TSH, blood pressure, and lipid levels

Abstract

Researchers in Norway have found that high normal concentrations of TSH are associated with raised blood pressure and lipid levels, but only slightly. “Differences in normal thyroid function may be associated with differences in future blood pressure and lipid levels but the strength of the association suggests that the finding may not be clinically relevant”, the authors concluded. The prospective population-based study, which had a follow-up period of 11 years, examined 9709 women and 4644 men with serum TSH levels within the reference range (0·45–4·5 mU/L) at baseline.Cross-sectional studies have shown that people with substantially raised TSH concentrations have high blood pressure and adverse lipid profiles. However, this finding is no more than an association, and causation remains unproven. Nonetheless, one possibility is that high TSH levels are an indicator of a low-functioning thyroid gland that is producing relatively low amounts of thyroxine, which raises blood pressure and lipid concentrations. “We do have thyroid hormone receptors in the heart so it is possible that subtle thyroid hormone deficiencies are linked directly to reduced thyroid hormone action in the vascular system,” suggests Kristien Boelaert (University of Birmingham, UK).“Our study found a more modest association than we expected based on cross-sectional studies involving individuals with TSH within the reference range”, said lead author Bjorn Olav Asvold. “One possible explanation could be that TSH co-varies with blood pressure and lipid levels rather than having a long-term effect.” Their study showed indications of this association, with patients' blood pressures and lipid levels increasing and decreasing in line with TSH concentrations. Perhaps a common cause is at work. Asvold suggests fat—in that leptin secreted from adipose tissue might stimulate TSH production, and high blood pressure and lipid levels often accompany adiposity.For future research, clarification of the effects of thyroid hormones on the heart will be useful. “It is important to know whether thyroid function influences the risk of cardiovascular disease”, affirmed Asvold. Boelaert adds that there is a scarcity of large clinical trials showing the effects of lowering substantially raised serum TSH concentrations (>10 mU/L) on blood pressure and lipid profiles. Results from such trials should inform further research assessing the consequences of reducing serum TSH concentrations that are just above or at the upper limit of the normal range. “That would be the way forward,” she concluded. Researchers in Norway have found that high normal concentrations of TSH are associated with raised blood pressure and lipid levels, but only slightly. “Differences in normal thyroid function may be associated with differences in future blood pressure and lipid levels but the strength of the association suggests that the finding may not be clinically relevant”, the authors concluded. The prospective population-based study, which had a follow-up period of 11 years, examined 9709 women and 4644 men with serum TSH levels within the reference range (0·45–4·5 mU/L) at baseline. Cross-sectional studies have shown that people with substantially raised TSH concentrations have high blood pressure and adverse lipid profiles. However, this finding is no more than an association, and causation remains unproven. Nonetheless, one possibility is that high TSH levels are an indicator of a low-functioning thyroid gland that is producing relatively low amounts of thyroxine, which raises blood pressure and lipid concentrations. “We do have thyroid hormone receptors in the heart so it is possible that subtle thyroid hormone deficiencies are linked directly to reduced thyroid hormone action in the vascular system,” suggests Kristien Boelaert (University of Birmingham, UK). “Our study found a more modest association than we expected based on cross-sectional studies involving individuals with TSH within the reference range”, said lead author Bjorn Olav Asvold. “One possible explanation could be that TSH co-varies with blood pressure and lipid levels rather than having a long-term effect.” Their study showed indications of this association, with patients' blood pressures and lipid levels increasing and decreasing in line with TSH concentrations. Perhaps a common cause is at work. Asvold suggests fat—in that leptin secreted from adipose tissue might stimulate TSH production, and high blood pressure and lipid levels often accompany adiposity. For future research, clarification of the effects of thyroid hormones on the heart will be useful. “It is important to know whether thyroid function influences the risk of cardiovascular disease”, affirmed Asvold. Boelaert adds that there is a scarcity of large clinical trials showing the effects of lowering substantially raised serum TSH concentrations (>10 mU/L) on blood pressure and lipid profiles. Results from such trials should inform further research assessing the consequences of reducing serum TSH concentrations that are just above or at the upper limit of the normal range. “That would be the way forward,” she concluded.