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Almost half of all adults in the United States have high blood pressure (hypertension). Hypertension is a major global health concern that negatively impacts general health.¹
Many factors can cause hypertension. Research has found a link between hypertension and thyroid disease. About 20 million people in the United States have some form of thyroid disease.²
Hypertension is a condition where the blood consistently exerts too much pressure on the artery walls around the body.
Blood pressure is determined by:
The volume of blood pumped by the heart
The condition of the heart valves (the structures that keep the blood flowing in the right direction)
How well the heart pumps
Size and resistance of the arteries
The causes of high blood pressure can depend on whether it is a primary or secondary condition.
Secondary hypertension makes up around 10% of all cases of high blood pressure. This type of high blood pressure is caused by another medical condition. Conversely, primary hypertension typically occurs due to lifestyle and family history rather than an underlying medical condition.³
Causes of secondary hypertension include medical conditions like kidney, cardiovascular, and hormone (such as thyroid) disorders. Two examples of thyroid disorders that can cause secondary hypertension are hyperthyroidism and hypothyroidism.
Blood pressure consists of systolic and diastolic pressure. They make up the two numbers recorded on a blood pressure measurement.
Systolic blood pressure, the top number on a blood pressure measurement, is the pressure that’s placed on the blood vessel walls when the heart contracts. Diastolic blood pressure, the bottom number on the measurement, is the pressure placed on the blood vessel walls when the heart relaxes between each heartbeat.
People with hypertension often have no recognizable symptoms. If symptoms do occur, they typically present when the hypertension is at a severe stage.
Someone with severe hypertension may experience one or more of the following symptoms:
Shortness of breath
Irregular heart rhythms
Buzzing in the ears
Nausea and vomiting
The main causes and risk factors for hypertension include:
Diet: Excessive sodium (salt) intake, high saturated and trans fat intake, and low intake of potassium-rich foods (found in leafy greens, fruits, starchy vegetables, beans, and legumes)
Excessive alcohol use
Genetics and a family history of hypertension
Gender: Men under the age of 64 are more likely to develop hypertension, while women are more likely to develop it over the age of 65
Age: The risk of hypertension increases with age
Having obesity or being overweight
Race: In the United States, African-Americans are more likely to have hypertension
Certain medical conditions, such as chronic kidney disease, diabetes, high cholesterol, and thyroid problems
Some medications and supplements, including over-the-counter drugs (such as aspirin and ibuprofen), some antidepressants (such as monoamine oxidase inhibitors, fluoxetine, and tricyclic antidepressants), birth control, and some stimulants such as methylphenidate
The thyroid is a small, butterfly-shaped gland found at the base of the neck. It is located below Adam’s apple and just above the collarbone. The thyroid gland produces and releases two thyroid hormones — thyroxine (T4) and triiodothyronine (T3).
Thyroid hormones help to regulate and control many aspects of growth, metabolism, and development. They are important for the healthy functioning of many organs and body processes, including the heart and blood pressure.
Two factors determine blood pressure:
Cardiac output (the amount of blood the heart pumps in one minute)
Thyroid hormones regulate blood pressure by influencing cardiac output and peripheral resistance. For example, the thyroid hormone T3 relaxes the arteries and keeps them dilated, which reduces peripheral resistance and increases cardiac output.
This happens because thyroid hormones target key regulators of resistance in the blood vessels. Thyroid hormones also influence blood pressure more indirectly by regulating kidney function.
Research has found a link between thyroid disorders and hypertension. How this happens depends on the specific thyroid disorder, but the disease is generally known to affect the functions of the heart and blood vessels in the body.
Anemia is when there aren’t enough healthy red blood cells in the bloodstream. Research has found that people with hyperthyroidism and hypothyroidism are more likely to have anemia. But it’s not known for sure whether there could be a direct cause-and-effect relationship between the two disorders.⁴
Thyroid hormones must be within an optimal range for organs and body processes to function correctly. When they aren’t within a normal range, problems can occur.
The most common thyroid problems include:
Hypothyroidism is a condition where the thyroid is underactive and doesn’t produce enough thyroid hormones.
Hypothyroidism can be caused by:
Autoimmune diseases such as Hashimoto’s thyroiditis
Treatment for hyperthyroidism with antithyroid drugs
Thyroid cancer or growths (nodules) on the gland
Hyperthyroidism is a condition where the thyroid is overactive and produces too many thyroid hormones.
Hyperthyroidism can be caused by:
Autoimmune diseases such as Graves’ disease
Excessive iodine exposure
Viruses, which can cause inflammation and subacute thyroiditis
Other thyroid problems include:
Multinodular goiter: This is when multiple growths (nodules) appear on the thyroid gland. Most of the time, multinodular growths are not cancerous. However, they can still cause thyroid problems.
Hypertension can occur in both subclinical and overt hyperthyroidism and hypothyroidism.
Usually, hypertension that is caused by a thyroid disorder is mild.
Hypothyroidism can cause hypertension by:
Weakening the muscles of the heart
Increasing the peripheral resistance
Making the arteries stiffer and less elastic
Making the heart less efficient when it beats and pumps blood around the body
Increasing sympathetic nervous system activity⁵
Reducing the glomerular filtration rate (how well the kidneys filter fluid)
In hypothyroidism, diastolic blood pressure is more likely to be increased than systolic blood pressure.
Hyperthyroidism and the increased production of thyroid hormones can cause hypertension by:
Causing the heart to work harder
Increasing the heart rate and cardiac output
Improving thyroid function is often the main goal when hypertension occurs due to a thyroid disorder. However, there are steps you can take to try to manage your blood pressure while you are treating the thyroid disorder.
