|Dr. Martin J. Blaser thinks Americans could use fewer antibiotics. “My guess is that we can markedly reduce antibiotic use in this country without undue harm to human health,” he said.
Over-prescribing antibiotics might upset the balance of microorganisms in the digestive tract and lead to serious health problems. So believes Dr. Martin J. Blaser, who gave a Contemporary Clinical Medicine: Great Teachers Grand Rounds Lecture in Lipsett Amphitheater on Feb. 12.
Every person is home to trillions of bacteria and other single-celled organisms, said Blaser, director of the Human Microbiome Program at New York University’s Langone Medical Center. There are at least 10 times as many microbes as there are human cells. These microbes contain a combined total of 2 million unique genes—perhaps more.
Exposure to microbes begins during birth, Blaser explained. These microbes, mostly bacteria, colonize every part of the body—the skin, the mouth and the digestive tract. Microbes continue to diversify until babies are about 3 years of age.
“These first 3 years of life are when the microbiota is most dynamic in humans,” said Blaser. “It’s also the time when babies are developing their metabolism, immunity and cognition.”
Microbes have coevolved with humans over thousands of years, he said. Take, for example, Helicobacter pylori, a spiral-shaped bacteria found in the mucus lining the stomach. Since 1982, H. pylori has been associated with peptic ulcer disease.
In fact, scientists believe that H. pylori has colonized humans for at least 100,000 years. Until recently, Blaser said, H. pylori colonized just about every human stomach. Today, the bacteria is found in only 6 percent of children. Blaser believes antibiotic use may explain part of the disappearance of this bacteria from human stomachs.
“We know that there have been changes in physiology from the H. pylori-colonized stomach to the H. pylori-free stomach,” said Blaser. He noted that in the absence of H. pylori, the incidence of peptic ulcer disease decreased. He also noted there has been an increase in acid reflux.
Blaser also believes that antibiotic use may help to account for the dramatic rise in the obesity rate in the United States since 1990.
Back then, 12 percent of the population was overweight. Today, almost a third of the population is overweight. He noted that, if children are overweight by age 5, they tend to stay overweight for the rest of their lives.
In the 1940s, he said, farmers discovered that livestock gained weight faster when fed low doses of antibiotics. The youngest livestock grew fastest when given antibiotics. Blaser suspects this increased weight gain may be due to more than eliminating the damage of disease-causing organisms.
“This suggested to me that we’re looking at a developmental phenomenon,” said Blaser.
To investigate his hunch, Blaser’s students fed mice antibiotics for their entire lives. In one study, they observed that a continuous diet of low-dose antibiotics changed the mice’s fat composition. In another, his team found that mice that were fed a high-fat diet and low-dose antibiotics gained even more weight than mice fed a high-fat diet and not given antibiotics.
Children, however, don’t receive low-dose antibiotics. According to Blaser, they receive high-dose antibiotics to treat ear infections, for example. A student in Blaser’s lab fed young mice high-dose antibiotics at three different intervals early in their development to mimic doses that children receive. The student found that three doses early in life were sufficient to increase the mice’s fat tissue well beyond the last dose of antibiotics.
Blaser thinks Americans could use fewer antibiotics. In Sweden, antibiotic use is lower than in the U.S, yet there are no epidemics. “My guess is that we can markedly reduce antibiotic use in this country without undue harm to human health,” he said.