Is there an association between body mass index and cognitive function in older adults?

A recent study published in the Nutrients Journal examined whether changes in body mass index (BMI) were associated with the temporal change in cognitive performance in older adults.

Study: Longitudinal Examination of Body Mass Index and Cognitive Function in Older Adults: The HELIAD Study. Image Credit: SewCreamStudio/Shutterstock.com

Background

Cognitive decline and neurodegenerative diseases, including dementia and Alzheimer's disease, are growing concerns in the aging of the population.

Statistics indicate that more than 55 million people worldwide have dementia, and the number of cases is expected to be more than twice that by 2050.

With no effective treatment options available, solutions are largely centered around lifestyle management, and current research is focused on identifying and modifying risk factors for cognitive declines, such as obesity.

Various studies have identified an association between cognitive function and obesity in middle-aged individuals, with longitudinal studies indicating that midlife obesity is a risk factor for dementia.

However, the results from studies investigating the correlation between obesity and the risk of dementia in older adults remain conflicting. This could be due to factors such as not accounting for confounding variables, such as heterogeneity in the study population based on age or inadequate cognitive function tests.

About the study

In the present study, the researchers analyzed the association between BMI and temporal changes in cognitive abilities of a cohort of community-dwelling adults over 65.

The association between BMI and cognitive function was analyzed separately for individuals between the ages of 65 and 75 and those above 75.

Furthermore, a comprehensive set of neuropsychological tests were used to assess cognitive function, and the researchers adjusted the analyses for potential confounders.

The participants were recruited for the Hellenic Longitudinal Investigation of Aging and Diet (HELIAD) study, which studied the epidemiology of various neuropsychiatric conditions related to aging, such as Alzheimer's disease, mild cognitive impairment, and dementia.

Information on lifestyle and other domains was collected through interviews, with the involvement of caregivers wherever necessary.

The height and body weight of the participants were measured to calculate the BMI according to the World Health Organization (WHO) recommendations. Measurements were taken at baseline and during the first follow-up.

The neuropsychological evaluation consisted of a comprehensive set of tests that measured various cognitive domains such as attention and procession speed, verbal and non-verbal memory, executive functioning, visuospatial ability, and language.

Clinical diagnoses of dementia and mild cognitive impairment were determined based on consensus from a team of neurologists and neuropsychologists using established diagnostic criteria.

Depression or depressive symptoms were assessed based on a self-reported questionnaire, current medications, and examinations by neurologists.

Demographic data of age, sex, and education levels were also collected, and blood samples were obtained for apolipoprotein E genotyping to determine genetic predisposition to neurodegenerative diseases.

Results

The results suggested that changes in BMI and obesity were associated with a temporal change in cognitive performance, with the associations being modified with age.

For individuals at or below the age of 75, weight loss moving from obesity towards a normal BMI was associated with a lower rate of memory decline, while no change in BMI for three years was linked to a longitudinal decrease in visuospatial ability.

In contrast, among individuals over 75, obesity was associated with a slower rate of memory decline, and a change in BMI from obesity to normal weight contributed to a more rapid decline in the attention and processing speed domains of neurocognitive function.

The authors believe that the contrast in results for the two groups could be explained by the difference in characteristics of the two age groups, with older individuals having more comorbidities or chronic illnesses being more susceptible to changes such as weight loss.

Additionally, the obesity paradox regarding the inverse relationship between obesity and cognitive impairment is explained by the long preclinical phase of dementia.

Weight loss in adults above 75 could result from pathological changes that manifest before dementia is diagnosed. Factors such as impaired olfaction, initiative loss, predementia apathy, and difficulty eating could contribute to weight loss.

Frailty associated with progressing age could also explain weight loss and cognitive decline due to oxidative stress and inflammation.

Conclusions

Overall, the results suggested that weight loss and temporal decline in cognitive function had a negative association in adults between the ages of 65 and 75.

While in individuals older than 75, obesity was associated with a slower memory decline, and weight loss was associated with a more rapid decline in processing ability and attention.

Journal reference:
Dr. Chinta Sidharthan

Written by

Dr. Chinta Sidharthan

Chinta Sidharthan is a writer based in Bangalore, India. Her academic background is in evolutionary biology and genetics, and she has extensive experience in scientific research, teaching, science writing, and herpetology. Chinta holds a Ph.D. in evolutionary biology from the Indian Institute of Science and is passionate about science education, writing, animals, wildlife, and conservation. For her doctoral research, she explored the origins and diversification of blindsnakes in India, as a part of which she did extensive fieldwork in the jungles of southern India. She has received the Canadian Governor General’s bronze medal and Bangalore University gold medal for academic excellence and published her research in high-impact journals.

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