No consensus exists whether subclinical thyroid disease should be treated or 
just observed. Untreated overt thyroid disease is associated with increased risk 
of cardiovascular disease, and this study was conducted to assess the risk of 
cardiovascular events in subclinical thyroid disease. The population-based 
prospective study was conducted in Denmark. A total of 609 subjects from general 
practice aged 50 years or above with normal left ventricular function were 
examined. During a median of 5 years of follow-up, major cardiovascular events 
were documented. In subjects with abnormal TSH at baseline, information about 
potential thyroid treatment during follow-up was obtained from case reports and 
mailings. At baseline, 549 (90.7%) were euthyroid (TSH 0.40-4.00 mU/l), 31 
(5.1%) were subclinical hypothyroid (TSH>4.00 mU/l), and 25 (4.1%) were 
subclinical hyperthyroid (TSH<0.40 mU/l). 1 overt hyperthyroid and 3 overt 
hypothyroid participants were excluded from the analyses. At baseline, the 
levels of NT-proBNP were inversely associated with the levels of TSH; the lower 
the levels of TSH, the higher the NT-proBNP concentration. During follow-up, 88 
participants died, 81 had a major cardiovascular event, and 28 had a stroke. The 
incidence of stroke was increased among subjects with subclinical 
hyperthyroidism, HR 3.39 (95% CI 1.15-10.00, p=0.027) after adjusting for sex, 
age, and atrial fibrillation. Subclinical hypothyroidism was not related with 
any of the outcome measurements. Subclinical hyperthyroidism seems to be a risk 
factor of developing major cardiovascular events, especially stroke in older 
adults from the general population with normal left ventricular function.