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

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 We pooled data from them and a new unpublished study from China, to calculate relative risk (RR) of incident dementia in relation to body mass index (BMI) and waist circumference (WC).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.

Association between fish consumption and risk of dementia: a new study from China and a systematic literature review and meta-analysis.

OBJECTIVE: To assess the association of fish consumption with risk of dementia and its dose-response relationship, and investigate variations in the association among low-, middle- and high-income countries. DESIGN: A new community-based cross-sectional study and a systematic literature review.SettingsUrban and rural communities in China; population-based studies systematically searched from worldwide literature. SUBJECTS: Chinese adults aged ≥60 years in six provinces (n 6981) took part in a household health survey of dementia prevalence and risk factors. In addition, 33 964 participants from eleven published and eligible studies were included in the systematic review and meta-analysis. RESULTS: In the new study in China, 326 participants were diagnosed with dementia (4·7 %); those who consumed any amount of fish in the past two years v. those who consumed no fish had reduced risk of dementia (adjusted OR=0·73, 95 % CI 0·64, 0·99), but the dose-response relationship was not statistically significant. The meta-analysis of available data from the literature and the new study showed relative risk (RR) of dementia of 0·80 (95 % CI 0·74, 0·87) for people with fish consumption; the impact was similar among countries with different levels of income. Pooled dose-response data revealed RR (95 % CI) of 0·84 (0·72, 0·98), 0·78 (0·68, 0·90) and 0·77 (0·61, 0·98) in people with low, middle and high consumption of fish, respectively. Corresponding figures for Alzheimer's disease were 0·88 (0·74, 1·04), 0·79 (0·65, 0·96) and 0·67 (0·58, 0·78), respectively. CONCLUSIONS: Greater consumption of fish is associated with a lower risk of dementia. Increasing fish consumption may help prevent dementia worldwide regardless of income level.

Prevalence and determinants of undetected dementia in the community: a systematic literature review and a meta-analysis.

OBJECTIVES: Detection of dementia is essential for improving the lives of patients but the extent of underdetection worldwide and its causes are not known. This study aimed to quantify the prevalence of undetected dementia and to examine its correlates. METHODS/SETTING/PARTICIPANTS: A systematic search was conducted until October 2016 for studies reporting the proportion of undetected dementia and/or its determinants in either the community or in residential care settings worldwide. Random-effects models calculated the pooled rate of undetected dementia and subgroup analyses were conducted to identify determinants of the variation. PRIMARY AND SECONDARY OUTCOME MEASURES: The outcome measures of interest were the prevalence and determinants of undetected dementia. RESULTS: 23 studies were eligible for inclusion in this review. The pooled rate of undetected dementia was 61.7% (95% CI 55.0% to 68.0%). The rate of underdetection was higher in China and India (vs Europe and North America), in the community setting (vs residential/nursing care), age of <70 years, male gender and diagnosis by general practitioner. However, it was lower in the studies using Mini-Mental State Examination (MMSE) diagnosis criteria. CONCLUSIONS: The prevalence of undetected dementia is high globally. Wide variations in detecting dementia need to be urgently examined, particularly in populations with low socioeconomic status. Efforts are required to reduce diagnostic inequality and to improve early diagnosis in the community.