Patients with thyroid-stimulating hormone (TSH) values at high-normal range may actually experience greater health benefits than those with lower laboratory ranges. Research results published in Diabetes Research and Clinical Practice are generating new conversations about the interplay between thyroid function and risk of stroke. 

A study conducted by Tamar de Vries, MD and PhD candidate in Internal Medicine in the Department of Vascular Medicine at the University Medical Center of Utrecht, the Netherlands,  evaluated 1,265 patients with type 2 diabetes (T2D) and a normal-range TSH result to learn whether potential changes in risk (higher or lower) are associated with heart attack or any other heart disease events.

According to the study authors, “Thyroid dysfunction is a risk factor for cardiovascular disease. Whether thyroid function within the normal range is a risk factor for cardiovascular disease remains uncertain.” Therefore, the team set out to determine whether plasma TSH concentrations in the normal range were a risk factor for cardiovascular (CV) disease and mortality in patients with normal-range TSH values (defined as 0.35-5.00 mIU/L) who also were diagnosed with T2D and had high CV risk scores. These participants were all from the Second Manifestations of ARTerial disease cohort. Using Cox proportional-hazards models, the team analyzed the data to determine the primary outcome, which was occurrence of a major CV event (MACE), including vascular death, stroke, and myocardial infarction. Secondary outcomes were other vascular outcomes and all-cause mortality. 

The study reported 191 MACE events, including 54 strokes, during the follow-up period. The team concluded, “Higher TSH levels within the normal range are associated with a lower risk of stroke in high-risk patients with type 2 diabetes, but not associated with the risk of other cardiovascular events or mortality.” The researchers found no relationship between plasma TSH levels and MACE (hazard ratio [HR] 0.93; 95% confidence interval [CI] 0.80-1.08). Conversely, they found that plasma TSH was associated with a lower risk of stroke (HR per mIU/L 0.64, 95% CI 0.45-0.89). Lastly, the researchers determined that there is no relationship between plasma TSH levels and risk of myocardial infarction, vascular death, or all-cause mortality.

In a recent interview, Dr. DeVries commented that the only observed CV outcome that corresponded with TSH levels was the risk of stroke. She also suggested that there was a possible protective effect with this higher range of normal TSH. “There are two main mechanisms that may be implicated in the reduced stroke risk associated with higher TSH levels,” she said. “However, it’s important first to realize that TSH has an inverse with thyroid hormone (T3 and T4) levels.”

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