Introduction: The association between fatigue, functional status and subclinical hypothyroidism (SCH) remains unclear. The available data is not consistent, and this is likely to be due to selection bias in studies recruiting patients from clinic rather than unselected community populations. Only population surveys looking at prevalence of fatigue and functional status in SCH are likely to provide the answer.
Objective and Methodology: We compared the prevalence of fatigue and functional status between subjects with SCH and euthyroid controls, identified in the Whickham 20 year follow up survey. SCH was defined as those with serum TSH 4.510.0 mIU/L and normal free thyroxine levels. Individuals with known thyroid disease were excluded. Fatigue was reported as a binary (yes/ no) response. The functional status was assessed using Modified Rankin Scale (MRS). The individuals were unaware of their thyroid status at the time of symptom assessment. Multivariate analysis was performed with fatigue as dependent variable, and age, gender, thyroid status, diabetes mellitus, ischaemic heart disease and cereberovascular disease as the co-variates.
Results: There were 1367 euthyroid individuals (mean age 58.4 years, 50.8% females and mean serum TSH 1.8 mIU/L) and 62 individuals with SCH (mean age 59.6 years, 61.3% females and mean serum TSH 5.9 mIU/L). The prevalence of fatigue and impaired functional status was higher in SCH than euthyroid controls; 25.8% vs. 15.4%, P=0.028 and 56.5% vs. 43.5%, P= 0.01, respectively. For the whole group, males and females; the odds ratios (OR) for fatigue in subjects with SCH compared to euthyroid controls were 1.83 (95%CI 1.013.32, P=0.047), 3.29 (95%CI 1.318.26, P=0.011) and 1.33 (95% CI 0.622.89, P=0.475) respectively. Similarly, the OR for impaired functional status were 1.99 (95% CI 1.143.48, P=0.016), 3.56 (95% CI 1.418.98, P=0.007) and 1.36 (95% CI 0.662.79, P=0.399) for the whole group, males and females respectively.
Conclusion: This data from a large population-based study shows that in males (not in females) fatigue and impaired functional status are associated with SCH, independent of age and other co-morbidities. We need large prospective clinical trials to demonstrate whether treatment with thyroxine improves fatigue and functional status in SCH.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.