Thyroid Research Thyroid Research Archive Obesity

Body mass and serum thyrotropin are positively associated in normal subjects

(March 2006)

The background of the study. Some change in weight is common in patients with hyperthyroidism or hypothyroidism, and in normal subjects serum thyrotropin (TSH) concentrations may be positively related to body weight. In this study, the relationship between serum TSH and body-mass index was determined in a large population-based cohort.

How the study was done. Weight, height, and serum TSH were measured in 6164 adults living in Tromsø, Norway, in 2001. Among them, 2672 had the same measurements in 1994-1995. Only the subjects whose serum TSH concentrations were within the 2.5- to 97.5-percentile range were included, subdivided by smoking status (approximately 25 percent were smokers).

The results of the study. Serum TSH concentrations increased with age in women and men, smokers and nonsmokers, in the 2001 cohort. Among nonsmokers, the mean serum TSH concentration was 1.6 mU/L in women aged 30 to 39 years, and it was 2.3 mU/L in those aged >69 years; the respective values in men were 1.6 and 2.3 mU/L. The increase with age was smaller in the smokers.

There was a gradual increase in body-mass index with increasing serum TSH in both women and men. Among the nonsmoking women and men, the body-mass index in those in the highest quartile for serum TSH was 1.4 kg/m2 and 0.4 kg/m2 higher, respectively, than in those in the lowest quartile for serum TSH; after adjustment for age, only the difference in women was statistically significant. Considering serum TSH as a continuous variable, serum TSH concentrations were positively associated with body-mass index in both women and men who were nonsmokers (P<0.01 and P<0.05, respectively). In the smokers, body-mass index was not associated with either quartile of serum TSH or serum TSH as a continuous variable.

Among the 2672 subjects in whom serum TSH was measured in 1994-1995 and in 2001, 1725 had normal serum TSH values at both times and no change in smoking status. There was no association between the increase in body-mass index and the quartile of increase in serum TSH between 1994-1995 and 2001.

The conclusions of the study. In women and men who are nonsmokers, serum TSH concentrations are positively associated with body-mass index.

The original article. Nyrnes A, Jorde R, Sundsfjord J. Serum TSH is positively associated with BMI. Int J Obes (Lond) 2006;30:100-5.