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.