Trends, Determinants, and Associations of Treated Hypothyroidism in the United Kingdom, 2005-2014

Abstract

Background: Recent reports suggest that prescriptions for thyroid hormones have increased. Recent trends in and determinants of the prevalence of treated hypothyroidism across the United Kingdom were therefore analyzed.

Methods: Data covering the whole of the United Kingdom held by the National Health Service and the Office of National Statistics were examined. The main outcome measured was trends in the prevalence of treated hypothyroidism between 2005 and 2014. In addition, linear trend forecasting was performed to estimate projected trends in the prevalence of treated hypothyroidism up to the year 2025. Furthermore, determinants of variation of treated hypothyroidism prevalence across each of the 237 health areas in the United Kingdom in 2014 and its association with other health conditions were explored by multivariate linear regression analyses.

Results: The prevalence of treated hypothyroidism increased from 2.3% (1.4 million) to 3.5% (2.2 million) of the total British population between the years 2005 and 2014 and is projected to rise further to 4.2% (2.9 million) by 2025. There was large geographical variation of treated hypothyroidism across the United Kingdom, with London having the lowest (1.4%) and the Western Isles of Scotland having the highest (6.3%) prevalence. This variation was attenuated, but did not completely disappear, after some potential determinants were accounted for. The prevalence of treated hypothyroidism was independently related to health areas, with a higher proportion of individuals who were female, white, and obese, and negatively associated with prevalent cigarette smoking. The prevalence of treated hypothyroidism was significantly associated with the frequency of prevalent atrial fibrillation but not with other major health conditions, including ischemic heart disease and osteoporosis.

Conclusions: Between 2005 and 2014, the prevalence of treated hypothyroidism increased across the United Kingdom, has wide geographical variation, and is likely to increase further for the foreseeable future. Clinical effects and cost-effectiveness of the trend in increasing treatment of hypothyroidism remains to be evaluated.

Keywords: determinants of treatment; levothyroxine prescribing; trends in hypothyroidism; variation in treatment.