Thyroid function and body weight: a community-based longitudinal study

Abstract

Objective: Body weight and overt thyroid dysfunction are associated. Cross-sectional population-based studies have repeatedly found that thyroid hormone levels, even within the normal reference range, might be associated with body weight. However, for longitudinal data, the association is less clear. Thus, we tested the association between serum thyrotropin (TSH) and body weight in a community-based sample of adult persons followed for 11 years.

Methods: A random sample of 4,649 persons aged 18-65 years from a general population participated in the DanThyr study in 1997-8. We included 2,102 individuals who participated at 11-year follow-up, without current or former treatment for thyroid disease and with measurements of TSH and weight at both examinations. Multiple linear regression models were used, stratified by sex and adjusted for age, smoking status, and leisure time physical activity.

Results: Baseline TSH concentration was not associated with change in weight (women, P = 0.17; men, P = 0.72), and baseline body mass index (BMI) was not associated with change in TSH (women, P = 0.21; men, P = 0.85). Change in serum TSH and change in weight were significantly associated in both sexes. Weight increased by 0.3 kg (95% confidence interval [CI] 0.1, 0.4, P = 0.005) in women and 0.8 kg (95% CI 0.1, 1.4, P = 0.02) in men for every one unit TSH (mU/L) increase.

Conclusions: TSH levels were not a determinant of future weight changes, and BMI was not a determinant for TSH changes, but an association between weight change and TSH change was present.

Figure 1. Flow chart of the study group.

TSH serum thyrotropin.

Figure 2. Unadjusted regression lines for weight change tertiles in women (n = 1,577).

11-year weight change was divided in three groups, a lower, middle and upper tertiles. In the adjusted regression model, regression coefficients (β) for the association between Δfree T4 and ΔTSH differed significantly in the three groups (P<0.0007 for the interaction between Δfree T4 and Δweight tertiles), and was estimated to: β_{lower Δ weight tertile} = −0.047 mU/L (CI, −0.096, −0.0018), β_{middle Δ weight tertile} = −0.049 mU/L (CI, −0.093, −0.005), and β_{upper Δ weight tertile} = −0.150 mU/L (CI, −0.191, −0.109). Note the lines of the lower and middle weight change tertiles are difficult to distinguish from each other. Adjustments were made for age group (categorical), change in smoking status, change in leisure time physical activity, and for the baseline value of the outcome.