Elderly people with slightly raised thyroid hormone concentrations-but who do not have overt thyroid disease-could be at an increased risk of death from cardiovascular disease, suggest authors of a study in this week’s issue of THE LANCET.
Low blood concentration of the hormone thyrotropin is a marker of thyroid-gland overactivity (hyperthyroidism); hyperthyroidism is associated with metabolic disorders, and cardiovascular disease. Low thyrotropin concentrations in combination with normal thyroid-hormone concentrations describe individuals with mild or subclinical hyperthyroidism, which is common in elderly people and in individuals with a history of thyroid disease. Jayne Franklyn and colleagues from the University of Birmingham, UK, and the European Institute of Oncology, Milan, Italy, aimed to assess the long-term effects of subclinical hyperthyroidism on death rates among older people.
1191 individuals from a primary-care practice in Birmingham, UK, who were aged 60 years or older and who were not on thyroxine or antithyroid medication, were studied. Concentration of blood thyrotropin was measured in 1988-89, and individuals were followed up ten years later; causes of death were identified for individuals who had died. The investigators compared data for causes of death with age-specific, sex-specific, and year-specific data from the general population in England and Wales. They also compared mortality within the study population according to initial thyrotropin measurement.
The overall death rate in the study population was similar to the general population. However, death from all causes doubled in the first five years of follow-up among individuals with low thyrotropin concentrations; death caused by cardiovascular disease was up to three times more likely compared with individuals who had normal thyrotropin concentrations.
Jayne Franklyn comments: “Our findings lend support to the view that people with persistently reduced concentrations of thyrotropin in their serum should be considered for treatment (typically with radioactive iodine) to restore biochemically normal thyroid function, with the objective of reducing the described increase in mortality from vascular diseases. A prospective trial needs to be done to assess this intervention.”
In an accompanying Commentary (p 856), Vahab Fatourechi from the Mayo Clinic, USA, concludes: “Irrespective of the thyrotropin concentration needed for the diagnosis of subclinical hyperthyroidism, guidelines for therapy of low serum thyrotropin values will depend on interpretation of previously reported studies and confirmation of Parle and colleagues’ findings. Randomised studies may not be ethically justified in patients with thyroid diseases and thyrotropin concentrations less than 0·1 mU/L, but randomised trials for slightly low serum thyrotropin values (0·1-0·5 mU/L) are needed to guide management.”
Contact: Professor Jayne Franklyn, Division of Medical Sciences, University of Birmingham, Queen Elizabeth Hospital, Edgbaston, Birmingham B15 2TH, UK. T) +44 (0)121 627 2381; F) +44 (0)121 627 2384; E) j.a.franklyn@bham.ac.uk
Dr Vahab Fatourechi, Division of Endocrinology, Metabolism, Nutrition, and Internal Medicine, Mayo Clinic, Rochester, MN 55905, USA; E) fatourechi.vahab@mayo.edu
Journal
The Lancet