Subclinical hypothyroidism was associated with an increased risk for stroke in adults younger than 65 years and in those with higher levels of thyroid stimulating hormone, according to recent findings.
However, an increased overall risk for stroke events or fatal stroke does not appear to be linked to subclinical hypothyroidism, according to the researchers.
Robin P. Peeters, MD, PhD, of Erasmus University Medical Center in the Netherlands, and colleagues queried several online databases for published longitudinal studies through November 2013 that prospectively assessed baseline TSH and free thyroxin levels in adults and stroke events and/or fatal stroke. The researchers consulted the Thyroid Studies Collaboration to identify unpublished studies for analysis. Seventeen prospective cohort studies were identified for inclusion with a total of 47,573 participants.
The researchers extracted individual participant data pertaining to previous cardiovascular risk factors and disease, including total cholesterol, systolic blood pressure, history of diabetes, smoking status and prior cerebrovascular disease. The study’s primary outcome measures were stroke events and fatal stroke. The researchers defined normal thyroid levels as TSH levels of 0.45 to 4.49 mIU/L and subclinical hypothyroidism as TSH levels 4.5 to 19.9 mIU/L with normal thyroxin levels. Overall, 3,451 participants were classified as having subclinical hypothyroidism.
The researchers found that for the participants with subclinical hypothyroidism, the age- and sex-adjusted pooled HR was 1.05 (95% CI, 0.91-1.21) for stroke events and 1.07 (95% CI, 0.8-1.42) for fatal stroke.
In an age-stratified analysis, the researchers found that for participants aged 18 to 49 years the HR for stroke events was 3.32 (95% CI, 1.25-8.8). An increased risk for fatal stroke was also seen in the participants aged 18 to 49 years (HR = 4.22; 95% CI, 1.08-16.55) and those aged 50 to 64 years (HR = 2.86; 95% CI, 1.31-6.26; P for trend = .04).
No increased risk was observed in participants aged 65 to 79 years (HR = 1; 95% CI, 0.86-1.18) or those aged 80 years or older (HR = 1.31; 95% CI, 0.79-2.18).
Increased risk for fatal stroke corresponded to higher TSH levels; participants with TSH levels ranging from 7 to 9.9 mIU/L had an increased risk for fatal stroke compared with those with TSH levels in the normal range.
“Our data are reassuring for those over the age of 65 years and those with TSH levels between 4.5 and 6.9 mIU/L, who represent most participants with subclinical hypothyroidism,” the researchers wrote. “Whether treatment of subclinical hypothyroidism will result in a decrease of risk of stroke in younger subjects or those with higher TSH levels to be answered by a sufficiently powered randomized clinical trial.” – by Jennifer Byrne
Disclosure: Peeters reports financial ties with Genzyme. Please see the full study for a complete list of all other authors’ relevant financial disclosures.