Antibiotic exposure during a critical window of early development alters the gut microbes and permanently reprograms the body’s metabolism, which may increase one’s susceptibility to obesity, according to a new study published in the journal Cell.

Martin Blaser, MD, of the NYU School of Medicine, and colleagues gave water with low doses of penicillin to three groups of mice. One group received antibiotics in the womb during the last week of pregnancy and continued the medication throughout life. The second group received the same dose after waning and continued throughout life, and the third group received no antibiotics. They found that mice given lifelong low doses of penicillin starting in the last week of pregnancy or during nursing were more susceptible to obesity and metabolic abnormalities than mice exposed to the antibiotic later in life.

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Researchers noted that more evidence is needed before concluding whether antibiotics lead to obesity in humans, and that physicians should not be hindered in prescribing antibiotics to children when necessary.

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