Can hypothyroidism (underactive thyroid) cause hypertension (High Blood Pressure) in adults?

Hypothyroidism Can Cause Hypertension

Yes, hypothyroidism is a recognized cause of secondary hypertension, particularly diastolic hypertension, and should be screened for in all newly diagnosed hypertensive patients. 1

Mechanism and Prevalence

Hypothyroidism causes hypertension through several pathophysiologic mechanisms:

• Increased systemic vascular resistance by as much as 50%, which is the primary driver of diastolic blood pressure elevation 1
• Increased aortic stiffness, which contributes to sustained hypertension even after thyroid hormone replacement in some patients 2
• Volume-dependent mechanism with low plasma renin activity, suggesting sodium retention as a contributing factor 3, 4

The prevalence is clinically significant: hypothyroidism was found in 3.6% of consecutive hypertensive patients referred for evaluation, making it a relatively common cause of secondary hypertension 5

Clinical Evidence for Blood Pressure Normalization

The relationship between hypothyroidism and hypertension is well-established and often reversible:

• In one study of 40 thyrotoxic patients made hypothyroid by radioiodine therapy, 40% developed diastolic hypertension (BP >90 mmHg), which improved significantly with thyroxine replacement 5
• Among hypothyroid hypertensive patients treated with levothyroxine, blood pressure normalized completely in approximately 32-50% of cases 2, 5, 3
• Six patients with hypothyroidism and hypertension demonstrated complete normalization of blood pressure (from 172/112 to 140/84 mmHg) with thyroxine treatment alone 3

Screening Recommendations

The American College of Cardiology recommends measuring TSH in all newly diagnosed hypertensive patients as part of basic laboratory testing, as both hypothyroidism and hyperthyroidism are remediable causes of hypertension 1

This screening approach is justified because:

• Hypothyroidism is present in 1.2% of referred hypertensive patients whose hypertension completely resolves with thyroid hormone replacement 5
• Treatment with levothyroxine can normalize blood pressure in patients with hypothyroid-induced hypertension 1

Treatment Approach and Outcomes

When hypothyroidism is identified in hypertensive patients:

• Initiate levothyroxine replacement therapy as the primary intervention 1
• Monitor blood pressure response after achieving euthyroidism before adding or continuing antihypertensive medications 5, 3
• Approximately 50% of patients will have persistent hypertension despite thyroid hormone normalization, likely due to irreversible increases in aortic stiffness 2
• For those with sustained hypertension after levothyroxine, standard antihypertensive therapy (such as calcium channel blockers) effectively reduces both blood pressure and aortic stiffness 2

Important Clinical Caveats

Aortic stiffness predicts treatment response: Patients with higher baseline aortic stiffness are less likely to achieve complete blood pressure normalization with levothyroxine alone (odds ratio 1.99) 2. This explains why some patients require continued antihypertensive therapy even after achieving euthyroidism.

Avoid premature antihypertensive therapy: Hypertension in hypothyroid patients only requires additional antihypertensive evaluation if it persists after adequate treatment with thyroxine 3. Starting antihypertensive medications before correcting hypothyroidism may result in unnecessary lifelong therapy.

Cardiovascular complications: Untreated hypothyroidism contributes not only to hypertension but also to dyslipidemia, heart failure, and increased cardiovascular mortality 6, 7. The combination of diastolic hypertension with bradycardia, elevated LDL cholesterol, and fatigue should prompt thyroid function testing.