There is a growing body of evidence that excessive exposure to antibiotics has an effect on longer-term health problems. Antibiotics as a treatment are becoming less effective, as the bacteria they were designed to treat develop resistance. But the drugs are also changing how our bodies act - particularly in developing children - and the effects are potentially very unhealthy, writes Time.
In the largest and longest study yet looking at the potential correlation between antibiotic exposure and body mass index (BMI), researchers found that the number of doses and the length of time children were exposed to antibiotics had an adverse effect on their weight in the future. Children that endured more doses and were exposed to antibiotics the longest were shown to retain more weight and to also gain more weight over time.
A research team, led by Brian Schwartz, professor of environmental health sciences at the Johns Hopkins Bloomberg School of Public Health, studied the electronic health records of 142,824 children between the ages of three and 18 years. They grouped the antibiotic prescriptions dependent on whether these had an effect on BMI and whether this was temporary, reversible or whether the weight had been lost after one year - or if the weight had remained.
The researchers found that children given any prescription for antibiotics in the past year before their BMI had been measured - led to an increase in weight - but the children soon lost this weight after ceasing to take the drugs. However, when researchers did a comparison with children who had not taken antibiotics - they found the children who had taken the antibiotics were more likely to gain weight - and not lose it. These children were also more likely to gain more weight by the time they had reached 18 years of age.
"The more antibiotics you get, the stronger the effect," says Schwartz. "And this effect seems to get larger as you get older."
The researchers found that antibiotic use accounted for 1.6 pounds to 3.3 pounds of weight increases during the childhood years.
According to Schwartz, antibiotics are likely to have this effect on weight because of its interaction with the microbiome (bacteria living in the gut). Growing evidence suggests that altering the makeup "good" bacteria in the gut, which aid the digestion process and maintain immune system and intestinal tract health - could also affect how the body gains weight. Antibiotics could be harsh enough to kill the existing gut bacteria - repopulating the gut with bacteria that is less effective, which could explain the effects on weight. The link between longer exposure to antibiotics and increased weight gain seems to support this concept. "A single antibiotic can wipe out an entire intestinal microbiome," says Schwartz. "If antibiotics are infrequent, then the microbiome can recover. But if there are excessive antibiotics, then the impacts on the microbiome can last, and the ecology of the bacteria in the intestinal tract changes and doesn't go back to what it was before."
The team was able to account for other factors that may influence children's weight - however, they were not able to discount the influence of the mother's microbiome, which could have some effect on how the child's own microbiome develops. Some studies have suggested that babies who are not exposed to their mother's vaginal microbes via natural childbirth (born via Cesarean section) are more likely to be heavier and prone to immune conditions like asthma and allergies.
Schwartz warns that these results stress the need for antibiotics to be used sparingly and only when absolutely necessary. Frequent use could put children at risk of obesity, even if they are active and have healthy diets.
The study was published in the International Journal of Obesity.
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