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The full extent of people's health problems that might be helped by taking probiotics has not yet been realized, experts say.
"The future is bright for probiotics, but we need to get a lot more work done," said Dr. Allan Walker, a professor of pediatrics at Harvard Medical School and an investigator at the Mucosal Immunology and Biology Research Center at MassGeneral Hospital for Children in Boston.
For example, researchers would like to better understand how probiotics work in the body, and pin down the exact organisms and amounts of them responsible for their beneficial effects along with studying the conditions where probiotics may be most helpful.
When he looks at what lies ahead for probiotics, Walker said he can envision people taking probiotics before heading to developing countries, to help prevent traveler's diarrhea from contaminated food or water. He also imagines that some day, babies born into families where allergies are common will be given specific probiotics during infancy to protect them from developing allergies. However, the evidence to strongly recommend probiotics for either of these purposes is not yet there, he said.
It might seem surprising that the microbes lining the intestinal tract can have far-reaching benefits beyond the digestive system. But bacteria in the intestines are very important to health and are almost like another organ system, Walker said.
Gut bacteria provide substances involved in supporting immune activity, thwarting bad bacteria and preventing inflammation that can have profound effects on other parts of the body, he said. [8 Tips to Be a Probiotic Pro]
Research has also shown that the influence of gut bacteria begins at an early age. Any disruption to the initial colonization process of intestinal bacteria in infants during their first year of life is thought to be the basis for disease later in life," Walker said.
As researchers explore the influence of gut bacteria on health and disease, here are three areas where probiotics may prove helpful, but further study is needed.
There's promising evidence that obesity can, in part, be caused by a change in bacteria in the intestine, Walker said. Early studies in mice as well as preliminary findings in people have shown that obesity is linked with a less diverse community of intestinal bacteria compared with people who do not have weight problems.
An exciting area of obesity research is exploring whether giving someone who is overweight beneficial bacteria might change the composition of their gut bacteria in a positive way, to alter their metabolism and inflammatory responses. Increasing the number and types of good bacteria may potentially help people to absorb fewer calories from food, lose weight and reduce body fat — but science is just beginning to explore these connections, so it's too soon to recommend probiotics as a way to shed pounds.
Further research might also help to determine the underlying mechanism that explains how probiotics influence metabolism and affect body weight, as well as identify the most effective strains and dosages of them.
Researchers have found a link between low levels of intestinal bacterial diversity in infants during the first months of life and a greater risk of developing allergies and eczema. As a result, scientists are investigating whether probiotics could play a role in preventing allergies in children.
Many studies, especially in Finland, have focused on eczema, a common allergic condition in babies and young children that produces an itchy red rash on the face and other parts of the body. They are experimenting with giving beneficial bacteria to pregnant women during the last two to four weeks before giving birth, as well as to breast-feeding mothers and to babies in families with a high risk of allergies.
Early evidence has shown that giving good bacteria to mothers and to babies increases the microbial diversity of the gut early in life, and it appears to help the child's immune system to fend off developing allergies. But more research is needed to know how long this allergic protection might last, and which bacterial strains offer the most benefits.
Some children with autism spectrum disorders suffer from gastrointestinal (GI) symptoms, such as diarrhea, constipation, vomiting and stomach pain, and these children often also have more behavioral difficulties, including irritability, anxiety and social withdrawal, compared with autistic children without GI complaints. It's not clear why these GI symptoms occur in children with autism, or how many children they affect.
Preliminary research in mice with autism-like symptoms and also in children with autism is looking into whether probiotics might offer any benefits for improving behavior as well as relieving GI symptoms in children with autism.
Another promising line of research is investigating the composition of intestinal microbes in children with autism compared with their healthy siblings and other healthy children who don't have the disorder. Studies at Massachusetts General Hospital in Boston have found early evidence that some children with autism have imbalances of gut bacteria, but researchers still need to determine which bacteria are involved and what role they might play in autism.
A new area of investigation is whether the nature of intestinal microbes in the mothers of children who develop autism may also be a risk factor for the disorder, Walker said.