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Childhood free T3 levels tied to pubertal stage at 13 years
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Free triiodothyronine levels at age 7 years were higher among boys and girls with a more advanced pubertal stage at age 13 years, whereas free thyroxine and thyroid-stimulating hormone levels were not associated with pubertal stage, according to published findings.
Peter Taylor, MBChB, MSc, of the Thyroid Research Group, Systems Immunity Research Institute at Cardiff University School of Medicine, United Kingdom, and colleagues evaluated data from the Avon Longitudinal Study of Parents and Children on 4,442 children who had thyroid function measured at age 7 years, 1,263 children who had thyroid function measured at age 15 years and 884 children who had thyroid function measured at both ages to determine changes in TSH and thyroid hormone levels over childhood.
The mean TSH value was 2.26 mU/L, mean free T3 was 6.29 pmol/L and mean free T4 was 15.7 pmol/L at age 7 years. Overall, 23.2% of participants had free T3 above the adult reference range, 3.65% had TSH above the adult reference range and 0.2% had free T4 above the adult reference range at age 7 years.
The mean TSH value was 2.43 mU/L, mean free T3 was 5.83 pmol/L and mean free T4 was 15.5 pmol/L at age 15 years. Overall, 12.2% of participants had free T3 above the adult reference range.
From age 7 to 15 years, TSH levels rose, whereas free T3 and free T4 fell. TSH levels increased by 0.03 mU/L (P < .001) every 2 years from age 7 to 15 years. Baseline TSH levels were higher among boys compared with girls at age 7 years (P < .001). Free T3 levels fell by 0.12 pmol/L every 2 years from age 7 to 15 years, and baseline free T3 levels were higher in girls compared with boys (P < .001). Free T4 levels fell by 0.04 pmol/L every 2 years (P = .005), and baseline free T4 levels were higher in girls compared with boys (P < .001).
Overall, 2,702 participants had pubertal status self-assessed at age 13 years. Tanner score was higher in girls (3.63) compared with boys (2.96; P < .0001). TSH levels at age 7 years were not associated with pubertal status at age 13 years in boys (P = .89) or girls (P = .31); the same was true for free T4 levels at age 7 years in boys (P = .32) or girls (P = .52). At age 7 years, free T3 levels were higher in boys (P = .0001) and girls (P = .04) who had more advanced puberty at 13 years.
“Our results demonstrate that thyroid hormone levels change substantially during childhood and adolescence,” the researchers wrote. “This is particularly the case with [free] T3, which is substantially higher in younger children. [Free] T3 levels also appear to influence the onset of puberty; further studies into the pituitary-thyroid axis in normal childhood populations are therefore needed to define the role of higher [free] T3 levels in childhood more precisely.” – by Amber Cox
Disclosure: The researchers report no relevant financial disclosures.
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