Impacts of Overweight and Obesity in Older Age on the Risk of Dementia: A Systematic Literature Review and a Meta-Analysis

Abstract

Background: It is unclear whether overweight and obesity in older age reduces or increases the risk of incident dementia. Objective: To assess the impacts of overweight and obesity in older age on incident dementia. Methods: We searched cohort studies reporting body weight measured in older age and dementia through PubMed, Embase, Medline, PyschInfo, and Cochrane library until July 2016. Sixteen articles were identified for the review. We pooled data from them and a new unpublished study from China, to calculate relative risk (RR) of incident dementia in relation to body mass index (BMI) and waist circumference (WC). Results: All 16 cohort studies were undertaken in high income countries, with follow-up periods ranging between 3 to 18 years. Thirteen studies showed an inverse association between BMI and dementia, and three studies demonstrated a positive association. Pooled RR of dementia in relation to continuous BMI from 14 studied populations, including the new Chinese data, was 0.97 (95% CI 0.95–1.00); in those followed up <9 years it was 0.95 (0.93–0.96) while in ≥9 years follow-up it was 1.03 (0.96–1.11). In five studied populations examining categorical BMI, RR of dementia in older people classified as overweight and obese was 0.98 (0.54–1.77) and 1.17 (0.65–2.10) respectively, in comparison with other weights. The pooled WC data showed no association between increased WC and reduced risk of dementia. Conclusion: The current evidence did not support a paradox on beneficial impacts of overweight and obesity in older age on incident dementia. More studies with long term follow up are needed to clarify the association of body weight in older age with dementia risk.

Age-dependent effects of body mass index across the adult life span on the risk of dementia: a cohort study with a genetic approach

“…BMI is associated with dementia, but research indicates that the relationship differs depending on the age when BMI is measured [2]. While a high BMI in midlife has been associated with increased risk of dementia in most studies, a high BMI in late-life may in fact be associated with a decreased risk of dementia-this is known as the "obesity paradox" [3].…”

“…While a high BMI in midlife has been associated with increased risk of dementia in most studies, a high BMI in late-life may in fact be associated with a decreased risk of dementia-this is known as the "obesity paradox" [3]. One hypothesis regarding the nature of this paradox is that unintentional weight loss in late-life may be an early sign in the prodromal stage of dementia [2].…”

Using Cross-Cultural Studies to Improve Evidence on Dementia Prevention: Lessons from the Special Issue Sponsored by the International Research Network on Dementia Prevention (IRNDP)

“…These points are well illustrated in the interesting array of studies in this issue of the journal. Danat et al [11] present a meta-analysis of studies evaluating the association between BMI and BMI categories with dementia risk, focusing on community-based studies that assessed BMI among people ages 65+. In this fascinating report, they find that among studies with less than 9 years of follow-up, the overall metaanalyzed relative risk per BMI point is 0.95 (95% CI: 0.93, 0.96), with a non-significant I 2 statistic of 21% (p = 0.25), indicating most of the heterogeneity between studies could be attributed to sampling variability.…”

“…These modifiers may relate to age of the sample, duration of the follow-up or contextual factors such that BMI represents distinct physiologic or social risk. Danat et al [11] highlight the potential for reverse causation: it is very likely that changes in BMI in late life are primarily consequences of disease, rather than determinants, and therefore not useful targets for preventive intervention. A key role for meta-research such as the Danat paper is to identify research gaps.…”

Dementia, Risk, Risk Reduction, and Translation into Practice: An International Research Network for Dementia Prevention (IRNDP) Special Issue

“…The articles on the risk factors associated with dementia range from analyses of new and established observational cohort studies [1][2][3] to systematic reviews [4,5]. And from factors more recently linked to dementia risk, including poor kidney function, chronic obstructive pulmonary disease, and air pollution [2,5,6] to the more established, obesity, social isolation, vascular and lifestyle factors such as diabetes or smoking [1,4,7]. We report protocols for two of the many ongoing trials in dementia risk reduction, the Systematic Multi-Domain Alzheimer's Risk Reduction Trial (SMARRT) [8] and the Maintain Your Brain trial [9], important adherence data from the Australian Imaging Biomarkers and Lifestyle (AIBL) active-study [10], an evaluation of an online health education tool for older adults in Malaysia [11], and some early work in mice [12].…”