Relations of thyroid function to body weight

Background: Overt hypothyroidism and hyperthyroidism maybe associated with weight gain and loss. We assessed whether variations in thyroid function within the reference (physiologic) range are associated with body weight. Methods: Framingham Offspring Study participants (n=2407) who attended 2 consecutive routine examinations, were not receiving thyroid hormone therapy, and had baseline serum thyrotropin (TSH) concentrations of 0.5 to 5.0 mIU/L and follow-up concentrations of 0.5 to 10.0 mIU/L were included in this study. Baseline TSH concentrations were related to body weight and body weight change during 3.5 years of follow-up. Results: At baseline, adjusted mean weight increased progressively from 64.5 to 70.2 kg in the lowest to highest TSH concentration quartiles in women (P < .001 for trend), and from 82.8 (lowest quartile) to 85.6 kg (highest quartile) in men (P=.007 for trend). During 3.5 years of follow-up, mean (SD) body weight increased by 1.5 (5.6) kg in women and 1.0 (5.0) kg in men. Baseline TSH concentrations were not associated with weight change during follow-up. However, an increase in TSH concentration at follow-up. was positively associated with weight gain in women (0.5-2.3 kg across increasing quartiles of TSH concentration change; P < .00 I for trend) and men (0.4-1.3 kg across quartiles of TSH concentration change; P=.007 for trend). Conclusions: Thyroid function (as assessed by serum TSH concentration) within the reference range is associated with body weight in both sexes. Our findings raise the possibility that modest increases in serum TSH concentrations within the reference range may be associated with weight gain.