Science News

Kids need to eat dirt to be immune

Thu, 7th Feb 2013

Chris Smith

A dose of dirt might be what the doctor ordered for a healthy immune system, new research has shown.

Stanford immunologist Mark Davis, who led the study which is published this Human lymphocyteweek in the journal Immunity, compared the spectrum of immune cells contained in blood samples from adult donors and new-born babies.

Focusing on a subset of white cells called CD4 lymphocytes, which orchestrate the immune response by recognising pathogens and stimulating other cells to attack, Davis and his team found that, in the adults, there were CD4 cells capable of recognising all of the pathogens they tested.

Furthermore, up to 90% of the CD4 cells were memory cells; that is, quick-reacting cells that are made when an individual has met a particular threat previously.

The samples from the babies showed that they too had cells capable of recognising the pathogens, but, as one might expect, none of these cells were memory cells.

On it's own, this result doesn't sound surprising, until one realises that the adult donors had not actually ever been infected with some of the pathogens - such as HIV - being tested by the team.

So where were these memory cells coming from in the adults? "We don't know for sure," says Davis.

But he speculates that infections with low-virulence bugs trigger the immune system to develop also responses to other related bugs it hasn't seen before.

"We think this happens by about age ten," he says. "Now we need to work out how to prove it," because obtaining blood samples in this age group is tricky.

Davis likens the development of the immune system to the maturation of the brain.

"The brain needs to have input from the eyes for the visual system in order to see properly. The immune system's no different. It needs stimulating in childhood to make it develop properly."

Moreover, the findings might also explain why young children are much more vulnerable to infections that adults tend to brush aside. The difference, of course, being that, in adults, these immune memory responses discovered by Davis will have matured, so the adult immune response is far more robust and effective.

"Kids need to eat dirt!" says Davis, stirring his morning coffee, hopefully with a dirty spoon...

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I personally believe we have got the whole bacterial thing scarily wrong and I hope its becoming obvious to the point of stopping the obsession with killing them all and being anti bacterial.
A recent article in New Scientist showed that the bacteria that live on fruit flies as a result of their diet actually determines the sex partners they choose.  So fruit flies eating one type of food will not mate with fruit flies eating another type of food because their biomes are distinctive.
It has been shown that hospitals that open their windows reduce the rate of bacterial infections and bacteriotherapy can rid people of chronic digestive disorders.  We need our bacteria and I think manufacturers of soap products have a moral obligation to stop selling anti bacterial anything except toilet cleaning products maybe.
In one of James Herriots fantastic books he told the story of the kids that lived in the abattoir and played in the piles of entrails out the back and also being the healthiest kids in the county.  We need our bacteria! Minerva, Sun, 10th Feb 2013

I've always had a problem with this idea, because I feel as though it encourages poor hygiene. Let's not beat about the bush here, the development of hygienic practices and sanitation over the past 100-200 years has been one of the top medical advancements of all time. The issue is that people take things into extremes -- living in an operating theatre is not great for your health, but neither is encouraging people to eat copious amounts of dirt in the name of immunity. Everything must be taken in moderation. Kids should be allowed to play outside and get dirty, but equally they should be made to wash their hands before meals and after going to the bathroom



schneebfloob, Sun, 10th Feb 2013

I think you are right but only because people don't understand the difference between good and bad hygiene - mostly through scaremongering tactics of cleaning product advertisements.  Its correct to say your baby's highchair table will have more bacteria than a toilet bowl but what they fail to say is it is totally different bacteria to those found in a toilet bowl and it is incorrect to state that ALL bacteria are bad for the sake of a few prevalent nasties (whose success is down to our own meddling in bacterial matters that we don't understand).

Of course you wash your hands before a meal, that principle of good hygiene has been understood since old testament times.  But sterilising every surface of your kitchen/house? That is bad hygiene.  Washing your vegetables is good hygiene, sterilising them is bad hygiene.  Your immune system develops as a result of your environment so children that have grown up in a slaughterhouse will be able to play in entrails.  Children who have grown up not exposed to entrails would be probably get sick if they played in them and that's why its important to be exposed to bacteria-so that your immune system is prepared for many eventualities.

In your own house it is sensible to take elementary precautions towards hygiene but detrimental to be overly generous with the bleach.  It is only in places where many different people congregate that more extreme precautions need apply such as in restaurant kitchens and hospitals but even then it is shown that many outbreaks are caused because people simply didn't wash their hands rather than because they didn't use enough bleach. Minerva, Sun, 10th Feb 2013

I've always believed that if a pacifier wasn't intended to get dirty, then kids would not drop them on the floor all the time!!!  And, if kids weren't meant to put everything they can get their hands on into their mouths, they wouldn't do it.

