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Moderate weight loss may reduce triiodothyronine, influence thyroid homeostasis
Moderate weight loss through caloric restriction appears to yield a decrease in serum triiodothyronine and may affect thyroid hormone stability, according to recent study findings.
Researchers for the longitudinal intervention study enrolled 47 participants with a BMI of 25 to 45, with 30 non-overweight individuals included as controls. The overweight volunteers participated in a weight-loss intervention group, which consisted of at least six inpatient visits for thorough metabolic evaluation. The control group participated in a single inpatient visit to facilitate the cross-sectional evaluation of the link between thyroid hormone and metabolic factors.
The 12-month weight-loss intervention initiated by obese and overweight participants involved individualized diet plans designed to achieve a caloric deficit of approximately 500 kcal/day to 1,000 kcal/day. The goal for the 12-month period was 5% to 10% weight loss. At least 150 minutes per week of moderate-intensity aerobic exercise was encouraged, and intervention study participants were availed of diet/lifestyle education by registered dieticians.
Patients in the weight-loss intervention group were seen for follow-up visits at 1.5, 3, 6, 9 and 12 months. At each inpatient visit, this group underwent the following: fasting blood work, anthropometrics, indirect calorimetry, DXA scan and nutrition counseling.
The researchers found that the weight-loss plan yielded a 6.3 kg (6.5%) weight loss in the intervention group. Although baseline thyroid-stimulating hormone and T3 levels were found to be significantly correlated with fat mass at baseline (P=.024 and P=.005, respectively), T3 decreased significantly after weight loss (from 112.7 ng/dL to 101.8 ng/dL, P<.001) without correspondingly significant changes in TSH or free thyroxine. An association was seen between the decrease in weight and the reduction in serum T3 (P<.001). There was a significant reduction in the T3 to free T4 ratio (P=.02) in those who lost >5% of their body weight.
These findings suggest that moderate weight loss may have an effect on the hypothalamic-pituitary-thyroid axis. Previous studies of this effect have primarily been focused on drastic weight loss, the researchers said.
“The type of intervention was aimed by design to achieve a moderate weight loss, that is, the type of weight loss commonly achievable in the community setting,” the researchers wrote. “Hence, the results are applicable to the general population.”
Disclosure: The researchers report no relevant financial disclosures.