Association of obesity and dementia varies with age

1. Younger patients hospitalized with a first-time diagnosis of obesity had a higher risk of subsequent hospitalization with dementia, while older patients hospitalized with obesity had a lower risk of subsequent hospitalization with dementia. 

2. The increased risk of hospitalization with dementia seen in younger people may be specific to vascular causes of dementia. 

Evidence Rating Level: 2 (Good) 

Study Rundown: There is increasing evidence that obesity is a risk factor for the development of dementia. Past studies have evaluated the risk at different ages and have suggested an age dependent relationship. This study found that people hospitalized at a young age with a first-time diagnosis of obesity had a higher risk of subsequent hospital admission with a diagnosis of dementia. The highest risk was found in the youngest studied individuals, at age 30-39 years. With increasing age of hospitalization with obesity, there remained an elevated but decreasing risk of subsequent hospitalization with dementia, until age 70-79, at which point there was neither an increased nor decreased risk of subsequent hospitalization with dementia. At age ≥80, hospitalization with a first-time diagnosis of obesity was associated with a decreased risk of subsequent hospitalization with dementia.

The large sample size is a strength of this study. Furthermore, the Hospital Episodes Statistics dataset, from which the raw data was extracted, contains information about all hospital admissions in the National Health Service. Limitations of this study include a relatively short duration of follow-up (14 years), as individuals may not fully manifest dementia as a chronically progressive disease within this time frame. Further, the inclusion criteria of hospitalization with a primary or secondary diagnosis of obesity does not account for individuals who were obese years before hospitalization, or for confounding primary diagnoses that may also be related to dementia. Nevertheless, these data do provide additional evidence that obesity is related to the development of dementia, and suggest that obesity at a younger age increases one’s risk of subsequent dementia.

Click to read the study, published today in the BMJ Postgraduate Medical Journal

Relevant Reading: Obesity and central obesity as risk factors for incident dementia and its subtypes

In-Depth [retrospective cohort]: This study evaluated the risk of hospital admission with a diagnosis of dementia in individuals who had previously had a hospital admission with a first-time diagnosis of obesity. 451,232 men and women in the United Kingdom age ≥30 hospitalized with a first-time primary or secondary diagnosis of obesity. The rate of subsequent admission with a diagnosis of dementia was compared to the rate of subsequent admission for dementia in a control cohort of individuals originally hospitalized with minor medical or surgical conditions. Risk ratios were calculated to determine risk of subsequent admission with dementia in the exposure (obesity admission) group. The comparisons were stratified then standardized by age, sex, calendar year of first recorded admission, and socioeconomic status indicators.

The risk ratio (RR) for people aged 30-39 years hospitalized with a first record of obesity was 3.5 (CI95% 2.1-5.6), and reduced with increasing age at obesity: from age 40-49, the RR for subsequent admission with dementia was 1.7 (CI95% 1.3-2.2); from age 50-59, RR 1.5 (CI95% 1.3-1.7); from age 60-69, RR 1.4 (CI95% 1.3-1.5). In individuals aged 70-79 years, there was neither an increased nor decreased risk of subsequent admission with dementia. In people aged ≥80 at first admission with obesity, the RR of subsequent admission with dementia was 0.78 (CI95% 0.74-0.82), suggesting a protective effect of obesity in older age. In the analysis divided by dementia type – Alzheimer’s versus vascular – the results suggest higher risk of subsequent dementia in younger individuals with obesity may be primarily in those individuals who develop vascular dementia. The transition from higher to lower risk of dementia associated with obesity occurred at an earlier age in people who developed Alzheimer’s disease, compared to those who developed vascular dementia.

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