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Obesity, metabolic status tied to cognitive decline
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Adults who are obese and have metabolic abnormalities experienced faster cognitive decline vs. those with normal weight, according to study results published in Neurology.
Metabolic abnormality was defined in the study as having two or more of the following:
- High triglyceride levels or taking lipid-lowering drugs.
- High blood pressure or taking drugs for high blood pressure.
- High glucose levels or taking diabetes medication.
- Low HDL cholesterol levels.
Archana Singh-Manoux, PhD, of the National Institute of Health and Medical Research in Paris, and colleagues examined data on 6,401 adult men and women aged 39 to 63 years who were part of the Whitehall II study. Data on BMI and metabolic risk factors were gathered at the beginning of the study, and study participants completed four cognitive tests three times during a 10-year period. The tests measured memory, reasoning, and semantic and phonemic fluency.
Thirty-one percent of the men and women had metabolic abnormalities, whereas 52.7% were normal weight, 38.2% were overweight and 9.1% were obese. Of the 582 adults who were obese, 60.1% were categorized as being metabolically abnormal.
Among those who were metabolically normal, 10-year cognitive decline was similar (P=.36) for normal weight (95% CI, –0.42 to –0.38), overweight (95% CI, –0.45 to –0.39) and obese (95% CI, –0.50 to –0.34) subgroups. However, among those who were metabolically abnormal, cognitive decline was faster in obese adults (95% CI, –0.55 to –0.42) compared with normal-weight adult (95% CI, –0.50 to –0.34).
Singh-Manoux and colleagues said the results provide evidence against the concept of “metabolically healthy obesity.”
“If the concept of [metabolically healthy obesity] holds, then the estimation of the negative impact of obesity on health needs to be revisited,” the researchers wrote. “Our data suggest no such heterogeneity in the impact of obesity on cognitive performance in early old age, because obese individuals who are otherwise metabolically healthy have a risk of poor cognition similar to that of their obese metabolically unhealthy counterparts.”
Disclosure: Dr. Singh-Manoux receives research support from the National Institutes of Health, the National Institute on Aging and the British Medical Research Council. See the study for the full list of financial disclosures.
Perspective
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Elaine H. Morrato, DrPH, MPH, CPH
This important paper adds to the literature on obesity and its association with adverse chronic conditions, specifically cognitive decline.
Epidemiology studies have suggested that overweight and obesity, particularly in midlife, are risk factors for later development of dementia. Some studies have suggested that obesity coupled with clinical metabolic abnormalities conveys greater risk than obesity with normal metabolic markers. However, the evidence is unclear whether these are causal effects.
This study (nested within the Whitehall II cohort) is notable because it prospectively followed over 6,000 adults over 10 years with rigorous measurement of cognitive function (memory, reasoning, semantic and phonemic fluency) and clinical assessment of metabolic abnormalities (serum triglycerides, HDL cholesterol, glucose, blood pressure and use of lipid-lowering, antihypertensive and diabetes medications). The Whitehall studies of British civil servants have been landmark in revealing how socioeconomic differences affect physical health, mental illness and mortality.
In the present study examining cognitive performance, there were two take-home messages for me. First, baseline cognitive function was lower with increasing BMI only among metabolically healthy individuals. Normal weight individuals with metabolic abnormalities already had a similar cognitive deficit as their obese counterparts. Second, although individuals with metabolic abnormalities showed greater cognitive decline over 10 years, being metabolically healthy or not was not associated with differences in decline if the individual was already obese in midlife.
The obesity epidemic in the United States is well known. One in three adults (about 75 million Americans) is obese. This study adds to the growing evidence of adverse effects of obesity on health. It refutes the notion that metabolically normal obese adults have a better cognitive outlook than obese adults with metabolic abnormalities.
For more information on strategies to combat obesity, please see the following resources:
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