Type and Extent of Somatic Morbidity before and after the Diagnosis of Hypothyroidism. A Nationwide Register Study

BACKGROUND Hypothyroidism has been linked with an increased risk of other morbidities, such as cardiovascular diseases and diabetes mellitus. However, the temporal relationship between these diseases and the diagnosis of hypothyroidism is not well illuminated. Such information may provide insight into causal relationships between hypothyroidism and other morbidities. AIM To investigate the type and extent of somatic morbidity before and after a diagnosis of hypothyroidism. METHODS Observational cohort study. From official Danish health registers, 2822 hypothyroid singletons were identified and matched 1:4 with non-hypothyroid controls and observed over a mean period of 6 years. Frequency of different morbidities was obtained by person-to-person linking in the registers. Logistic and Cox regression models were used to assess the risk of morbidity before and after the diagnosis of hypothyroidism, respectively. RESULTS Prior to the diagnosis of hypothyroidism there was a significantly increased risk of being diagnosed with cardiovascular diseases (odds ratio (OR) 1.37; 95% confidence interval (CI): 1.19-1.58), lung diseases (OR 1.25; 95% CI: 1.13-1.39), diabetes mellitus (OR 1.92; 95% CI: 1.61-2.29), as well as malignant diseases (OR 1.24; 95% CI: 1.06-1.45). Following the diagnosis of hypothyroidism there was a significantly increased risk of being diagnosed with cardiovascular diseases (hazard ratio (HR) 1.36; 95% CI: 1.15-1.60); lung diseases (HR 1.51; 95% CI: 1.30-1.75); and diabetes mellitus (HR 1.40; 95% CI: 1.11-1.77). CONCLUSIONS Prior to the diagnosis of hypothyroidism there is an excess risk of being diagnosed with cardiovascular diseases, lung diseases, diabetes mellitus, and malignant diseases. Following the diagnosis of hypothyroidism we demonstrate an increased frequency of cardiovascular diseases, lung diseases, and diabetes mellitus.