Abstract
Background: Obesity is associated with vascular risk factors that in turn, may increase dementia risk. However, higher body mass index (BMI) in late life may be neuroprotective. The possible neural mechanisms underlying the benefit of higher BMI on cognition in older adults are largely unknown. Thus, we used functional connectivity magnetic resonance imaging (fcMRI) to examine: (1) the relationship between BMI and functional brain connectivity; and (2) the mediating role of functional brain connectivity in the association between baseline BMI and change in cognitive function over a 12-month period.Methods:We conducted a 12-month, prospective study among 66 community-dwelling older adults, aged 70 to 80 years, who were categorized as: normal weight (BMI from 18.50 to 24.99); overweight (BMI from 25.00 to 29.99); and obese (BMI ≥ 30.00). At baseline, participants performed a finger-tapping task during fMRI scanning. Relevant neural networks were initially identified through independent component analysis (ICA) and subsequently examined through seed-based functional connectivity analysis. At baseline and 12-months, we measured three executive cognitive processes: (1) response inhibition; (2) set shifting; and (3) working memory.Results:Obese individuals showed lower task-related functional connectivity during finger tapping in the default mode network (DMN) compared with their healthy weight counterparts (p < 0.01). Lower task-related functional connectivity in the DMN at baseline was independently associated with better working memory performance at 12-months (p = 0.02). Finally, DMN functional connectivity during finger tapping significantly mediated the relationship between baseline BMI and working memory at 12-months (indirect effect: −0.155, 95% confidence interval [−0.313, −0.053]).Conclusions:These findings suggest that functional connectivity of the DMN may be an underlying mechanism by which higher BMI confers protective effects to cognition in late life.
Highlights
Obesity is a complex condition that is characterized by excess body fat and is associated with adverse health outcomes, such as hypertension (Dyer and Elliott, 1989; Kuczmarski et al, 1997), diabetes (Medalie et al, 1974), stroke (Hubert et al, 1983), sleep apnea (Millman et al, 1995), and cancer (Chute et al, 1991; Bostick et al, 1994)
default mode network (DMN) functional connectivity during finger tapping significantly mediated the relationship between baseline body mass index (BMI) and working memory at 12-months
These findings suggest that functional connectivity of the DMN may be an underlying mechanism by which higher BMI confers protective effects to cognition in late life
Summary
Obesity is a complex condition that is characterized by excess body fat and is associated with adverse health outcomes, such as hypertension (Dyer and Elliott, 1989; Kuczmarski et al, 1997), diabetes (Medalie et al, 1974), stroke (Hubert et al, 1983), sleep apnea (Millman et al, 1995), and cancer (Chute et al, 1991; Bostick et al, 1994). There are estimated to be over 1.4 billion overweight (body mass index [BMI] from 25.00 to 29.99 kg/m2) and 500 million obese (BMI ≥ 30) adults over the age of 20 years. Current evidence suggests that higher BMI in young and midlife are associated with greater cognitive decline in late life (Elias et al, 2003; Gunstad et al, 2007; Nilsson and Nilsson, 2009; Sabia et al, 2009). The Whitehall II Study, which followed 5131 individuals from young adulthood (25 years old) through midlife (44 years old) to late life (61 years or older), found that higher BMI over young and middle adulthood was associated with lower cognitive performance of executive functions and verbal working memory in late life (Sabia et al, 2009). We used functional connectivity magnetic resonance imaging (fcMRI) to examine: (1) the relationship between BMI and functional brain connectivity; and (2) the mediating role of functional brain connectivity in the association between baseline BMI and change in cognitive function over a 12-month period
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