Purpose: The aim of this study was to estimate the 1-year prevalence of levothyroxine-treated hypothyroidism in Finland.
Methods: Data on all individuals who had regularly purchased levothyroxine sodium tablets during 2007 were retrieved from the nationwide Finnish Drug Prescription Database. The prevalence rates and 95% confidence intervals were calculated per 100 individuals assuming a Poisson distribution.
Results: In total, 189,027 individuals (84% female) were identified as using levothyroxine tablets, which translated into a 1-year prevalence of hypothyroidism of 3.6%. The disease was notably more common in females (5.9%) than in males (1.2%), with a gender prevalence rate ratio (PRR) of 4.5. Prevalence increased with age. A comparison of five university hospital districts revealed that the prevalence rates were fairly stable regionally, with the lowest rate being 3.1% and the highest 4.4%; the regional PRR was 1.3.
Conclusions: To the best of our knowledge, this nationwide prescription study includes the largest population of reported levothyroxine users to date. This comprehensive data justifies estimating the gender- and age-specific prevalence of hypothyroidism in Finland.