Concentration problems: what the research says (including the water thing)

In short: Yes, water matters. The effect is bigger than many people think. But water is only fourth on the list. Here's the full list.

Researched. Sources at the end.

"I can't concentrate." I hear this from founders very often. The usual answer is a productivity system.

Before you buy one, it's worth looking at the research. What actually makes concentration worse? Much of it is physical and boring. And boring things can often be fixed.

Here's the list. It's roughly in order of weight, as I read the evidence.

1. Sleep

In my view, this is the biggest lever on the list.

A meta-analysis looked at studies of short-term sleep loss. The largest effects were on simple and sustained attention. Working memory and thinking speed suffered too [1].

The tricky part: people who are short on sleep for a long time often barely notice their own decline [2]. You may feel less impaired than you are.

Is your concentration bad, and do you regularly wake up without feeling rested? Then start here.

2. Switching between tasks

Every switch from one task to another has a cost. You react more slowly and make more mistakes on the new task. This is measurable even when the switch was planned [3].

Founders switch all the time. It's part of the job. Part of the cost probably comes from the last task still lingering in your head.

What follows from this? Nothing dramatic, but something useful:

• A few long work blocks usually beat many short ones.
• Right after a switch, you are often slower than you think.

3. The phone on the desk

A widely cited set of experiments found this: just having your own smartphone nearby lowers your thinking capacity. Even when it's face-down, switched off and nobody uses it. The researchers measured working memory and the ability to solve new problems. Both were worse than in participants whose phone was in another room [4].

The authors call it "brain drain". Part of your attention goes into ignoring the phone.

The fix isn't willpower, it's distance. Put the phone somewhere else.

4. Water

This point surprises many people. So here is a bit more detail.

The big review. A 2018 meta-analysis pooled 33 studies with 413 participants. It appeared in Medicine & Science in Sports & Exercise. The result: dehydration makes mental performance worse. The clearest effects are on attention, executive function (planning and control) and coordination. The effects grow once the body loses more than about 2% of its weight [5].

How quickly you get there depends a lot on heat, activity and how much you drink. But you may notice effects earlier. Smaller studies suggest this.

The smaller studies.

• Young men: about 1.6% fluid loss was enough to worsen alertness and working memory. Tension, anxiety and fatigue went up [6].
• Young women: at about 1.4%, mood and perceived concentration got worse. Headaches increased, even at rest [7].
• A review in the British Journal of Nutrition concluded: the effects on mood and attention are consistent. On more complex tasks, the results are mixed [8].
• A small experiment: drinking water improved reaction time in people who were thirsty. In the others, nothing changed. So thirst itself seems to be a distraction [9].

The honest summary. Mild dehydration can make you feel worse, more tired and more anxious. It can measurably worsen your attention. It probably doesn't make you dumber on complex tasks.

That's already enough to care about. Attention and mood are exactly what you need for a hard afternoon.

How much? The European Food Safety Authority sets the adequate intake at about 2.0 litres of total water a day for women and 2.5 litres for men. Usually 20 to 30% of that comes from food [10].

Coffee probably doesn't count against you. In a controlled study, moderate daily coffee didn't cause dehydration in regular coffee drinkers [11].

And since thirst itself is a distraction [9], drink before it gets strong.

5. Movement

A single bout of moderate exercise brings, on average, a small improvement in thinking afterwards. The effect is strongest on executive functions, such as holding back and switching. It's clearest about 10 to 20 minutes after you finish [12].

The effect is small. But it's free. And it combines with everything above.

What this means in practice

Look at what's not on the list: motivation, mindset, the right app. Concentration depends heavily on your physical state. Yet many founders treat it as a character trait.

If your concentration is bad, work down the list:

1. sleep
2. the structure of your day
3. where your phone is
4. a bottle of water on your desk that's empty by lunch
5. a walk

That's not a productivity system. It's maintenance on your most important tool: yourself.

Have you done all of this, and concentration is still the problem? Then a proper conversation is worth it. Often the cause is then in how you work. If the problems persist, a medical check-up makes sense too.

References

1. [1] Lim, J. & Dinges, D. F. (2010). A meta-analysis of the impact of short-term sleep deprivation on cognitive variables. Psychological Bulletin, 136(3), 375–389. doi:10.1037/a0018883
2. [2] Van Dongen, H. P. A., Maislin, G., Mullington, J. M. & Dinges, D. F. (2003). The cumulative cost of additional wakefulness. Sleep, 26(2), 117–126. doi:10.1093/sleep/26.2.117
3. [3] Monsell, S. (2003). Task switching. Trends in Cognitive Sciences, 7(3), 134–140. doi:10.1016/S1364-6613(03)00028-7
4. [4] Ward, A. F., Duke, K., Gneezy, A. & Bos, M. W. (2017). Brain drain: The mere presence of one's own smartphone reduces available cognitive capacity. Journal of the Association for Consumer Research, 2(2), 140–154. doi:10.1086/691462
5. [5] Wittbrodt, M. T. & Millard-Stafford, M. (2018). Dehydration impairs cognitive performance: A meta-analysis. Medicine & Science in Sports & Exercise, 50(11), 2360–2368. doi:10.1249/MSS.0000000000001682
6. [6] Ganio, M. S. et al. (2011). Mild dehydration impairs cognitive performance and mood of men. British Journal of Nutrition, 106(10), 1535–1543. doi:10.1017/S0007114511002005
7. [7] Armstrong, L. E. et al. (2012). Mild dehydration affects mood in healthy young women. Journal of Nutrition, 142(2), 382–388. doi:10.3945/jn.111.142000
8. [8] Masento, N. A., Golightly, M., Field, D. T., Butler, L. T. & van Reekum, C. M. (2014). Effects of hydration status on cognitive performance and mood. British Journal of Nutrition, 111(10), 1841–1852. doi:10.1017/S0007114513004455
9. [9] Edmonds, C. J., Crombie, R. & Gardner, M. R. (2013). Subjective thirst moderates changes in speed of responding associated with water consumption. Frontiers in Human Neuroscience, 7, 363. doi:10.3389/fnhum.2013.00363
10. [10] EFSA Panel on Dietetic Products, Nutrition, and Allergies (2010). Scientific opinion on dietary reference values for water. EFSA Journal, 8(3), 1459. doi:10.2903/j.efsa.2010.1459
11. [11] Killer, S. C., Blannin, A. K. & Jeukendrup, A. E. (2014). No evidence of dehydration with moderate daily coffee intake. PLoS ONE, 9(1), e84154. doi:10.1371/journal.pone.0084154
12. [12] Chang, Y. K., Labban, J. D., Gapin, J. I. & Etnier, J. L. (2012). The effects of acute exercise on cognitive performance: A meta-analysis. Brain Research, 1453, 87–101. doi:10.1016/j.brainres.2012.02.068