Levothyroxine, a drug used to treat hypothyroidism, is prescribed for 23 million Americans every year.
In Clinical Chemistry, a Yale scientist warns that up to 90% of it might be completely unnecessary and based on a common cause of misdiagnosis.
When more than 10% of a country’s adult population is put on a drug, scientists tend to be concerned. This is the fact that stimulated the recent scientific letter.
Joe M. El-Khoury, a chemist at Yale, thinks that most hypothyroidism cases are misdiagnosed based on seasonal variations in one of the hormones tested.
He referenced a Japanese study involving more than 7,000 healthy individuals that demonstrated that levels of thyroid-stimulating hormone (TSH) varied significantly throughout the year.
The study, published in the Journal of the Endocrine Society in 2022, showed that TSH levels peaked during the winter (January to February) and dipped to their lowest in the summer (June to August).
Meanwhile, free thyroxine (FT4) levels remained relatively constant throughout the year.
When TSH tests high and thyroxine tests normal, doctors assume that a patient has subclinical hypothyroidism. They take it as a sign that the thyroid is underactive and needs a lot of stimulation to be able to produce its hormones.
However, if it is true that TSH is naturally high during the winter, then everyone diagnosed during those months is incorrectly assumed to have an underactive thyroid and is actually healthy.
El-Khoury pointed out that the standard reference ranges used by laboratories do not account for these seasonal fluctuations, leading to unnecessary prescriptions of levothyroxine for healthy individuals. Overmedication, especially in older people, can cause great harm.
A US study conducted in 2021 found that 90% of these prescriptions were unnecessary, and El-Khoury believes that this seasonal TSH variation could explain up to half of the unnecessary prescriptions.
In fact, apart from seasonal variation, studies suggest that there are other factors, such as pregnancy status, co-existing health conditions, age, and even certain medications or supplements, that can affect whether TSH tests high or normal.
The risks of taking too much levothyroxine are significant. It can increase one’s heart rate and blood pressure, raise one’s body temperature, and ruin one’s sleep. In addition, it causes depression, anxiety, diarrhea, fatigue, and weight loss.
These are major health problems for a relatively healthy adult, but some of them can be deadly in a person who is unhealthy or elderly.
Therefore, don’t let your doctor talk you into a hypothyroidism diagnosis that might not be accurate, and keep the serious side effects of the drug in mind before you receive an unnecessary prescription.