Abstract
As common risk factors of dementia, nine factors (low education, hearing loss, obesity, hypertension, smoking, depression, physical inactivity, diabetes and social isolation) were proposed. However, the joint impact of these factors on incident dementia is still uncertain; hence, we aimed to examine this impact. We conducted a cohort study of 9017 cognitively intact individuals aged≥65years in the Swedish Twin Registry. The main exposure was the total number of reported risk factors (ranging from 0 to 9). Data on dementia diagnoses were based on clinical workup and national health registers. After estimating the adjusted hazard ratios of incident dementia, the population attributable fraction (PAF) was calculated. We then conducted additional analyses, including APOE ε4 status in a genotyped subsample (n=2810) to check the relative impact of the main exposure and discordant twin pair (n=1158) analysis to consider confounding by familial effects (shared genetic or familial environmental factors). The number of dementia cases was 1950 (21.6%). A dose-response relationship between the number of risk factors and incident dementia was observed; hazard ratio (95% confidence interval) per one-unit increment in number of risk factors was 1.07 (1.03 to 1.11). The PAF for the combination of the nine risk factors was 10.4%. The PAF of all nine risk factors was smaller than that of APOE ε4 genotype (20.8%) in the subsample. Discordant pair analysis suggested that the observed association was notlikely explained by familial effects. The nine risk factors may have considerable impact as modifiable factors on incident dementia.
Highlights
As common risk factors of dementia, nine factors were proposed
Discordant pair analysis suggested that the observed association was not likely explained by familial effects
Ecological observations have suggested a decline in age-specific dementia incidence in several Western countries, and this population-level decrease may be explained by changes in educational level or lifestyles [3,4]
Summary
As common risk factors of dementia, nine factors (low education, hearing loss, obesity, hypertension, smoking, depression, physical inactivity, diabetes and social isolation) were proposed. Dementia is a worldwide public health problem, rapidly growing with population ageing [1]. In 2015, dementia affected 50 million people worldwide (about 5% of the world’s older population aged ≥ 60 years), and it is estimated that the number will be 82 million by 2030 and 152 million in 2050 [2]. Current medical treatments have only limited efficacy for treating dementia, and it is important to clarify strategies aimed at primary prevention. Ecological observations have suggested a decline in age-specific dementia incidence in several Western countries, and this population-level decrease may be explained by changes in educational level or lifestyles [3,4]. It was suggested that dementia is preventable by targeting modifiable risk factors. It is important to establish the impact of modifiable risk factors on incident dementia
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