Treating mild hypothyroidism: Benefits still uncertain – Harvard Health Blog

Your thyroid, a tiny, butterfly-shaped gland located in front of your windpipe (trachea) and below your voice box (larynx) can have a profound impact on your health and well-being. Throughout life, your thyroid is constantly producing hormones that influence your metabolism. These hormones affect your mood, energy, body temperature, weight, heart, and more.

A brief overview of hypothyroidism

Your thyroid produces two kinds of thyroid hormones: T4, or thyroxine, and T3, or triiodothyronine. These hormones influence every cell, tissue, and organ in your body, from your muscles, bones, and skin to your digestive tract, brain, and heart, by controlling how fast and efficiently cells convert nutrients into energy — a chemical activity known as metabolism.

The thyroid gland is under the influence of the pituitary gland. No larger than a pea and located at the base of the brain, the pituitary gland controls your thyroid’s production of thyroid hormone by releasing thyroid stimulating hormone (TSH).

TSH levels in your bloodstream rise or fall depending on whether there is enough thyroid hormone made to meet your body’s needs. Higher levels of TSH prompt the thyroid to produce more thyroid hormone, while lower levels signal the thyroid to produce less.

Hypothyroidism occurs when the thyroid fails to produce enough thyroid hormone to meet the body’s needs, thereby slowing metabolism. In someone with overt hypothyroidism, thyroid hormone levels are below normal and TSH levels are well above the normal range.

What is mild hypothyroidism?

Subclinical, or mild, hypothyroidism doesn’t meet the standard definition of hypothyroidism. In mild hypothyroidism, you may or may not have symptoms and your levels of T4 and T3 are normal, but your TSH levels are slightly elevated. Mild hypothyroidism is diagnosed by a blood test.

More than 10 million adults in the US have hypothyroidism, the vast majority of which is subclinical.

What are the risks of leaving mild hypothyroidism untreated?

Whether or not to treat mild hypothyroidism is a subject that has been studied and debated for years. What worries doctors most about mild hypothyroidism is the potential link between untreated mild hypothyroidism and coronary artery disease. Results of research on whether subclinical thyroid disease causes heart problems have been conflicting. The condition has been associated with heart and blood vessel abnormalities, and studies indicate that treating mild hypothyroidism can improve various markers of heart structure and function.

However, a recent study published in the Journal of the American Medical Association may give doctors pause. The researchers studied people with mild hypothyroidism who had also had a heart attack. They treated one group of these patients for their mild hypothyroidism, and left the condition untreated in the other group. The study showed that those treated for mild hypothyroidism did not have better heart function than those who were not treated.

What are the downsides of treating mild hypothyroidism?

When mild hypothyroidism is treated, levothyroxine (T4) is the treatment of choice.

A 2017 trial published in The New England Journal of Medicine found that treating people ages 65 and older for mild hypothyroidism doesn’t have much of a benefit. The authors found no real differences in symptoms between participants who received levothyroxine and those who got a placebo. The authors say many older adults revert to normal thyroid function on their own, without treatment. A follow-up study recently published in the Annals of Internal Medicine analyzed data from patients enrolled in the 2017 NEJM study, and determined that even those with the greatest number of symptoms did not benefit.

In addition to the possibility that the treatment may not offer any benefit, there are other reasons for caution. Overtreatment — prescribing thyroid medication to someone with subclinical disease who may not need treatment, or giving excessive thyroid medication — comes with serious risks, particularly thyrotoxicosis, the presence of too much thyroid hormone in the body. This happens frequently; estimates suggest 20% or more of those treated with thyroid hormone experience thyrotoxicosis. Long-term complications of even mild thyrotoxicosis can include heart problems and bone loss.

Considering the risks and benefits of treatment

If you are weighing the pros and cons of treatment for hypothyroidism, discuss the following questions with your doctor:

• How might I benefit from treatment? Could it treat my symptoms? Prevent heart disease? Help me conceive?
• What are the risks of treatment?
• How will we know if treatment is working, and how long will it take to determine this?
• For how long will I need to continue treatment?

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