Yogurt containing probiotic bacteria may protect children and pregnant women against the harmful effects of heavy metal exposure, according to new research from the Canadian Center for Human Microbiome and Probiotics. The findings are published online ahead of print in the journal mBio.
Heavy metals – which include arsenic, lead, copper, cadmium and mercury – have long been known to cause serious adverse health effects in humans. Pregnant women are advised to limit their intake of foods with high concentrations of heavy metals, which can cross the placental barrier and directly deposit in growing fetal tissue.
Other common pathways of exposure to heavy metals are breastfeeding, ingestion of contaminated food or water, inhalation of particulate matter, or ingestion as a result of hand-to-mouth behavior. Children and infants tend to have higher exposure to metals because they consume more food in relation to their body weight and absorb metals more readily than adults.
Past studies have identified a wide variety of harmful effects associated with heavy metal exposure, including but not limited to: low birthweight; stunted growth; kidney, lung, and intestinal damage; bone demineralization and resulting fractures; and a range of adverse neurodevelopmental effects (cognitive impairments; lower IQ; and attention deficit hyperactivity disorder).
The team behind the new research had previously studied the protective effects of microbes against environmental health damage in poor regions of the world. They found that one bacteria, Lactobacillus rhamnosus, was particularly adept at binding toxic heavy metals. Based on this finding, the team next wanted to know if regularly consuming this probiotic strain could be an effective way to prevent metals from being absorbed in the diet.
In addition, the team had been working with test kitchens in Mwanza, Tanzania, to produce a probiotic yogurt for the local communities. As Mwanza is built on the shores of a lake polluted with pesticides, mercury and other toxic metals, the team used this network to run a trial of a new type of yogurt containing L. rhamnosus.
The new investigation included 44 school-aged children, who were followed for a duration of 25 days, and 60 pregnant women, who were followed over their last two trimesters until birth. Upon intake, the researchers measured levels of toxic metals across all participants to obtain baseline data prior to “treatment” (yogurt consumption).
Probiotics demonstrate ‘significant protective effect’
In both groups (pregnant women and children), lead and mercury levels were found to be elevated by up to 6.8 times the average levels in developed nations, while levels of arsenic and cadmium were on par or slightly lower than averages across the developed world, the researchers report.
Participants were then randomized into treatment and control groups. Twenty-two children were randomly assigned to receive the L. rhamnosus yogurt, while the other 22 were allocated to the control treatment, which consisted of milk. Of the 60 pregnant women, 26 were randomly assigned to receive the L. rhamnosus yogurt and 34 were assigned to a control group that did not receive any intervention.
At follow-up, the researchers again measured participants’ blood levels of toxic metals. Unfortunately, a substantial number of participants dropped out of the study and/or failed to attend the follow-up, so the final analysis only included 36 children (18 in the treatment group; 18 in the control group) and 24 pregnant women (12 in the treatment group and 12 in the control group).
Still, a “significant protective effect” against mercury and arsenic was measured in the pregnant women, the team reports. Notably, blood levels of mercury and arsenic actually increased among pregnant women in the control groups but remained stable among women who received the L. rhamnosus yogurt, indicating that probiotic consumption may confer protection against toxic buildup of heavy metals.
“Reduction in these compounds in the mothers could presumably decrease negative developmental effects in their fetus and newborns,” says project leader Dr. Gregor Reid.
Future studies needed to confirm effects in children
Although the children in the study showed lower toxin levels after consuming the probiotic yogurt, the results were not statistically significant – possibly due to the small sample size and short duration of treatment, which might have limited the effect size in these groups. As the authors point out, the results comparing the short-term (children) and long-term (pregnant women) interventions suggest that probiotic consumption does not have a fast-acting effect, but rather acts over the longer term to reduce concentrations of heavy metals in the blood.
“This is likely because the mechanism of action involves prevention of uptake into the body from the GI tract, rather than scavenging what is already in the body, as occurs in chelation therapy,” the researchers explain. “Alternatively, it may be reflective of differing metabolic or hormonal differences and/or different indigenous microbes in the pregnant women compared to the [children].”
Further studies involving time course analysis – a blended research design and statistical analysis used to measure changes in one variable (levels of toxic metals) as a function of dosage and duration of another variable (probiotic yogurt consumption) – will help to resolve this discrepancy, the authors add.
“This work has demonstrated the potential value of long-term probiotic-based interventions to counter mercury and arsenic exposure in vulnerable populations, particularly in pregnant women,” the authors conclude. “This approach can be disseminated at an affordable cost (the equivalent of pennies) in developing countries where individuals are at high risk; however, it could also be applied to developed world citizens and wildlife, for example, those living near mining facilities.”
The team – who receives funding from the Bill and Melinda Gates Foundation – says they hope that these findings help provide a framework for further human trials. It is reasonable to presume health benefits due to reduced levels of toxic metals, the researchers say, but “long-term multiyear studies would help determine if reductions in toxin levels in the blood via consumption of probiotic foods result in improvements in physical and cognitive development in children.”
Other recent research into the protective benefits of probiotics
These latest findings add to a growing a body of research demonstrating the beneficial health effects of probiotics. In past studies, a variety of strains of probiotic bacteria have been identified as providing protective benefits against a wide range of adverse health conditions.
In July of this year, researchers at Vanderbilt University in Nashville, TN, genetically modified the bacteria Escherichia coli Nissle 1917 to craft an anti-obesity treatment that was found to be effective at lowering food intake in a mouse trial. In the same month, researchers from the Griffith Health Institute and School of Medicine at Griffith University in Australia published a study suggesting that blood pressure may be improved by consuming probiotics.
And in 2013, a study published in the journal Gastroenterology found that healthy women who consumed probiotics in yogurt experienced positive changes in brain activity. In that study, women consuming probiotics were shown to have enhanced connectivity between a brainstem region called the periaqueductal grey and the brain regions responsible for cognition. The researchers claimed their results demonstrate “that the gut-brain connection is a two-way street.”