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Metabolic syndrome linked to reduced cognitive ability in adolescents

By Nicole Mackee
Adolescents with metabolic syndrome are at risk of falling behind academically, say US researchers who have found that the syndrome was associated with impaired reading, working memory and attention.

The researchers reported in Metabolic Syndrome and Related Disorders that adolescents with metabolic syndrome scored an average 1.25 points lower in reading examinations and an average 0.89 points lower in digit span examinations that measure working memory and attention, compared with adolescents without the syndrome.

The researchers tested for metabolic syndrome in 1170 National Health and Nutrition Examination Survey III participants aged 12 to 16 years, and found a weighted prevalence of metabolic syndrome in this sample of 10.4%. They assessed outcome measures using the Wide Range Achievement Test-Revised (for mathematics and reading) and the Wechsler Intelligence Scale for Children – Revised (for attention and working memory) tools.

The authors considered participants to have metabolic syndrome if they met three or more of the following criteria: HDL-C <50 mg/dL (<1.30 mmol/L; except in boys aged 15 to 19 years, in whom the cut-off point was <45 mg/dL [1.17 mmol/L]); waist circumference more than 75th percentile for sex and age; systolic blood pressure more than 90th percentile for sex, age and height; triglyceride levels 100 mg/dL (1.13 mmol/L) or more; and fasting glucose levels 110 mg/dL (6.11 mmol/L) or more.

Professor Kate Steinbeck, endocrinologist and inaugural Medical Foundation Chair in Adolescent Medicine at the University of Sydney, advised caution in interpreting the findings of this cross-sectional study. She said that definitions of metabolic syndrome vary and hence prevalence rates varied between studies. In this study insulin resistance was not assessed, she said.

She noted that the impact on cognition was modest and that the participants fell within the normal range of expected outcomes. However, she said, the study did reinforce the message that the metabolic syndrome should be avoided at all ages.

‘This was not a longitudinal study and very long-term studies that show how metabolic abnormalities in children develop into adolescence and beyond have not been done. Once a person is middle-aged, we know that the metabolic syndrome is likely to deteriorate – but we don’t have the clear trajectory data across childhood to adolescence to adulthood,’ Professor Steinbeck told Endocrinology Today.

She said a potential association between metabolic syndrome and adolescent cognitive ability made it even more important to address obesity and overweight in childhood.

‘It’s easier to intervene in unhealthy weight children, than in adolescents, when they may be more resistant to losing weight and being physically active, which we know can reverse the metabolic syndrome,’ she added.

The authors proposed several mechanisms for the association including neuroinflammation, oxidative stress, abnormal brain lipid metabolism, impaired vascular reactivity, or hippocampal or prefrontal cortex atrophy linked to insulin resistance.

Professor Steinbeck said in addition to these possible mechanisms, there could be several other factors at play, such as depression in obese or overweight teens, or sleep disordered breathing both of which could influence test performance.
Metab Syndr Relat Disord 2016; 14: 397-403.

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