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Body mass index (BMI) has been linked to inflammation, and systemic inflammation has been linked to decreased cognition. Now, a new study directly links a high BMI to lower cognitive functioning. The current study, published in the journal Brain, Behavior, and Immunity, is the first step in identifying a biologically plausible mechanism for the connection between BMI and cognition.
The authors evaluated 2 cohorts of people aged 50 years and older from the English Longitudinal Study of Aging. One group contained 9000 people and the other contained approximately 12,500.
When the authors correlated BMI, inflammatory markers, and cognition over a 6-year period, the results in both groups were the same: higher BMI was associated with greater cognitive decline.
Specifically, the higher the BMI at the beginning of the study, the greater increase in levels of inflammatory markers (specifically, C-reactive protein [CRP]) over the next 4 years. The change in CRP predicted greater decline in memory and executive functioning over the following 2 years (a total of 6 years from the start of the study.) Established literature already links inflammation to cognitive decline, but these findings take it a step further by highlighting the role of BMI in systemic inflammation.
Physical activity and body mass are related to cognitive function in adults. BMI is a function of body mass (i.e., weight) and height, and most data reveal an inverse relationship between physical activity and BMI. Likewise, regular exercise has been shown to prevent cognitive decline in adults who are middle aged and older.
The relationship between physical activity and BMI, however, is nuanced because BMI does not account for a person’s amounts of body fat or muscle mass, both of which can skew the calculation. Still, the general trends are intuitive: engage in more physical activity, decrease body weight, lower BMI, and improve cognition.
In the current study, BMI, by way of inflammation, predicted cognitive decline. While no absolute criteria are reported for preventing cognitive decline, the authors provide one more reason – if one is even needed – to maintain an appropriate body weight and levels of physical activity. Changes in cognition related to aging often take years – even decades – to appear, so a healthy BMI at younger ages may prevent cognitive changes years later.
A recent landmark study indicated that healthy lifestyle habits were cumulative in their protective effects against cognitive decline, asserting that exercise and maintaining health body weight were important for 20 years before the onset of cognitive decline.
Healthy BMI is correlated to decreased risks of many diseases and conditions that affect most of the major body’s major organ systems. Now, simply reducing BMI may be a simple, low-cost intervention to decrease the burden of cognitive impairment.
Bourassa, K., & Sbarra, D. A. (2016). Body mass and cognitive decline are indirectly associated via inflammation among aging adults. Brain, Behavior, and Immunity. doi:10.1016/j.bbi.2016.09.023
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Willey, J. Z., Gardener, H., Caunca, M. R., Moon, Y. P., Dong, C., Cheung, Y. K., … Wright, C. B. (2016). Leisure-time physical activity associates with cognitive decline. Neurology, 86(20), 1897–1903. doi:10.1212/wnl.0000000000002582
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