Widely used thyroid pill may be linked to bone loss

A widely used pill for treating an underactive thyroid may be associated with bone loss, according to a study being presented next week at the annual meeting of the Radiological Society of North America in Chicago.

The drug, levothyroxine, is a synthetic version of the hormone produced by the thyroid gland. About 23 million Americans, some 7% of the U.S. population, take generic levothyroxine or the branded version sold by AbbVie as Synthroid, daily.

In a study of nearly 450 older adults, including 81 taking levothyroxine, the drug was associated with greater loss of total body bone mass and bone density over a median follow-up of 6.3 years.

This was true even though users' thyroid hormone levels were in the normal range.

“Our study suggests that even when following current guidelines, levothyroxine use appears to be associated with greater bone loss in older adults,” Dr. Shadpour Demehri of Johns Hopkins University School of Medicine in Baltimore, who worked on the study, said in a statement.

Co-author Dr. Jennifer Mammen, also of Johns Hopkins, advises that adults taking levothyroxine should discuss their treatment with their healthcare provider.

“A risk-benefit assessment should be conducted, weighing the strength of the indications for treatment against the potential adverse effects,” she said.

Gut bacteria affect benefit of cancer drug

The effectiveness of the oral breast cancer drug tamoxifen depends in part on the “healthy” bacteria living in the intestines, experiments in mice have shown.

“While tamoxifen is a common and important treatment for preventing breast cancer recurrence, nearly 50% of patients don’t respond well to it,” study leader Yasmine Alam, of the University of California, Irvine, said in a statement.

Tamoxifen passes through the stomach and into the intestines, where it is absorbed into the bloodstream. Once in the blood, tamoxifen travels to the liver, where it is changed into a form that is more effective at fighting breast cancer.

However, a sugar molecule can sometimes become attached to it, and the drug can only get out of the intestine if the sugar is removed.

Certain enzymes produced by gut bacteria, called beta-glucuronidases, can digest the sugar so the tamoxifen can go on to fight breast cancer, researchers said in a report published on Monday in mBio.

A particular type of bacteria, Bacteroides fragilis, was strongly linked to the ability of these enzymes to affect tamoxifen levels in the blood in a positive way, the researchers found.

In the future, doctors may test patients' stool to check for certain bacteria in the gut that might help predict whether tamoxifen will work for them.

Strategies for reducing exposure to wildfire smoke pollution are available from the U.S. Environmental Protection Agency.