Is our love affair with antibiotics slowly killing us?
Feel a chest infection coming on? Think twice about those antibiotics you've been prescribed, as overusing them could be eliminating your vital microbes, and causing diabetes, allergies and obesity, according to one expert. Our reporter delves into the science of the microbiome
Published 25/08/2015 | 02:30
Scientific breakthroughs in medicine and food production have given us a modern lifestyle which is healthier and easier than our ancestors could have dreamed of - but at what cost? Is it possible that our easy access to antibiotics and cheap meat is having a deeply negative effect on the health of both adults and children?
Dr. Martin Blaser, an MD who specialises in infectious diseases, believes it is. A renowned expert on infectious diseases and the beneficial role of bacteria in human life, Blaser believes that the overuse of antibiotics has fuelled many of the modern plagues in the western world, including obesity, diabetes, allergies and chronic inflammatory diseases.
Every human being, Blaser explains, is populated by microbes which live both on and in us in incredible numbers and diversity.
Everyone's population of bacteria or microbes - our individual microbiome - is extremely important, because different strains of bacteria perform different functions for us.
"Microbes are very useful to us," explains the director of the Human Microbiome Program, NYU Medical Centre in New York and author of the bestselling book Missing Microbes.
"They help us digest food, make vitamins and train our immune system to protect us against pathogens."
Our microbiome is ancient, he explains. Much of it is handed down through the generations, from mother to child, but Blaser believes that modern lifestyles are impacting on it - and fundamentally changing it.
"Our ancient microbes are disappearing because of everything from antibiotics and Caesarean sections to clean water and different kinds of anti-bacterial substances in our food.
"We don't know all the causes - or the significance of what we have lost - but there is more and more evidence that we have lost nearly half of the diversity in our microbiome."
And this, he believes, has serious consequences for our health.
Blaser believes that what he calls the "modern plagues" - conditions such as obesity, Type 2 diabetes, asthma, coeliac disease, autism and food allergies - have all flourished around the world in the decades since World War Two.
Since World War Two, he explains, the incidence of a collection of about 10 diseases has been rising dramatically. Why is it, Blaser asks, that these conditions all began to flourish about the same time?
"Either there are 10 different causes or there is one cause that is beneath them all. My hypothesis is that antibiotics are a big part of it."
Think about it he says - modern children get antibiotics from the first year of life and farmers have been using them in food production for decades.
"We may have been getting very low doses in food and water. What is perhaps most the alarming and sad part of this is that my theory is that this is cumulative across the generations."
In other words, he explains, because mothers pass on much of their microbiota to their infants, if one generation after another of mothers are losing diversity, then they are passing that reduced diversity to their offspring.
And those children are losing more.
Blaser believes that's because every time we take an antibiotic, some microbiota in our systems disappear - and modern children receive a lot of antibiotics.
"Everyone knows antibiotics are essential drugs - and they are. However, we all saw the benefit, but not the cost. The cost is that consuming antibiotics is having an effect on our microbiome.
"My theory is that every time you take an antibiotic a few organisms disappear - and that this is cumulative across the generations.
Infancy is a critical time. It's the period when babies develop their metabolism, their immunity, and their cognition. It's now also the time when their microbiome starts to disappear, he warns.
In the USA, Blaser observes, the average child gets three courses of antibiotics in the first two years of life. By the time that child is 10, he or she may well have received 10 courses of antibiotics.
By age 20 that may have risen to 17.
In other countries such as France and Italy, the number of courses a child will receive antibiotics is higher, he says, in countries like Sweden and the Netherlands, it's lower.
"I wrote my book to tell parents that antibiotics are wonderful drugs - but there is a time to use them and there is a time for them not to be used.
"We have all these thousands of species in our body. However some are very dominant, and others may just be few."
Historically, it was believed that if you took an antibiotic and you had billions of organisms of a particular species, they bounced back later on.
"That's what three generations of doctors were trained to believe," says Blaser.
"However, my thinking is that the antibiotic can completely wipe out a species that is low in number - and these do not bounce back."
It's not a scientific fact, he says, just a theory, but "the mathematics suggest it," as, he warns, does his comprehensive series of experiments on mice. And that's not the only battering meted out to the human microbiome by modern life.
"I have known for 30 years that farmers gave antibiotics to farm animals to fatten them up through growth promotion.
"The animals would gain weight faster and use feed more efficiently. They found that the earlier in life they started this, the more powerful the effects.
"I had known for a long time but all of a sudden I asked why the antibiotics were doing that - and I started asking what they were doing to our children."
Blaser began a series of studies, in which mice were given antibiotics - or not.
He and his researchers found that by using antibiotics, they could change the development of the rodents - how much fat or muscle they put on, how rapidly they developed bone and how their immune system matured.
