medwireNews: Severely obese people show evidence of impaired cognition even when they have no signs of prediabetes or diabetes, but retinopathy and nephropathy only occur in those with hyperglycemia, US research shows.
The team from the University of Michigan in Ann Arbor therefore believes that “[o]besity alone is likely sufficient to cause cognitive deficits but not retinopathy or nephropathy,” with central obesity a “key metabolic risk factor.”
The findings arose from a cross-sectional study of 138 severely obese individuals (BMI >40 kg/m2 or BMI >35 kg/m2 with at least one comorbid medical condition) who were due to undergo bariatric surgery and 46 lean controls.
As reported in Diabetes Care, the prevalence of cognitive deficit was 6.5% in lean controls, 22.2% in normoglycemic obese participants, 17.7% in obese participants with prediabetes, and 25.6% in obese participants with diabetes, based on a National Institutes of Health (NIH) Toolbox cognitive composite score below the fifth percentile for lean controls.
The corresponding prevalence of cardiovascular autonomic neuropathy (CAN; expiration-to-inspiration ratio below the control group fifth percentile) was 4.4%, 18.2%, 21.4%, and 31.9%.
Nephropathy (estimated glomerular filtration rate <60 mL/min per 1.73 m2 and/or albumin-to-creatinine ratio ≥30 mg/g) was present in 6.5%, 6.1%, 17.9%, and 16.3% of the control, obese normoglycemic, obese prediabetic, and obese diabetic groups respectively, while retinopathy was only detected among the obese participants with prediabetes or diabetes, at rates of 1.9% and 6.1%, respectively.
Regression analyses showed that obese participants with normoglycemia had significantly lower NIH Toolbox composite scores than the lean controls, but there was no significant difference between the two groups in the prevalence of nephropathy or retinopathy.
The researchers also investigated whether any components of metabolic syndrome were associated with their cognitive and traditional diabetic outcomes.
They found that waist circumference and high-density lipoprotein cholesterol were significantly and inversely associated with cognitive function whereas systolic blood pressure was positively associated with this outcome.
Waist circumference was also inversely associated with CAN, while prediabetes was inversely associated with retinal function.
“Taken together, our results indicate that central obesity is much more important than general obesity,” Brian Callaghan and co-authors remark.
They say: “Future studies need to focus on the mechanisms by which central obesity leads to peripheral and central nerve injury, including the potential difference in roles between subcutaneous and visceral adiposity.
“Interventions that shift adipose storage preferentially to non- central locations may help reduce many different complications of obesity.”
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