Hypothyroidism and Heart Health

When it comes to the health of your heart, thyroid hormones play an important role in normal heart function, and hypothyroidism has profound cardiovascular effects. The thyroid’s job is to make thyroid hormones (T4 & T3), which are secreted into the blood and then carried to every tissue in the body. Thyroid hormones help the body use energy, stay warm and keep the brain, heart, muscles, and other organs working as they should. Here are some ways your thyroid gland relates to your heart. 

Thyroid and Cardiac Output

Hypothyroidism decreases cardiac output.

Thyroid hormone influences the force and speed of your heartbeat and your blood pressure. When the thyroid is healthy, the heart’s output is healthy, which means the body can push more blood out of the heart in a single beat, so circulation improves (left ventricle function).

Insufficient thyroid hormone (hypothyroid) decreases cardiac output and slows your heart rate. A decrease in cardiac output results in arteries becoming stiffer (aka: less elastic) and blood pressure rises in order to circulate blood around the body.

It may also cause an increase in fluid around the heart, and heart failure. Aside from regulating your thyroid hormone levels, here are additional lifestyle and nutrition intervention tips for hear failure.

Thyroid and Blood Pressure

In a hypothyroid state, the heart’s ability to contract is affected, along with impaired cardiac muscle relaxation. There’s an increase in diastolic blood pressure, and the atrial chambers of the heart are negatively affected.

The Thyroid and Cholesterol Metabolism

Optimal thyroid function is important in healthy cholesterol metabolism. A hypothyroid state leads to elevated total cholesterol, LDL cholesterol (bad cholesterol), and apolipoprotein B. There’s also a reduction in the enzymes that break down cholesterol in the body, resulting in less cholesterol clearance.

Here’s an interesting tidbit…doctors used to look at a person’s cholesterol levels to gauge how their thyroid was functioning – higher cholesterol levels were associated with lower thyroid function. Medicine has since evolved and now we’re able to measure Thyroid Stimulating Hormone (TSH), free T3 and free T4 to determine thyroid function.

Thyroid and Sugar Metabolism

Hypothyroid can be associated with a decrease in insulin sensitivity due to downregulation of glucose transporters and direct effects on insulin secretion and clearance. Here’s more about the connection between blood sugar, insulin and heart disease. 

When it comes to stress, the thyroid will become less efficient when it’s over responding to stress. When stress hormones elevate, it causes the blood sugar to fluctuate more quickly and to over-release insulin.

Thyroid and Lean Muscle Mass

Your body fat levels are thyroid dependent. A person with a healthy functioning thyroid will be able to more easily maintain a healthy body fat percentage vs. a slow functioning thyroid will store fat more easily. T3 is involved in thermogenesis (the burning of fat and releasing fat as heat). The thyroid hormones T3 activate brown fat, which is typically stored along the upper back and upper chest. Brown fat burns white fat and releases it as heat. This is one reason, along with poor circulation, people with poor thyroid function are cold.

The Effects of Xenoestrogens and Toxic Metals on Thyroid

Believe it or not, the thyroid is affected by toxins such as pesticides (organochlorines) and PCBs, which are xenoestrogens. They lower your T3 levels, consequently slowing your resting metabolic rate and inhibiting your fat-burning ability. Get your liver functioning well by eating the right nutrients to support Phase 1 and Phase 2 detoxification. 

Xenoestrogens can act on the estrogen, androgen, and thyroid hormone receptors, and can then bind to and activate different hormone receptors, and by doing this can mimic the natural hormone’s action. So if xenoestrogens aren’t being detoxified effectively, they have estrogen-like effects on the body. Women (and men) who are estrogen dominant don’t make the conversion from T4 to active T3 very well.

Toxic metals interfere with T4 production, blocks conversion of T4 to T3, negatively impacts the receptor site. Aluminum is toxic to the pituitary and thyroid both. Link to HMA.

Labs to Test for Thyroid Function

Thyroid Stimulating Hormone (TSH)

TSH is produced by the pituitary gland and tells the thyroid to do more or do less when it comes to producing T3 and T4. When thyroid hormone levels decrease in the blood, the pituitary gland produces more TSH in response to TRH stimulation. TSH in turn stimulates the thyroid to produce and release more T4 and T3.

Testing only TSH is fine if the signaling is working well, but if it’s not, TSH isn’t the whole thyroid picture.

Ideal value: 0.5-1.5 IU/mL

Free T4  (the inactive form)

The thyroid makes T4 and it gets converted to T3, the active form. T4 effects brain, lungs, and heart.

Ideal value: 1.3-1.6 ng/dL

Free T3 (the active form)

T3 stimulates the contraction of the left heart ventricle. A healthy cardiac output indicates optimal left ventricle function.

T4 effects brain, lungs, and heart. T3 effects those and everything else.

Ideal value: 3.5 ng/dL or higher (a lab range is 2.3-4.2)

If you suspect you have suboptimal thyroid function, seek out a functional medicine doctor to help you get it regulated. If you've been turned down by conventional doctors and told your thyroid is "fine" but you don't feel fine, never lose hope. Take a proactive approach to find a functionally trained doctor. It worked for me!

Kelly Harrington, MS, RDN

Registered Dietitian for Healthy Goods



Harvard Medical School. Thyroid hormone: How it affects your heart. Feb. 2015. 

2013 ETA Guideline: Management of Subclinical Hypothyroidism. Pearce SH, Brabant G, Duntas LH, Monzani F, Peeters RP, Razvi S, Wemeau JL. Eur Thyroid J. 2013 Dec; 2(4):215-28. 

Pelletier C, Imbeault P, Tremblay A. Energy balance and pollution by organochlorines and polychlorinated biphenyls. Obes Rev. 2003 Feb; 4( 1): 17– 24. Review.


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