High BMI in Early Adulthood Tied to Better Midlife Cognition

A higher body mass index (BMI) from early adulthood to midlife was associated with better midlife cognition, particularly among US men and Black adults, an analysis of Bogalusa Heart Study participants suggested.

“We expected to find what you would call the intuitive relationship — that is, greater BMI would be correlated to worse cognitive function in midlife,” lead author Kathryn Gwizdala, PhD, a clinical research consultant based in Chicago, told Medscape Medical News. “However, we found what we could consider to be a counterintuitive relationship — that is, greater BMI was correlated with better memory among certain sex and race groups.”

The team recognized that the use of BMI as a direct measure of adiposity has fallen out of favor. Therefore, Gwizdala said, “we have been transparent within the context of this study that BMI was used as a proxy measure of adiposity. As this measure has been often adopted for population-based studies due to its simplicity and correlation with adiposity measures, we do believe it still has merit for the investigation of this relationship.”

Better Global Cognition, Memory, Recognition

The Bogalusa Heart Study has followed participants from childhood to adulthood since

1973. Adiposity was measured using BMI at biannual visits from 1973 to 2src16, and cognition was measured in 1292 participants at midlife (ie, 4src-58 years of age) between 2src13 and 2src16. A majority of participants were women (59%) and 34% were Black American individuals.

BMI was collected by stadiometer at each visit from childhood to adulthood. The cognitive tests included logical memory I (narrative memory free recall); logical memory II (long-term narrative memory free recall); logical memory II R (long-term memory recognition); digit spans forward and backward; trail making tests A and B; and a global composite.

BMI was averaged within age epochs: Childhood/adolescence, early adulthood, and midlife. The mean BMI percentile for childhood/adolescence was within the healthy weight range, whereas average BMI in young adulthood and midlife were in the overweight and class 1 obesity ranges.

Participants had an average of 13.3 years of education, with educational attainment higher in women than in men, and higher in White American individuals than in Black American individuals.

Women had better average scores on the global cognitive measure, delayed recall tests, and Trails A and B than men, and White American individuals had better scores on average on all cognitive measures than Black American individuals.

Black American individuals had greater early adulthood and midlife BMIs than White American individuals did, and women had a higher midlife BMI on average than men.

Overall, the analysis found that greater BMI in early adulthood and midlife was associated with better global cognition and logical memory I, II, and II R among men. In addition, greater BMI in childhood/adolescence was associated with better logical memory II R among men.

Among Black American individuals, greater BMI in early adulthood and midlife was associated with better logical memory I and II performance.

The literature already shows “highly mixed” results when making associations between adiposity and cognition, the authors noted. Possible reasons that the current study found positive instead of worse associations between adiposity and cognition may be that prior studies differed in terms of attrition due to poor participant health, including the co-occurrence of elevated adiposity and low cognitive function.

Censoring high-BMI, low-cognitive-function individuals from the analysis could have led to an observed association between higher BMI and higher cognitive function, the authors suggested.

Another possibility is that “any cognitive effects of adiposity — positive or negative — critically depend on the moment in the lifespan when adiposity is measured, and thus inter-study differences in that measurement time point could have led to differing associations,” they wrote.

Behavioral and biological factors could have contributed to the observed sex difference. The prominent association between adiposity and cognition among Black American individuals could be because this population faces a number of disparities relative to White American individuals with respect to brain health. Those disparities “could have set the stage for an especially potent effect of adiposity on cognition in either direction (positive or negative),” according to the authors.

Regardless, Gwizdala said, “Your physiological health is important earlier in life and can have significant impacts that we may not see immediately but later down the line. What’s considered healthy can look different to every person depending on sex, race, and other biological factors, and that makes individualized, targeted medicine all the more important.”

‘Confounding Factors’

Commenting for Medscape Medical News, Priya Jaisinghani, MD, clinical assistant professor at NYU Grossman School of Medicine in New York City, said the study “adds to the existing body of literature on adiposity and cognition, which remains complex and inconsistent. While BMI is a convenient and widely used population level tool, it has well recognized limitations. It does not differentiate between lean mass and fat mass, fails to account for variations in body fat distribution, and overlooks gender and ethnic differences.”

Furthermore, said Jaisinghani, who was not involved in the study, “There are numerous confounding factors, including genetics, behavioral patterns, socioeconomic status, and broader social determinants of health, that may influence both adiposity and cognitive outcomes.”

Additional research could help clarify the associations found in this and other studies, she suggested. These could include incorporating biomarkers and neuroimaging to provide deeper insights into the biological mechanisms linking adiposity to cognitive outcomes; considering lifestyle factors such as diet, physical activity, sleep, and comorbidities that may mediate or confound the relationship between adiposity and cognition; and evaluating the impact of lifestyle modifications, incretin therapies, and metabolic surgery on cognitive function, which could offer insights into potential interventions to preserve or improve cognitive function.

This study was funded by the US National Institute on Aging and the Pennington Biomedical Research Foun