Morbid obesity reduces the effectiveness of levothyroxine for patients with hypothyroidism

Due to the dampening effect that a higher body mass index (BMI) can have on the body's absorption of a thyroid hormone replacement called levothyroxine (LT4), a group of Greek researchers recently investigated how morbid obesity might change the uptake of this drug in patients with hypothyroidism.

The team, whose members hail from Greece's University Hospital of Patras, found that it took longer for orally administered LT4 to reach its maximum blood concentration in individuals whose BMIs were over 40, compared to participants in a healthy weight range.

Furthermore, the maximum registered blood concentration of the replacement hormone was lower among the morbidly obese than it was for lean individuals.



The study's findings may affect hypothyroidism research, though none of the participants suffered from the condition, which consists of having low levels of thyroid hormones in the body.



The University of Maryland Medical Center states that hypothyroidism can result in chronic fatigue, dry skin, brittle hair, muscle aches and weight gain.

Previous studies have addressed the potential for the condition to contribute to obesity. A 2008 report published in the Saudi Medical Journal found that 46 percent of patients with diagnosed hypothyroidism were obese, and 34 percent of those with a subclinical level of the condition also suffered from obesity.

With this in mind, the Greek team monitored the thyroid hormone levels of severely obese people before, during and up to four hours after the administration of LT4.

Scientists found that morbidly obese participants had higher baseline levels of natural thyroid hormones prior to taking the synthetic version. However, their thyroid hormone levels rose to a lower peak after being given LT4, which researchers partially attributed to the greater volume of blood in patients with high BMIs.

The study concluded that severely obese individuals with hypothyroidism may require larger doses of LT4 to effectively treat the disorder, which affects 5 percent of Americans, according to the National Institute of Diabetes and Digestive and Kidney Diseases.
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