Background: Subclinical hypothyroidism is defined as elevated TSH levels while T4 or FT4 levels are normal. Elevated TSH levels are linked with obesity in adults. In a recent meta-analysis in Iran, 6.1% of children below 18 had obesity. Due to the low number of studies on the subject in children we, designed the study to assess the relation between BMI Z-score and TSH levels in children and adolescence.
Method: This cross-sectional study was performed in a growth assessment clinic in Shiraz. Children aged between 2 to 18 years that came to the clinic for routine growth assessment follow up from January till April 2018 were considered. 850 children including 365 boys and 485 girls were included. Children with TSH between 0.3 and <10 mIU/L and normal free T4 (0.8-1.8 ng/dL) were included in the study. Participants with drugs or diseases affecting serum lipid or thyroid hormones were excluded. TSH levels equal or above 5 were considered abnormal. All participants with high TSH levels were considered for a second remeasurement. For these participants, second TSH levels were considered for the study. BMI Z-score was calculated by the LMS (lambda, mu, sigma) method based on the reference of BMI distribution of CDC growth charts.141 participants were defined as underweight below 5th percentile (<-1.65 BMI Z-score), 369 as healthy weight between 5th and 85th percentile (-1.65 +1.04 BMI Z-score), 116 as overweight between 85th and 95th percentile (+1.04 +1.65 BMI Z-score) and 224 as obese above 95th percentile (>+1.65 BMI Z-score).
Results: Prevalence of subclinical hypothyroidism is increased in higher BMI groups. 9.9%, 13.8%, 17.2% and 20.5% of underweight, healthy weight, overweight and obese had subclinical hypothyroidism respectively. Obese and overweight participants had higher odds of subclinical hypothyroidism than those who were not (OR: 1.649, P=0.010, CI95% 1.126 2.413). On the other hand, Subclinical hypothyroid participants had higher odds of overweight or obesity than those who were euthyroid (OR: 1.650, P=0.010, CI95% 1.128 2.413). When TSH is set as a dependent value, TSH level is increased (β=0.126, r=0.125, P=0.001) with an increase in BMI Z-score. When BMI Z-score is set as a dependent value, BMI Z-score is increased (β=0.113, r=0.243, P=0.001) with an increase in TSH level.
Conclusion: BMI Z-score and Subclinical hypothyroidism are positively correlated however studies should be performed on establishing the causality.
19 - 21 Sep 2019
European Society for Paediatric Endocrinology