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The William Harvey Research Institute - Barts and The London

Thyroid function affects the risk of stroke via atrial fibrilation: a Mendelian Randomization study

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Heart attacks are one of the most common causes of death worldwide. Nearly one in six men and one in ten women die from heart disease, therefore identifying heart disease risk factors, especially those that could be modified through early lifestyle interventions, is specifically important. Previous epidemiological studies suggest that variations in normal range thyroid function are associated with cardiovascular disease. However, it is unclear whether these associations are causal or not.

In a new study published in the Journal of Clinical Endocrinology & Metabolism researchers investigate whether genetically determined variation in normal-range thyroid function is causally associated with the risk of stroke and Coronary Artery Disease, and then interrogated via which pathways any confirmed relations may be mediated. They also examined associations with cardiovascular diseases outside the normal-range thyroid function focusing on patients with Hashimoto’s (hypothyroidism) and Graves’ (hyperthyroidism) disease.  

Lead author Dr Eirini Marouli from Queen Mary University of London said: “We provide evidence that genetically determined higher thyroid stimulating hormone (TSH) levels within the normal range are causally associated with a lower risk of stroke and this effect is mediated by a decreased risk of atrial fibrillation. Hashimoto’s disease appears to be associated with an increased risk of coronary artery disease and this effect is mainly mediated via obesity (reflected by the body mass index).

Our results suggest that we need to assess thyroid hormone levels even within the normal range in order to have a better handle in predicting risk of developing cardiovascular disease, and more specifically stroke. 

Senior author of the study, Professor Panos Deloukas added “Understanding the causal relationship behind an observation such as the inverse relationship between thyroid function and cardiovascular risk is important in advancing our knowledge about the disease and has the potential to point towards treatment interventions to prevent disease.

Thyroid dysfunction affects 5-10% of the general population, therefore, the findings have potential clinical implications as they pave the way to consider future adjustment of thyroid function within the normal range in managing patients’ risk of stroke.  The results introduce variation in normal range thyroid function as a novel modifiable risk factor for stroke.

Dr Marouli said: “We aim to further disentangle the complex relationships between thyroid function including disease with different outcomes. Clinical trials could further confirm the necessity of future adjustment of thyroid function within the normal range.” 

Further information

Research publication:Thyroid function affects the risk of stroke via atrial fibrillation: a Mendelian Randomization study, Marouli E et al, Journal of Clinical Endcorinology & Metabolism