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GidMK's profile
Health Nerd
Health Nerd
Health Nerd
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@GidMK

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Health NerdVerified account

@GidMK

Epidemiologist. Writer (Guardian, Observer etc). "Well known research trouble-maker". PhDing at @UoW Host of @senscipod Email gidmk.healthnerd@gmail.com he/him

Sydney, New South Wales
theguardian.com/profile/gideon…
Joined November 2015

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    Health Nerd‏Verified account @GidMK 12 Nov 2019

    In the last few weeks, there have been a bunch of headlines about how WATER can IMPROVE CHILDREN'S COGNITIVE ABILITY Thing is, the science doesn't appear to support that statement Let's look at the murky waters of dehydration and multitasking 🧵pic.twitter.com/oTYVLhDTrH

    6:32 PM - 12 Nov 2019
    • 16 Retweets
    • 21 Likes
    • Brent Hayward Rowena Alberga Christina Maie Lynn Bee, PhD Dr. Erin Williams Jasam Nitko Stephen Want Dr. Clare Conry-Murray Caitríona Lee
    1 reply 16 retweets 21 likes
      1. New conversation
      2. Health Nerd‏Verified account @GidMK 12 Nov 2019

        The study is here: https://academic.oup.com/jn/advance-article-abstract/doi/10.1093/jn/nxz206/5558303 … Fun fact - two of the authors work for Danone, who also funded the study and provided the water used Danone, incidentally, makes the popular brand of bottled water, Evianpic.twitter.com/TkLLrxxT9j

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      3. Health Nerd‏Verified account @GidMK 12 Nov 2019

        This was an interventional crossover trial What this means is that the participants (children aged 9-11yo) were all given 3 interventions one after anotherpic.twitter.com/A4KVvSODok

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      4. Health Nerd‏Verified account @GidMK 12 Nov 2019

        The interventions were: Low - 0.5L of water a day Ad Libitum (AL) - drink water as usual High - 2.5L of water a day For 4 days Remember, this is for children aged 9-11 (2.5L is A LOT of water!)

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      5. Health Nerd‏Verified account @GidMK 12 Nov 2019

        The researchers then tested the children at the end of the 4-day drinking period, looking at their urine to see how dehydrated they were, and doing 3 different cognitive tests

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      6. Health Nerd‏Verified account @GidMK 12 Nov 2019

        Now, this is where we run into our first hurdle The scientists report using a crossover design, but we don't know which period was first (Low, AL, High) What we DO know is that this trial doesn't report any randomizationpic.twitter.com/P1BUz9zWLU

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      7. Health Nerd‏Verified account @GidMK 12 Nov 2019

        This is an issue because people get better at cognitive tests over time That means it's possible that any results of the experiment are simply differences in timing of the tests (i.e. given at the beginning or end of the total trial)

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      8. Health Nerd‏Verified account @GidMK 12 Nov 2019

        Now, the researchers used a counterbalanced design, which is a method of trying to account for this issue The problem here is that the study doesn't seem to have been randomized, which means that it's likely that bias crept into the results!pic.twitter.com/mXcw1pEngE

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      9. Health Nerd‏Verified account @GidMK 12 Nov 2019

        That brings us to the next area of concern They excluded a quite a few participantspic.twitter.com/ILzsvHkjE5

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      10. Health Nerd‏Verified account @GidMK 12 Nov 2019

        In total, out of the 91 children who started the trial, 8 dropped out That's actually pretty good, only 9%!

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      11. Health Nerd‏Verified account @GidMK 12 Nov 2019

        But then, a further 7 were excluded because of 'poor hydration compliance' What does this mean? Essentially, the researchers thought they were drinking more/less water than their experimental conditionpic.twitter.com/PJXeqv0IG5

        1 reply 0 retweets 1 like
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      12. Health Nerd‏Verified account @GidMK 12 Nov 2019

        Now, this makes the study what's known as a per-protocol analysis Without going into the details, per-protocol analyses are KNOWN for giving spurious/misleading resultspic.twitter.com/o2G7Yissgq

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      13. Health Nerd‏Verified account @GidMK 12 Nov 2019

        But there's more - after excluding participants entirely, the study excluded between 5 and 21 children from each analysis in the study That's up to 28% of the remaining sample (!)pic.twitter.com/j0KfldJaV2

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      14. Health Nerd‏Verified account @GidMK 12 Nov 2019

        This was due to "poor cognitive data" What does that mean? Well, according to the study, it means that these kids had results that were considered 'outliers' or 'poor performance'pic.twitter.com/70Z3ZHH8rl

