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Declining dementia: Role of education, stroke prevalence

Tristan Manalac
10 Aug 2017
Study finds adults who adhered to the ‘5 A Day’ diet were found to be at a much lower risk of dementia after six years.

The prevalence of dementia, particularly vascular dementia and mild dementia, declined substantially between 1986 to 1987 and 2008 to 2010, a new study has found.

“The decline was mainly explained by the higher proportion with more than basic education and the lower odds ratio for dementia in those with stroke in the later born birth cohort,” said researchers.

The study involved two cohorts of 85-year-olds: those born in 1901 to 1902 and were examined in 1986 to 1987 (n=494; mean age 85.55±0.12 years; 71.1 percent female) and those born in 1923 to 1924 and were examined in 2008 to 2010 (n=571; mean age 85.91±0.17 years; 62.9 percent female).

Dementia diagnoses were classified as Alzheimer’s disease, vascular dementia or mixed dementia based on aetiology. Logistic regression models were used to determine relationship between birth cohort, sex, education and stroke on the prevalence of dementia.

The prevalence of dementia was significantly lower in the 2008 to 2010 cohort than in the 1986 to 1887 cohort (21.7 vs 29.8 percent; odds ratio [OR], 0.66; 95 percent CI, 0.50 to 0.86; p=0.003) regardless of method of diagnosis. [Sci Rep 2017;7:6136]

The trends were similar when dementia was diagnosed using either MMSE scores (OR, 0.72; 0.54 to 0.96) or examinations only (OR, 0.69; 0.52 to 0.91). Mild dementia decreased significantly from the 1986 to 1987 cohort (8.3 percent) to the 2008 to 2010 cohort (2.3 percent; p<0.01).

Logistic regression showed that education (OR, 0.70; 0.51 to 0.96), prevalent stroke (OR, 3.78; 2.28 to 6.29; p<0.001) and the interaction of stroke and birth cohort (OR, 0.50; 0.26 to 0.97; p=0.04) were significantly associated with the prevalence of dementia after adjusting for sex, education, stroke and other potential confounders.

In contrast, birth cohort alone (OR, 0.98; 068 to 1.41; p=0.920) and marital status (OR, 1.09; 0.76 to 1.57; p=0.628) were not.

According to the researchers, the current findings of decreasing dementia prevalence corroborate what is also increasingly being reported by other research groups.

“Recent epidemiological studies in several countries (UK, USA and Sweden included) have revealed a decrease in the incidence of age-standardized rates of dementia (i.e. the expected tsunami of dementia in ageing populations may be less problematic than predicted),” said Dr Barry Halliwell, chairman of the Biomedical Research Council at the Agency for Science Technology and Research (A*STAR) in Singapore.

“Note that the decrease is observed in the West. We don’t know if this is true for Asian countries such as Singapore and China,” noted Dr Feng Lei, a research assistant professor at the Department of Physiological Medicine in the Yong Loo Lin School of Medicine in Singapore.

While both doctors agreed to the roles that stroke and education play in dementia, they also highlighted the importance of taking other factors into consideration. “[M]any other factors play important roles, for example: diet, social engagement, physical activities, etc,” said Dr Lei.

“Education is indeed a powerful protective factor, as beautifully illustrated in the Nun study and many subsequent ones, but I would be surprised if changes in other risk factors did not contribute to the decrease observed [in the present study],” added Dr Halliwell. [Oncotarget 2015; 6:14082-14091; Curr Alzheimer Res 2012:9:6]

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