High, low TSH levels may increase mortality, cardiovascular risks
High or low levels of thyroid-stimulating hormone may increase total mortality risk in adults, and low TSH may specifically increase the risks for incident cardiovascular disease, coronary heart disease and stroke, study data show.
Ville Lauri Johannes Langén, MD, of the department of health of the National Institute for Health and Welfare in Helsinki, and colleagues evaluated data from the Health 2000 survey on 5,211 Finnish adults to determine associations between TSH levels and total mortality, CVD outcomes and sudden cardiac death. Follow-up was a median 13.2 years.
Participants were grouped into three categories based on TSH levels: low TSH (< 0.4 mU/L; n = 108), normal TSH (0.4-3.4 mU/L; n = 4,834) or high TSH (> 3.4 mU/L; n = 269).
Overall, 13.6% of participants died during follow-up. Compared with participants with normal TSH, participants with low TSH (HR = 2.03; 95% CI, 1.37-3) or high TSH (HR = 1.7; 95% CI, 1.3-2.23) had an increased risk for total mortality. The finding persisted for high TSH levels in the multivariable models (HR = 1.34; 95% CI, 1.02-1.76), but not for low TSH levels.
During follow-up, 1.6% of participants died of sudden cardiac death, and the risk for death was higher among participants with high TSH compared with normal levels in the crude (HR = 2.32; 95% CI, 1.16-4.64) and multivariable (HR = 2.28; 95% CI, 1.13-4.6) models. There was no significant association between the risk for sudden cardiac death and low TSH.
The incidence of major cardiac events was highest (15.5%), followed by incident CVD (11.4%), coronary heart disease (7.7%) and stroke (4.5%). The risks for incident CHD (HR = 2.15; 95% CI, 1.3-3.55), stroke (HR = 2.09; 95% CI, 1.07-4.08), CVD (HR = 1.91; 95% CI, 1.23-2.95) and major adverse cardiac events (HR = 1.76; 95% CI, 1.19-2.6) were increased with low TSH levels compared with normal TSH levels. High TSH was associated with an increased risk for major adverse cardiac events (HR = 1.4; 95% CI, 1.06-1.84) compared with normal TSH levels.
Among participants without atrial fibrillation at baseline, 6% developed the disorder during follow-up. Low TSH was associated with a higher risk for incident atrial fibrillation compared with normal TSH in the crude model (HR = 2.45; 95% CI, 1.46-4.11), but not the multivariable model. There was no association between the risk for atrial fibrillation and high TSH.
“Our findings ... suggest that minor increases in TSH do not harbinger cardiovascular morbidity or an increased risk of mortality,” the researchers wrote. “Finally, to conclude precisely which TSH values could serve as cutoffs for the initiation of thyroid therapy, randomized clinical trials are still warranted.” – by Amber Cox
Disclosures: Langén reports grant support from the Betenia Foundation, the Emil Aaltonen Foundation, the State Research Funding of the Turku University Hospital expert responsibility area and the Turku University Foundation. Please see the study for all other authors’ relevant financial disclosures.