In these circumstances, lifestyle changes are unlikely to be enough to reduce blood pressure on their own. However, building healthy habits can help to keep your blood pressure and heart as healthy as possible.
Some potential lifestyle changes and healthy habits that someone with hypertension might make include:
Physical activity: For maximum benefits, it is recommended to get at least 150 minutes of physical activity each week.
Reduce alcohol intake
Diet: People with hypertension should try to reduce their sodium intake (salty foods) and concentrate on eating unsaturated fats rather than saturated fats. The Dietary Approaches to Stop Hypertension diet is recommended for its focus on reducing hypertension and promoting heart health.
Maintain a healthy weight: It’s best to try to maintain a healthy weight and lose weight if you are overweight.
Manage daily stressors
People with high blood pressure, regardless of the cause, should have their blood pressure measured frequently. Fortunately, measuring your blood pressure is simple, fast, and non-invasive.
The American College of Cardiology and the American Heart Association provides the following guidelines for classifying blood pressure as normal, elevated, or hypertensive:
Normal: Below 120/80 millimeters of mercury (mm Hg)
Elevated: Above 120/80-129/80mm Hg
Stage I hypertension: 130-139/80-89mm Hg
Stage II hypertension: 140/90mm Hg
Because high blood pressure often presents with no symptoms, people usually don’t know they have it until a doctor measures their blood pressure. To determine whether thyroid problems are the cause of hypertension, blood tests can be used to detect thyroid-stimulating hormone (TSH) levels and thyroid hormone levels.
The following guidelines can be used:
Normal T4 levels are between 5.0-11.0 ug/dL
Normal T3 levels are between 100-200 ng/dL
Normal TSH levels are between 0.40-4.50 mIU/mL
When thyroid hormone levels are low and TSH is high, hypothyroidism may be the cause. When thyroid hormone levels are high and TSH is low, hyperthyroidism may be the cause.
Uncontrolled hypertension can damage the heart and blood vessels, leading to heart disease and the following complications:
Heart attack: Occurs when the blood supply to the heart becomes blocked and heart muscle cells die due to a lack of oxygen
Chest pain: Angina
Heart failure: Occurs when the heart can’t pump enough blood to meet the body's demands
Arrhythmia: An irregular heartbeat
Hypercoagulopathy: When the blood clots too much
Strokes: Occur if the arteries that supply blood and oxygen to the brain become blocked and burst
Chronic kidney disease and kidney failure, if the blood vessels in the kidney weaken
Difficulty with memory or understanding
Aneurysm: Occurs when a blood vessel becomes weak and bulges
Atherosclerosis: The hardening and thickening of arteries
Secondary hypertension can cause whatever medical condition is causing it to worsen. This means if hyperthyroidism or hypothyroidism is the cause, hypertension might worsen these conditions.
For people with secondary hypertension, it’s important to treat the medical condition that’s responsible for causing it. By correcting thyroid function, normal blood pressure can often be restored.
Hyperthyroidism can be treated with antithyroid medications, which help to reduce thyroid hormone levels by preventing the thyroid gland from making too many hormones. Methimazole (Tapazole) is the primary antithyroid medication used in the United States.
Hyperthyroidism can also be treated with radioactive iodine, which is absorbed by the thyroid, causing it to shrink. Another treatment option is thyroid surgery, which removes all or part of the thyroid gland.
Hypothyroidism is treated with thyroid replacement medications. Levothyroxine (Synthroid, Levoxyl) is the main thyroid replacement hormone that works to increase the thyroid hormone levels in the body.
Secondary hypertension itself may not respond to blood pressure medications, as they don’t affect the production of thyroid hormones. However, beta-blockers (a type of blood pressure medication) may still be helpful if the normalization of thyroid function after using thyroid medications doesn’t resolve the high blood pressure.
Beta-blockers such as propranolol (Inderal) can also help manage the cardiovascular-related symptoms of hyperthyroidism, such as a fast, irregular heart rhythm and heart palpitations.
Hyperthyroidism and hypothyroidism are two thyroid disorders that have been linked to hypertension. Fortunately, adequate treatment can not only treat the underlying thyroid disorder but can also indirectly treat hypertension.
If you are concerned about your thyroid function or blood pressure, it’s a good idea to see your doctor. They can measure your blood pressure and order other blood tests, so you’ll receive a diagnosis and begin effective treatment as soon as possible.
Hyperthyroidism and hypothyroidism are two thyroid problems that can both cause high blood pressure, but the mechanism of how this happens differs. Hyperthyroidism causes high blood pressure by making the heart beat faster and work harder due to the increase in thyroid hormones. Hypothyroidism is thought to cause high blood pressure by weakening the heart muscles and increasing resistance in the blood vessels around the body.
Thyroid problems, most often an underactive thyroid (hypothyroidism), can cause unexplained weight gain.
The potential early warning signs depend on what the exact thyroid problem is. Early signs may include unexpected weight gain or loss, resistance to heat or cold, changes in bowel movements (diarrhea or constipation), increased or decreased heart rate, and mood changes.
People with hyperthyroidism are more likely to lose weight than gain weight because hyperthyroidism often causes an increase in metabolism. Although less common, someone with hyperthyroidism can gain weight, as an increased appetite is a possible symptom of hyperthyroidism.
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Hypertension | World Health Organization
Know your risk factors for high blood pressure | Heart Attack and Stroke Symptoms
Know your risk for high blood pressure | Centers for Disease Control and Prevention
Thyroid hormone: How it affects your heart | Harvard Health Publishing
High blood pressure symptoms and causes | Centers for Disease Control and Prevention
Beating high blood pressure with food | Harvard Health Publishing
The link between thyroid disorder and hypertension | Heart and Vascular Institute