Beginning in 1971, healthy older adults in Gothenburg, Sweden, have been participating in a longitudinal study of their cognitive health. The first H70 study started in 1971 with 381 residents of Gothenburg who were 70 years old; a new one began in 2000 with 551 residents and is still ongoing. For the first cohort (born in 1901-02), low scores on non-memory tests turned out to be a good predictor of dementia; however, these tests were not predictive for the generation born in 1930. Those from the later cohort also performed better in the intelligence tests at age 70 than their predecessors had.
It’s suggested that the higher intelligence is down to the later cohort’s better pre and postnatal care, better nutrition, higher quality education, and better treatment of high blood pressure and cholesterol. And possibly the cognitive demands of modern life.
Nevertheless, the researchers reported that the incidence of dementia at age 75 was little different (5% in the first cohort and 4.4% in the later). However, since a substantially greater proportion of the first cohort were dead by that age (15.7% compared to 4.4% of the 2nd cohort), it seems quite probable that there really was a higher incidence of dementia in the earlier cohort.
The fact that low scores on non-memory cognitive tests were predictive in the first cohort of both dementia and death by age 75 supports this argument.
The fact that low scores on non-memory cognitive tests were not predictive of dementia or death in the later cohort is in keeping with the evidence that higher levels of education help delay dementia. We will need to wait for later findings from this study to see whether that is what is happening.
The findings are not inconsistent with those from a very large U.S. national study that found older adults (70+) are now less likely to be cognitively impaired (see below). It was suggested then also that better healthcare and more education were factors behind this decline in the rate of cognitive impairment.
A new nationally representative study involving 11,000 people shows a downward trend in the rate of cognitive impairment among people aged 70 and older, from 12.2% to 8.7% between 1993 and 2002. It’s speculated that factors behind this decline may be that today’s older people are much likelier to have had more formal education, higher economic status, and better care for risk factors such as high blood pressure, high cholesterol and smoking that can jeopardize their brains. In fact the data suggest that about 40% of the decrease in cognitive impairment over the decade was likely due to the increase in education levels and personal wealth between the two groups of seniors studied at the two time points. The trend is consistent with a dramatic decline in chronic disability among older Americans over the past two decades.
 . Secular changes in cognitive predictors of dementia and mortality in 70-year-olds. Neurology [Internet]. 2010 ;75(9):779 - 785. Available from: http://www.neurology.org/content/75/9/779.abstract
 . Trends in the Prevalence and Mortality of Cognitive Impairment in the United States: Is There Evidence of a Compression of Cognitive Morbidity?. Alzheimer's & dementia : the journal of the Alzheimer's Association. 2008 ;4(2):134 - 144.