More than 15 percent of older Americans take thyroid hormone, and its use has risen—mostly among people with subclinical hypothyroidism, defined as an elevated blood level of thyroid stimulating hormone (TSH) but a normal level of the thyroid hormone thyroxine (T4).
People who experience fatigue, weight gain, hair loss, depression, and “brain fog” may attribute these and other vague symptoms to subclinical hypothyroidism, though such symptoms could be due to a range of other conditions. Now two papers have suggested that many people with subclinical hypothyroidism may be taking thyroid hormone unnecessarily, particularly older adults.
In the first paper, published in BMJ in May 2019, an international expert panel issued a “strong recommendation” against routinely prescribing thyroid hormone for people with subclinical hypothyroidism. The recommendation was based on an analysis of 21 clinical trials with nearly 2,200 participants, which found that for people with subclinical hypothyroidism, the hormone (usually levothyroxine, a synthetic version of T4) consistently demonstrates “no clinically relevant benefits for quality of life or thyroid-related symptoms, including depressive symptoms, fatigue, and body mass index.”
The recommendation doesn’t apply to certain groups, including people with a “very high” TSH (which the panel defined as above 20) but a normal T4 level. (This is more conservative than other guidelines, which tend to advise treating TSH levels over 10.) People with severe symptoms or who are younger than 30 may also still benefit from treatment, the panel said.
The second paper, a review in the Journal of the American Medical Association (JAMA) in July 2019, reached a similar conclusion, with the authors noting that TSH levels often rise with age even though nothing is wrong with the thyroid. “This phenomenon has likely led to an overestimation of the true prevalence of subclinical hypothyroidism in persons older than 70 years,” the authors wrote. They added that there is no evidence that levothyroxine therapy for subclinical hypothyroidism is beneficial in people 65 and older.
Like the earlier paper, the JAMA review concluded that most people with subclinical hypothyroidism should be monitored by their doctors, rather than treated with levothyroxine. People for whom treatment “might be indicated” include those with TSH levels of 10 or higher and young or middle-aged people who are having symptoms consistent with mild hypothyroidism.
What you should do
If you are taking levothyroxine, you should have your thyroid hormone levels tested regularly to make sure the dosage isn’t too high (which in effect can cause hyperthyroidism). And don’t stop taking the medication without medical advice. Note that neither the BMJ nor the JAMA recommendation applies to pregnant women, who are usually treated with levothyroxine for subclinical hypothyroidism because of the risks that an underactive thyroid pose to the fetus, including premature birth and miscarriage.
This article first appeared in the UC Berkeley Wellness Letter.
Also see The Cholesterol-Thyroid Connection.