Children given antibiotics gain weight more quickly than those who don’t take the medicines, and their weight gain can be cumulative and progressive, new research shows.

The study, which tracked nearly 164,000 children in Pennsylvania, concluded that healthy youngsters at age 15 who had been prescribed antibiotics seven or more times in their childhood weighed about 3 pounds more than those who didn’t take these medicines.

“Antibiotics at any age contribute to weight gain,” said Brian S. Schwartz, a physician and epidemiologist at the Johns Hopkins Bloomberg School of Public Health and lead author of the study. The research was published Wednesday in the International Journal of Obesity.

There is growing evidence linking antibiotics to weight gain. Farmers routinely put sub-therapeutic doses of antibiotics in feed to promote growth in animals.

Studies have suggested that antibiotics given to children at age 1 or 2 years contribute to increased weight, because reason may be that the the medicines kill off certain bacteria in the gut and leave behind others that break down food differently. That may cause an increase in the calories of the nutrients absorbed.

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