Can hypothyroidism (underactive thyroid) cause hypertension (high blood pressure) in an adult patient?

Can Hypothyroidism Cause Hypertension?

Yes, hypothyroidism is a well-established cause of hypertension, particularly diastolic hypertension, and treatment with levothyroxine can normalize blood pressure in many patients. 1

Mechanism and Prevalence

Hypothyroidism causes hypertension through several pathophysiologic mechanisms:

• Systemic vascular resistance increases by up to 50% in hypothyroid patients, leading to elevated blood pressure, particularly diastolic hypertension with narrowed pulse pressure 1
• Mild diastolic hypertension is common due to this increased peripheral resistance 1, 2
• The prevalence of hypothyroidism among hypertensive patients ranges from 1.2% to 3.6% in referred populations 3

Clinical Recognition

The American College of Cardiology explicitly recommends:

• Measuring thyroid-stimulating hormone (TSH) in all newly diagnosed hypertensive patients as part of basic laboratory testing, as both hypothyroidism and hyperthyroidism are remediable causes of hypertension 1

Key clinical features that should raise suspicion include:

• Bradycardia (slow heart rate) 2
• Narrowed pulse pressure 2
• Coarse skin, periorbital puffiness, delayed ankle reflex 2
• Fatigue, weight gain, constipation 2

Reversibility with Treatment

Treatment with levothyroxine can normalize blood pressure in a substantial proportion of patients:

• In one study, 40% of thyrotoxic patients developed diastolic hypertension >90 mmHg after radioiodine-induced hypothyroidism, and restoration of euthyroidism normalized blood pressure in 56% of these hypertensive patients 3
• Among 25 hypothyroid hypertensive patients, 32% achieved blood pressure <90 mmHg diastolic after thyroid hormone replacement alone, without antihypertensive medications 3
• Complete normalization of blood pressure occurred in 50% of patients with combined hypothyroidism and hypertension after levothyroxine therapy 4
• Blood pressure typically decreases from levels like 172/112 mmHg to 140/84 mmHg with thyroxine treatment 5

Important Caveats

Not all hypertension in hypothyroid patients is reversible:

• Approximately 50% of patients with hypothyroidism and hypertension will have sustained hypertension despite adequate thyroid hormone replacement 4
• Increased aortic stiffness is the primary mechanism for persistent hypertension after thyroid replacement; patients with higher aortic stiffness index are less likely to achieve blood pressure normalization with levothyroxine alone 4
• These patients with persistent hypertension may require additional antihypertensive therapy (such as calcium channel blockers) alongside thyroid replacement 4

Role in Heart Failure

The American College of Cardiology/American Heart Association guidelines explicitly list:

• Hypothyroidism as a common precipitant of acute decompensated heart failure, and restoration of normal thyroid function may reverse abnormal cardiovascular function 6, 1
• Hypothyroidism should be suspected in patients treated with amiodarone who develop heart failure decompensation 6

Clinical Algorithm

For any adult patient with newly diagnosed hypertension:

1. Measure TSH as part of initial laboratory evaluation 1
2. If TSH is elevated (>6.5 mU/L) with low or normal free T4, diagnose hypothyroidism 6
3. Initiate levothyroxine replacement therapy at low doses, especially in patients with cardiac disease 1
4. Reassess blood pressure after achieving euthyroidism (typically 6-8 weeks after starting treatment) 3
5. If hypertension persists despite normalized thyroid function, consider increased aortic stiffness as the mechanism and add conventional antihypertensive therapy 4

Hypertension in hypothyroid patients only requires further evaluation if it persists after adequate treatment with thyroxine. 5