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      15. Health Nerd‏Verified account @GidMK 12 Nov 2019

        Astute readers will note that this means that apparently 8/64 (13%!) of the children had results more than 3 standard deviations from the mean in the go/no-go task That seems...unlikely

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      16. Health Nerd‏Verified account @GidMK 12 Nov 2019

        To give you an idea of how unlikely, I ran the mean/standard deviations through SPRITE (thanks @sTeamTraen @jamesheathers) for 100 repetitions, and didn't get a single distribution with more than 3% of results >3 SDs from the mean So...maybe possible? VERY weird

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      17. Health Nerd‏Verified account @GidMK 12 Nov 2019

        (Check out SPRITE here https://peerj.com/preprints/26968v1/ …)

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      18. Health Nerd‏Verified account @GidMK 12 Nov 2019

        Also, if you look at the children that they excluded for "poor hydration compliance", they talk about an "a priori" defined criteria for exclusion This is something that you'd usually declare in your pre-registration. Let's check their's outpic.twitter.com/fcNm4YsOfG

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      19. Health Nerd‏Verified account @GidMK 12 Nov 2019

        The pre-registration is...not great Firstly, no a priori exclusion criteria for urinary values. That's a problem, because it means that we have no way of knowing if the study authors decided to exclude these 7 children before the study or after looking at the results 😕pic.twitter.com/ipMm6CPCPJ

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      20. Health Nerd‏Verified account @GidMK 12 Nov 2019

        But there's more! The pre-registration completely contradicts the study protocol in numerous ways😮 The number of participants, age brackets, intervention arm protocol, inclusion/exclusion criteria, testing schedule, and outcome measures are different! That's worrying

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      21. Health Nerd‏Verified account @GidMK 12 Nov 2019

        It almost sounds like a completely different trial, but the authors and name/number are the same You can compare the pre-reg to the study here:https://clinicaltrials.gov/ct2/show/record/NCT02816450?term=NCT02816450&draw=2&rank=1 …

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      22. Health Nerd‏Verified account @GidMK 12 Nov 2019

        So, after all of this, what did the study find? Hilariously, there was NO EFFECT of water intake (AL/Low/High) on any cognitive test!!!!pic.twitter.com/kC75Y16GdT

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      23. Health Nerd‏Verified account @GidMK 12 Nov 2019

        In other words, the PRIMARY FINDINGS of this research project is that drinking more/less water DOESN'T IMPACT CHILDREN'S PERFORMANCE ON COGNITIVE TASKS That's the exact opposite of what the media reportedpic.twitter.com/uaa7gSlEpu

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      24. Health Nerd‏Verified account @GidMK 12 Nov 2019

        What they DID find, and what was then converted into the headlines, was that if you look WITHIN GROUPS, there were some statistically significant trends, where better urine markers of hydration led to better accuracy on the testspic.twitter.com/8m5mwUGbVF

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      25. Health Nerd‏Verified account @GidMK 12 Nov 2019

        I.e. if you look just at kids when they were in the AL condition (drinking as much water as they wanted), those who had more concentrated urine appeared to be slightly less accurate on some cognitive tests

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      26. Health Nerd‏Verified account @GidMK 12 Nov 2019

        But remember - there was no difference between conditions In other words, perhaps dehydration affects cognition, but drinking more/less water doesn't appear to make any difference

        1 reply 1 retweet 4 likes
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      27. Health Nerd‏Verified account @GidMK 12 Nov 2019

        Here's the main table of results As you can see, there are really very few differences between the three groups on any test for reaction time or accuracypic.twitter.com/jdzJ4do8AH

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      28. Health Nerd‏Verified account @GidMK 12 Nov 2019

        Moreover, it's very hard to tell if the statistical tests were controlled for multiple comparisons, which is concerning because many of the p-values were between 0.03-0.05pic.twitter.com/kCMktXnc3t

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      29. Health Nerd‏Verified account @GidMK 12 Nov 2019

        And, reminder, this was an industry-funded trial, which makes the reporting of the apparently negative findings even more worrying

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      30. Health Nerd‏Verified account @GidMK 12 Nov 2019

        Also worth noting that the study didn't really look at multitasking per se, this was based on an extrapolation from the within-group tests that looked at cognitive load!

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      31. Health Nerd‏Verified account @GidMK 12 Nov 2019

        TO RECAP: - industry-funded trial - potential issues with study design - strange numbers - results NEGATIVE for primary outcome - didn't look at multitasking - somehow still reported as "water helps multitasking"

        1 reply 0 retweets 1 like
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      32. Show replies

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