While washing hands with plain soap and routine cleaning may be good, there is no place in the home for a bunch of antibacterial products.  Leave those for the hospitals where they are needed.

There is a significant amount of evidence that some conditions such as asthma have a lower prevalence in rural children than in urban children, which would indicate a protective effect of exposure to certain types of dirt, dust, livestock, and etc.

Keep in mind that one of the first vaccines (of sorts) discovered was cowpox.

Also, keep in mind that there are different types of "germs", and they shouldn't all be treated the same.  There is "normal flora" found on the skin, and throughout the GI system.  And, of course, a lot of not very pathogenic environmental microbes, at least if they don't get under the skin.

An infant will get a dose of maternal antibodies at birth and from the milk.  However, these will eventually disappear, and the child will have to make its own antibodies to the environmental microbes, flora, as well as pathogens. CliffordK, Sun, 10th Feb 2013



The difference is that being overly lax on hygienic practices is far more dangerous than overly cleaning your house. I really do not think that parents should feel the need to go to 'special lengths' to encourage the development of their child's immune system. The immune system will develop as they mingle with other children at school, walk to school and play outside. It's inevitable.

This message is one I that very much worry will get lost if care is not taken. People have to understand that hygiene is not a bad thing. Those arguing that parents should not overly sterilise their homes must also spread the message that this is not an excuse to toss hygiene in the bin. That is what frightens me. schneebfloob, Sun, 10th Feb 2013

Well-you cant worry about how every individual interprets the information they take in. Some will get it some wont-thats humans for you....  :) 

And I also think you are wrong that being overly sterile in the home isnt harmful-I think it is harmful.  Not having the correct balance of gut flora leads to all kinds of metabolic and auto immune disorders and also has serious effects on mental health.  If peoples diets were optimal I would agree with you that being overly sterile in the home is not a problem but because gut flora is already badly unbalanced by a bad diet simple hygiene is better-wash your hands before you eat is enough.

I dont want you to misunderstand me - I'm not advocating that people should go roll their children in entrails - far from it.  But I do think that sterilising every surface in the house all the time is very detrimental to health. Minerva, Mon, 11th Feb 2013



On the contrary, we must worry about what people will take away from this message. It is our responsibility because it is the scientific community that is sending the message. If you tell people that over cleaning is damaging, people will stop cleaning their homes. Sure, these people may rear children with a more developed immune system (which is all that the link is suggesting) but they will also be more likely to succumb to conditions associated with bad hygiene. I think it's fairly apparent that the problems associated with poor hygiene are far worse than those associated with overly zealous cleaning. So, I really have to question the point of blaring out to people that they shouldn't over-clean their surfaces when it's likely going to be more problematic than what's going on at the moment.

I'd also like to see the evidence for your claim associating over-cleaning with mental health problems and metabolic disorders. Has this been conclusively shown? schneebfloob, Mon, 11th Feb 2013


Yes, we already have a significant number of "anti-vaccine" parents, and previously "conquered" diseases are on the rise. Lmnre, Tue, 12th Feb 2013

I don't get too worried about germs within my own house.

There are very few pathogens that I haven't been exposed to that can enter my house from an exogenous source, and then get amplified to the point where they would cause a risk of a serious infection.

Hmmm
Botulism Toxin
Staph Aureus Toxin
Other food being brought in? 
Perhaps some yeasts and molds.

That doesn't mean that a public place, a shared restroom or a cafeteria isn't without risk. CliffordK, Tue, 12th Feb 2013



On the contrary, we must worry about what people will take away from this message. It is our responsibility because it is the scientific community that is sending the message. If you tell people that over cleaning is damaging, people will stop cleaning their homes. Sure, these people may rear children with a more developed immune system (which is all that the link is suggesting) but they will also be more likely to succumb to conditions associated with bad hygiene. I think it's fairly apparent that the problems associated with poor hygiene are far worse than those associated with overly zealous cleaning. So, I really have to question the point of blaring out to people that they shouldn't over-clean their surfaces when it's likely going to be more problematic than what's going on at the moment.

I'd also like to see the evidence for your claim associating over-cleaning with mental health problems and metabolic disorders. Has this been conclusively shown?


