Does Shower Temperature Affect Brain Speed?

In November I learned about benefits of cold showers. So I tried them. I took cold showers that lasted about 5 minutes. I liked the most obvious effect (less sensitivity to cold).

Maybe a bigger “dose” would produce a bigger effect. Maybe the mood improvement cold showers were said to cause would be clearer. So I increased the “dose” in two ways: (a) more water flow (I stopped holes in the shower head) and (b) lower water temperature. After a week or so with the stronger dose, I saw I was gaining weight. It could be the cold showers, I thought. Fat acts as insulation and I couldn’t think of another plausible explanation. So I went from cold showers back to warm showers (48 degrees C.) — this time with greater water flow. My warm showers were 5-10 minutes long.

I began to lose weight, suggesting that the cold water did cause weight gain. More surprising was that my arithmetic speed (time to do simple arithmetic, such as 7-3, 8*4) began to decrease. Here is a graph of the results.

2011-01-04 shower temperature and arithmetic speed

Before the cold showers started my arithmetic speed was roughly constant. The mild cold showers had no clear effect. I had noticed the increase during the strong cold shower phase but hadn’t paid it much attention — I suppose because it seemed implausible. These results, however, are excellent evidence for cause and effect: cold showers made me slower, warm showers made me faster. The arithmetic tests weren’t done soon after the shower. There seems to be some sort of brain-speed adjustment that takes place over ten days or more.

I’ve never heard of anything like this, whereas I’ve heard many times is that cold showers are good. There is one complication, which is that December 3rd I stopped eating walnuts. I believe walnuts are bad for the brain, in contrast to the usual belief. I came to believe that because of results from two students of mine who had tried eating them. Improvement due to no longer eating walnuts would explain why line fitted to the strong cold data starts below where the weak cold line ends.  The final days of the strong warm phase may be the same as the weak warm phase when adjusted for the walnut difference.

What explains this? Maybe the weight change. When gaining weight, maybe fat was taken from the blood to be deposited in fat cells, thus lowering the fat content of the blood reaching the brain and thus degrading brain performance. Losing weight, the opposite happens. Eventually the weight loss will stop; this explanation predicts when that happens the warm-water effect will go away.

In a previous post I wondered why I had gotten faster at arithmetic over the previous six months. These data suggest that warm showers may be at least part of the reason. In Berkeley I take baths, not showers.

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17 Responses to Does Shower Temperature Affect Brain Speed?

  1. Pingback: Tweets that mention Does Shower Temperature Affect Brain Speed? | Quantified Self --

  2. Gordon Freeman says:

    I took the liberty of redoing your trend lines with better fitting:

    I think we have a breakthrough here.

  3. Teja says:

    I think it’s wrong that you base your decisions on just two experiments. Quantification is good, but the human body is incredibly complex, and I don’t think your math speed has anything to do with your cold water showers.

    • trench says:

      Obviously it could be a factor in why math speed decreased, but I agree… the series of tests are too simplified to give these results much merit.

      I do think it would be a fascinating subject to research under stricter conditioning though.

      • Mark says:

        Agreed. One simple but powerful reason for the observed relationships may be expectation. Seth went into the experiment expecting certain results – the results that he got. This could be countered by asking someone else to vary their shower temperature, tell them we’re interested in the effect of temperature on weight, and give them a whole bunch of tests ostensibly for another unrelated experiment, one of which is math speed. That way they won’t expect that temperature should affect math speed.

        Also note that the range of speed is very similar across all conditions. Statistical analysis would likely show that there is no difference between the conditions. More data might resolve that (and confirm that the observed trends are real).

  4. Luis Neves says:

    The book 4 Hour Body from Tim Ferriss recommends cold shower (and diet) as a way for fast loosing weight. I tried and it worked, but I really felt slow and dizzy.

  5. Tom says:

    That’s awesome :-)

  6. ian says:

    I think the benefits are extensive. I can’t comment on your results but my own experience of regular swims all year round including winter – down to 13º C here, show a stronger resistance to illness and ability to weather winters chill.

    Cheers Ian

  7. Seth Roberts says:

    Mark, I did not expect cold water to have any effect on my arithmetic speed.

  8. Nick says:

    Seth, I’m a big fan of your work, but in this case I’m extremely skeptical. You’re making a generalisation from a 20msec difference in calculation over a 500msec operation, without error bars, and have shifted the y-axis. How did you measure this? What is the expected error in measurement?

    I’m all for self experimentation, but this smells a bit like lying with graphs.

    • Seth Roberts says:

      How I measured this: Each measurement (each dot) comes from a session of about 40 arithmetic problems (e.g., 3+1, 7*2). I measured how fast I answered them and used only the correct answers to calculate an average for each session. I corrected for the difficulty of each problem so that difficulty was equated across sessions. Expected error in measurement: The standard errors of the averages are about 6 msec.

  9. Pingback: Shower effect | Selcycer

  10. Joe says:

    You are correct, Hot water dilates blood vessels so more blood can flow to brain whereas cold water constricts blood vessels so less blood can flow to brain. Your shower water should be of a mild temperature.

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  12. Pingback: Quantified dose | Selfabsorbed

  13. Dr Arbind Kumar says:

    It’s too early to conclude,particularly brain speed. Brain is a very complicated organ and a very well controlled experiment is needed to arrive any conclusion.

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