More data from the long-running Mayo Clinic Study of Aging has revealed that, in this one part of the U.S. at least, MCI develops at an overall rate of 6.4% a year among older adults (70+), with a higher rate for men and the less-educated.
The study involved 1,450 older adults (aged 70-89), who underwent memory testing every 15 months for an average of three years. By the end of the study period, 296 people had developed MCI, a rate of 6.4% per year. For men, the rate was 7.2% compared to 5.7% for women.
It should be noted that these rates apply to a relatively homogeneous group of people. Participants come from one county in Minnesota, an overwhelmingly white part of the U.S.
MCI comes in two types: amnestic (involving memory loss) and non-amnestic. Amnestic MCI was more than twice as common as non-amnestic MCI. The incidence rate of aMCI was also higher for men (4.4%) than women (3.3%), as was the risk of naMCI (2% vs 1.1%).
Those who had less education also had higher rates of MCI. For aMCI, the rate for those with 12 years or less of education was 4.3%, compared to 3.25% for those with more education. Similarly, for naMCI, the rates were 2% and 1%, respectively.
While the great majority of people diagnosed with MCI continued to have the disorder or progressed to dementia, some 12% were later re-diagnosed as not having it. This, I would presume, probably reflects temporary ‘dips’ in cognitive performance as a consequence of physical or emotional problems.
The differences between aMCI and naMCI, and between genders, suggest that risk factors for these should be considered separately.
 . The incidence of MCI differs by subtype and is higher in men. Neurology [Internet]. 2012 ;78(5):342 - 351. Available from: http://www.neurology.org/content/78/5/342.abstract?sid=ddadf8f9-f2c0-4705-8d9e-b538531fea57