I would like to see evidence for that claim too but since I didn't make it I cant provide it.  I have highlighted in red what I said and that is that an unbalanced gut flora can cause metabolic diseases and mental health issues.  I will provide you with the links later when I have finished work.

The message needs to be correct but the message will be whatever the popular press and media make of it-as has always been the case with research. The human body is immensely adaptable as long as you do it gradually-there is an American guy living solely on rotting meat (Aajonus Vonderplanitz).  A plate of that would probably kill you or me but if you had a fancy for it you could train your body to accept it. 

One of the biggest spread of diseases is from not washing hands and from my observations of people in this country its not something we practice well.  I had the misfortune of sharing a wall with the toilets in my old office and we could tell from the timings from flush to door opening that very few people stopped to wash their hands (plus we could hear the tap running...or not as the case may be).  You are more at risk from the germs on public transport than you are from an unbleached kitchen surface (and don't go on the London underground......). 

I think you also underestimate the intelligence of the public at large-you talk as if everyone will stop showering and just wallow in their own filth on the strength of the news that bacteria actually perform important functions in this world and I don't think that's the case. Minerva, Thu, 14th Feb 2013

No, you may not have explicitly stated it but you did imply it.



You have stated, explicitly, that you think over-cleaning is harmful. You have then proceeded to mention that gut flora imbalances apparently cause certain issues. You have then suggested that 'over-sterilization' in conjunction with gut flora imbalances is a problem. I would like evidence showing that over-cleaning in ones home exacerbates problems caused by gut flora imbalances, or, as you explicitly stated, that 'simple-hygiene' is better under these circumstances.

Moreover, if I have taken something from your message that you did not intend (I apologise if I have) then it simply demonstrates the care that needs to be taken when talking about this. Hand-washing is, as you have said, very important. But, you have also said over-cleaning is a problem. Would excessive hand-washing be considered a problem? People might ignore washing their hands once in a while, because they've been told that 'over sterilization' could be bad for their health.

I may indeed underestimate the intelligence of the public at large. But, in circumstances relating to health it is far better to assume the worst than to assume the best. You must assume that the public will take a message to extreme levels, because then at least you're prepared for it. schneebfloob, Thu, 14th Feb 2013

I haven't got much time but here are some links-I'm not sure if the last one will work but if you go onto the New Scientist website and enter bacteria cause speciation it will come up with about 10 relevant articles.

http://www.motherjones.com/tom-philpott/2013/02/meat-industry-still-gorging-antibiotics

http://www.newscientist.com/article/mg15821387.200-wet-hands-given-a-towelling.html

http://www.newscientist.com/article/dn9357-the-dirty-truth-about-allergies.html

http://www.newscientist.com/article/mg21729044.100-bacteria-boost-fixes-symptoms-of-autism-in-mice.html

http://www.todayszaman.com/news-285114-sterile-environments-can-be-unhealthy.html

http://www.newscientist.com/search?doSearch=true&query=bacteria+cause+speciation


In an age where some farmers have become resistant to all antibiotics through feeding them to their livestock and a couple of generations of people have been overdosed on antibiotics people need to be exposed to bacteria not protected from them.  Bacteria have been at the survival game a bit longer than humans - I think we didn't take care in our dealings with them and its coming back to bite us in the backside big style. Minerva, Thu, 14th Feb 2013

But could our cleanliness be the root cause of athsma and hay fever?

Cowpox certainly proved to be our great allie in the fight against smallpox.

But I think being overly clean could lead us down the path to our defense systems becoming vestigial. I think a little exposure to bacteria is a good thing. Of course that does rather depend on the bacteria we expose ourselves to and allowing our defense system to combat the intruder, rather than turning to antibiotics at the drop of a hat. Don_1, Tue, 19th Feb 2013

Look at how we immunise for viruses, a little of the thing that kills you, the body recognises and fights back with the cavalry immune system. It is easy to imagine the same scenario with bacteria, a little picked up here and there and body is strong to fight it for when a case of massive amounts are accidentally ingested. So for me, this highly suggests over-cleaning would weaken a persons resistance compared to a normal cleaning standard. With this sort of thinking , any bugs our immune system will fight  may just increase the strength of the immune system that can carry over to fighting with new bugs etc.  In my imagination there is wars going on  and it seems bacteria can be made our ally - perhaps only as sparring partners for the immune system. Fight on little buddies! majorminor, Sun, 7th Apr 2013

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