Irisin and its relation to insulin resistance and puberty in obese children: a longitudinal analysis.

CONTEXT: Irisin is a recently identified myokine affecting metabolic and glucose homeostasis. However, the role of irisin in obesity and its metabolic consequences are controversial, and data in children are scarce.

OBJECTIVE

To study the relationships between irisin, insulin resistance, and puberty before and after weight loss in obese children with and without impaired glucose tolerance.

DESIGN

One-year follow-up study in obese children participating in a lifestyle intervention.

SETTING

Primary care.

PATIENTS: Forty obese children and 20 normal-weight children of similar age, gender, and pubertal stage.

INTERVENTION: A 1-year outpatient intervention program based on exercise, behavior, and nutrition therapy.

MAIN OUTCOMES MEASURES: Fasting serum irisin, weight status (body mass index [BMI] SD score), and the following parameters of the metabolic syndrome: insulin resistance index (homeostasis model of assessment), blood pressure, and lipids.

RESULTS

The irisin levels were the highest in obese children with impaired glucose tolerance, followed by obese children with normal glucose tolerance, and levels were lowest in normal-weight children (P < .001). In a multiple linear regression analysis, baseline irisin was significantly associated with pubertal stage, high-density lipoprotein-cholesterol, and homeostasis model of assessment, but not to age, gender, BMI, or any other parameter of the metabolic syndrome. The irisin concentrations were significantly (P = .010) lower in the prepubertal compared to the pubertal children. In longitudinal analyses, changes of irisin were significantly associated with entry into puberty, change of fasting glucose, and 2-hour glucose in an oral glucose tolerance test, but not with change of BMI or any other parameter.

CONCLUSIONS

Irisin levels are related to pubertal stage and insulin resistance but not to weight status in childhood.