. You can read how they analyzed data from studies around the world involving hundreds of thousands of participants and arrived at these findings in the 19 July early online issue of The Lancet Neurology.
There are currently about 33.9 million people worldwide with Alzheimer's Disease, with three times this number expected by 2050.
Barnes and Yaffe investigated the available evidence on seven potentially modifiable risk factors for Alzheimer's Disease. They projected how reduction in these factors might affect the prevalence of the disease by calculating the percentage of cases tied to a given factor, and the number of cases that might be prevented if each factor were reduced by 10% and 25%, both worldwide and in the US.
The seven modifiable risk factors that they investigated were: diabetes, high blood pressure in mid-life, obesity in mid-life, smoking, depression, low educational attainment or cognitive inactivity, and physical inactivity.
They found that:
- Up to just over half of worldwide (17.2 million) and US (2.9 million) cases of Alzheimer's Disease are potentially attributable to these seven modifiable risk factors
- Reducing all seven risk factors by 10% to 25% could potentially prevent as many as 1.1 to 3.0 million cases worldwide, and between 184,000 and 492,000 cases in the US.
- In descending order of magnitude of impact worldwide, low education has the biggest impact, followed by smoking, physical inactivity, depression, mid-life hypertension, diabetes and mid-life obesity.
- For the US, physical inactivity has the biggest impact, followed by depression, smoking, mid-life hypertension, mid-life obesity, low education and diabetes.
"What's exciting is that this suggests that some very simple lifestyle changes, such as increasing physical activity and quitting smoking, could have a tremendous impact on preventing Alzheimer's and other dementias in the United States and worldwide."
However, she did warn we should be somewhat circumspect in our interpretation of the results, since she and her team have assumed that these factors actually cause Alzheimer's:
"We are assuming that when you change the risk factor, then you change the risk. What we need to do now is figure out whether that assumption is correct," she cautioned.
However, given the huge number of cases involved, and that it might not be unreasonable to assume some causative effect here, then many might be disposed to agree with Yaffe, who said:
"It would be extremely significant if we could find out how to prevent even some of those cases."
Funds from the Alzheimer's Association, the National Alliance for Research on Schizophrenia and Depression, the UCSF School of Medicine and the National Institute on Aging, helped pay for the study, which also featured recently at the 2011 meeting of the Alzheimer's Association International Conference on Alzheimer's Disease in Paris.
"The projected effect of risk factor reduction on Alzheimer's disease prevalence."
Deborah E Barnes, Kristine Yaffe.
The Lancet Neurology, Early Online Publication, 19 July 2011
Additional source: University of California San Francisco.
Written by: Catharine Paddock, PhD