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Widely used thyroid pill may be linked to bone loss

About 23 million Americans take generic levothyroxine or the branded version sold by AbbVie as Synthroid, daily

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.

It could also be worthwhile to determine which bacteria interact with the drug and to identify foods that support the growth of these bacteria to provide dietary advice to patients prescribed tamoxifen, the researchers said.

Wildfire smoke linked with dementia risk

Higher long-term exposure to wildfire smoke was associated with significantly higher odds of developing dementia, according to a large California study.

Researchers analyzed data collected between 2008 and 2019 from 1.2 million residents of southern California, aged 60 and older, all of whom were free from dementia at the start of the study. They estimated each person’s long-term exposure to fine particulate matter (PM2.5) air pollution as a three-year rolling average.

For every 1 microgram per cubic meter increase in the concentration of wildfire PM2.5, the odds of a dementia diagnosis increased by 18%, according to a report published on Monday in JAMA Neurology.

Exposure to non-wildfire PM2.5 also increased a person’s risk of dementia, but to a much lesser degree, the study found.

“One microgram per meter cubed might sound fairly small, but we have to think about how people are exposed to wildfire smoke,” study leader Joan Casey of the University of Washington in Seattle said in a statement.

On most days, people aren’t exposed to wildfire smoke at all, she pointed out.

“So this might represent a few days of exposure at a concentration of something like 300 (micrograms per cubic meter), where the Air Quality Index is over 200 in someone’s community... it’s actually a few really severe wildfire smoke days that might translate into increased risk.”

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