Monday, 30 November 2015

A Mum's Guide To Dodgy Science: From Petri Dishes To People


Time for the second instalment of my "how to spot a dodgy science/health story" series. This one is more well known than Publication By Press Release and is one of the first questions to ask of any article claiming a new discovery kills, cures or otherwise alters your health:

Was this study done on humans like me?

All too often the answer to that question is no. The most notorious examples are probably the "Miracle Drug/Food Cures Cancer" headlines, where it turns out that the cancer being destroyed isn't in a person, it's just a bunch of cells in a dish. Certainly killing the contents of a petri dish may be an important first step in discovering a new treatment but the vast majority of stuff that can do that never makes it much further. Lots of things can kill cancer cells in a dish, domestic bleach works well, but I wouldn't recommend it as a medication.


Cartoon from the wonderful xkcd

But even if your new wonder drug does turn out to be safe, that doesn't mean it'll work in people. Firstly there is the issue of quantity. Cells can be given huge doses but humans might need to consume impossible amounts for it to do anything. Plus human beings are wonderfully, confusingly, unpredictably complex. Far more so than a single type of cell in a carefully controlled plastic environment. There are an almost infinite number of reasons why something that works "ex-vivo" (in the dish) will be a total flop in a full blown person.

It's not just cells in dishes that are the problem though. Moving on to whole animals isn't a guarantee things will work in humans. Fruit flies, Zebra fish and nematode worms are all popular "model organisms" but quite clearly very different to us. Even calling in our mammal cousins can't tell us everything.




I was reminded of this today when I read this particularly groan worthy story which claims that being born by Cesarean section could affect brain development. It draws this conclusion from a study done in mice and says that those mice born by C section showed increased brain cell death after birth and this may be linked to these mice having a different microbiome to those who got a good dose of mum's bugs on the way out.


(I'm not quite sure which is the most glaring error in this story, although the fact that the abstract it's based on says exactly the opposite, that cell death decreased not increased in the CS group, is probably a good place to start. I was seriously tempted to just write a whole blog pulling this story apart but I'm going to try to restrain myself and get back to the point....)

Fairly obviously mice aren't people. Laboratory mice definitely aren't the equivalent of a diverse human population. Neither the article or the abstract tell us what type of mice were used in this study but they were most likely one of many specifically bred laboratory strains with carefully selected and controlled characteristics. So something that is true in one strain of mice might not even be true of all of them.

This becomes even more important when the story starts speculating about the involvement of the microbiome (the bacteria that live in and on an individual). Different strains of mice have different microbiomes. Even identical strains raised in different labs will vary thanks to diet, environment and how strictly they are isolated from other germs etc. The microbiome is a fascinating field for study and will probably open up a whole new world of information about our bodies, but at the moment it is very much in it's infancy. We can't even accurately identify all the bacteria that are there, never mind how they interact. So it's a whopping great Olympic triple jump of a leap to suggest that something seen in baby lab mice, which may or may not be linked to their microbiomes, can tell us anything about the affect of differing microbiomes in humans.





Oh and it gets worse. Even humans aren't always a good model for other humans. Especially if the humans that need medical treatment are female. Historically, far fewer women have been included in clinical trials. There are lots of diseases that affect men and women differently so treatments tested mostly on males don't always work as well or in the same way in females. Our bodies also change more and more often. Hormone levels change throughout life and even over the course of a month. If you're pregnant, forget it! Since the horrors of Thalidamide almost nothing gets tested on pregnant women, (although there are some calls to change this).

Then there are the confounding variables of culture, diet, geography etc. etc. These could be subtle, biological interactions or something more obvious: Say a study claims that eating Kale makes you healthier because people who eat loads of it have less heart disease - does that mean there is something miraculous in the green stuff or could it just be that, in the experiment, the people who ate lots of Kale all lived in communities where everyone had a great diet and was very physically active?


Salad, the bringer of joy and laughter (in stock photo land)


None of this is to say that we should throw up our hands and ignore all scientific advice. But if you're going to make an alteration to your life based on it, then it's worth checking how likely it is to apply to you as an individual. Cells in a petri dish or mice in a lab are interesting, and certainly useful in early research and safety testing, but they aren't as complex as you. other humans are more comparable but if they are a different sex and/or living a totally different lifestyle you might want to think about what else could be going on.

Finally (I'm beginning to think I'll be ending every one of these posts like this), just don't put too much faith in health advice from newspapers, facebook shares and, of course, random people's blogs.

SBx

Ok I couldn't leave it alone, here's some other stuff I got annoyed with in that story about C section mice:
1- It's just a meeting abstract, nothing has been peer reviewed yet (see post on Publication By Press Release!) 
2- Even if there is an increase / decrease in brain cell death - how do we know the C section mice are worse off? This doesn't seem to have been tested, it's assumed natural is better but it's theoretically possible that the opposite is true.
3-It's one single (unpublished) study, many if not most individual papers turn out to be flawed so it should be taken with a big 'ole pile of salt until it's repeated by others.
4- The whole microbiome bit just seems to have been chucked in because it's a bit of a buzzword at the moment, especially with anything related to C sections. I'm amazed they didn't get epigenetics in there too.
5- The article speculates that brain differences may also be caused by C section babies not getting the "rush of hormones" during normal labour. Which may be true of lab mice having planned C sections but a large number of human c sections happen well after labour began *coughs* sometimes 34 hours after *coughs*
6- Wonderfully, for an article so full of extrapolation, speculation and a few baffling errors, it ends with the phrase: "having the full facts available before a choice is made is important."

Well yes it is.

*face palm*








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