Associations of TSH levels within the reference range with future blood pressure and lipid concentrations: 11-year follow-up of the HUNT study

Objective: In cross-sectional studies, TSH levels within the reference range have been positively associated with blood pressure and adverse serum lipid levels. In a prospective study, we aimed to determine whether differences in TSH levels within the reference range are associated with future levels of blood pressure and lipids. Design: We conducted a prospective population-based study. Methods: In 9709 women and 4644 men without previous thyroid disease who had a baseline TSH level of 0.45-4.5 mU/l, we studied the associations of baseline TSH levels with blood pressure and lipid levels at follow-up 11 years later. Results: Higher TSH levels at baseline were associated with higher systolic (P=0.002 in women) and diastolic (P=0.03 in women) blood pressure, non-HDL cholesterol (P=0.01 in men) and triglyceride (P=0.008 in men) levels and lower HDL cholesterol levels (P<0.001 in women and men) at follow-up, but the associations were very modest and not consistent between the sexes. Among people who remained free of thyroid disease, changes in TSH levels during follow-up were associated with concomitant changes in systolic and diastolic blood pressure, non-HDL cholesterol and triglyceride levels (all P<0.001), with similar results being observed for women and men. Thus, blood pressure and lipid levels increased among people with an increase in TSH levels and decreased among people with a decrease in TSH levels compared with people with no change in TSH levels. Conclusions: High TSH levels within the reference range may be associated with modestly higher future levels of blood pressure and adverse serum lipids. TSH levels may co-vary with blood pressure and lipid levels among people with apparently normal thyroid function.