Essentially, he says, what happened was that when mice were put on antibiotics they got fat.
Further experiments showed that the rodents also gained weight on a high fat diet.
"If we put them on both (antibiotics and a high-fat diet) they got very fat," he reports.
Next, they decided to see how long the impact of the antibiotics lasted.
"We gave the antibiotics for a very short time and then stopped."
The result? While the mice were receiving the antibiotics, their microbiome was disrupted.
However, when the course finished, the microbiome seemed to return to normal - but the mice still became fat. So it seems, concludes Blaser, that disrupting the microbiome at an early age has an effect on the metabolism.
It's well known that early life is important to a baby's development in many ways - in fact that when something happens to a baby early in life it can stunt its growth.
But when he and his research team disrupted the mice microbiomes, the results were accelerated growth.
"Immunity is very complex," he warns.
Essentially, Blaser believes that our microbiome is under attack from our modern westernised lifestyle. If we subject the microbiome to further impact on it in early life, he believes, the negative facts may be even more serious.
"My hope is to turn back the dial, so that in examining rooms around the world the doctor will say 'let's wait a few days' and the parent will say 'okay'."
Blaser's theories are borne out of research by Dr Maria Gloria Dominguez-Bello, a microbiologist, and associate professor at the Department of Medicine at New York University School of Medicine - and Blaser's wife.
Bello studied the microbiota of isolated tribes whose lives have not been impacted upon by modern medical advances, comparing them to people in more developed parts of the world.
Her findings are mind-blowing.
"We were the first to compare microbiomes across continents," she says.
"I worked with tribal people in South America and Africa - hunter/gatherers who are outside the western lifestyle. We compared the microbiomes of healthy people in the USA with those of rural people in Malawi and with rural Native American Indians in Venezuela.
"The highest diversity was in Venezuela. This was followed closely by Malawi, and then, very much below this, was the level of diversity in the US adult.
"We do seem to be losing bio-diversity."
There's more. Bello published research earlier this year on the microbial diversity of the Yanomami tribe on the borders of Venezuela and Brazil, a people who have had had no contact with Westernisation.
In 2009 the tribe was contacted by health teams: "Swabs collected and we were able to sequence and study the microbes in their oral cavities, skin and faeces.
"We found that they had a much higher diversity than even the rural populations we had encountered before. The difference between the Yanomami and the rural Venezuelan Indians, for example, was as high as the difference between the rural Venezuelans and the US adults."
In fact, says Bello, the Yanomami exhibited almost twice the microbial diversity than that in the healthy US population.
"The paper was published just this year, but it confirms our previous association that where we westernise, we lose diversity.
"We don't know what is the direct consequence of this, or what it is costing us, as regards our health, but there are strong associations in being westernised and improving our control of infectious disease - but at the same time we are seeing a horrendous increase in the immune and metabolic diseases.
"As we become more westernised, the risk of Type One diabetes which is an immune disease, for example or coeliac disease increases.
"These are diseases that indicate a malfunction of the immune system," says Bello.
"We think the lack of diversity is behind these diseases, or that the lack of key bacterial species is behind it. That would be species which educate the immune system when we are very young.
And there's something else.
Bello also researched the impact of Caesarean sections - another sophisticated modern medical procedure which has become an increasingly routine process in American maternity hospitals.
Bello found that babies born through C-section lacked a crucial maternal bacteriological legacy:
"When babies are born, their immune system needs to discriminate between the good guys and the bad guys - it must learn to tolerate the friends and to fight the pathogens.
"This training starts after birth with immediate exposure," says Bello.
However, she explains, an infant's first exposure to microbes takes place during the birth when they interact with the mother's vaginal microbes. That starts in labour."
The process of being born is far more than simply crossing the birth canal, she points out - labour usually takes several hours, so there's plenty of time for this interaction to take place.
"So mammals are born already inoculated with the maternal birth-canal microbiota.
"However, things that we do in the West that impacts on this includes the C-section. We are the only mammal that has babies without the normal maternal inoculum."
Research shows that C-section babies lack that maternal inoculum, she warns.
"Typically in the US babies have an average of three antibiotics courses by age two, and this is another impact. If they are born via a C-section and then have antibiotics, we believe that will have a compounded effect on their microbiome.
"We think these two effects may be behind the association between westernisation and loss of diversity."
* Dr Martin Blaser and Dr Maria Julia Dominguez-Bello will speak at the launch of the APC Microbiome Institute at UCC, Cork on Friday August 28.
* Dr Blaser will give the inaugural Annual APC Distinguished Lectureship 'How early life microbes shape human development' at the APC Microbiome Institute Launch Symposium.
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