Relationship between thyroid-stimulating hormone and blood pressure in the middle-aged and elderly population

I NTRO D U C TIO NPatients with hypothyroidism often have concurrent diastolic hypertension and hyperlipidaemia, and are hence susceptible to the development of coronary heart disease.Previous studies have shown that hypertension occurs in 20%-40% of hypothyroid patients.(1,2) However, the association between hypertension and subclinical hypothyroidism or high normal thyroid-stimulating hormone (TSH), also known as thyrotropin, remains controversial.A large population-based study performed on the habitants of Norway showed a positive linear association between the normal reference range of TSH and blood pressure.(3) Ruhla et al found that a high normal TSH was associated with a 1.7-fold increased prevalence of metabolic syndrome, (4) and since hypertension and insulin resistance are important symptoms of metabolic syndrome, the authors suggested that high normal TSH may be a risk factor for hypertension and insulin resistance.A possible mechanism that could explain the association of increased TSH with increased blood pressure is endothelial dysfunction resulting from a reduction in nitric oxide availability, leading to increased systemic vascular resistance independent of hyperlipidaemia.(5) It was also revealed that endothelial dysfunction in subclinical hypothyroidism could be partially reversed by levothyroxine supplementation.(5) However, even though systemic vascular resistance is increased, blood pressure may remain nearly stable in subclinical hypothyroidism because of diminished cardiac output.Walsh et al found that subclinical hypothyroidism was not associated with hypertension in a Western Australian population.(6) The inconsistent results on the relationship of high normal TSH level with blood pressure warrant further investigations in large populations.In the present study, we explored the relationship between subclinical hypothyroidism or high normal TSH and blood pressure in a population.The study population was originally recruited during a health survey on the prevalence of thyroid disease and diabetes mellitus in the district of Baoshan in Shanghai, China.Since existing research conducted in other populations have suggested that insulin resistance may also be associated with blood pressure, (7,8) we investigated the relationships among serum TSH level, insulin resistance and blood pressure.