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The calculus of caffeine consumption - Arvind Narayanan's journal [entries|archive|friends|userinfo]

The calculus of caffeine consumption [Apr. 16th, 2007|04:33 am]
Arvind Narayanan
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Considering the huge role that caffeine can play in enhancing (workplace) productivity, it is worthwhile to study its effects and mechanism with the hope of maximizing this productivity-enhancing effect. I've done the legwork for you, so sit back and read. The results might surprise you.

Mechanism. Caffeine has a number of effects on the body, but the one that is relevant here is that it blocks adenosine receptors in the brain (by tricking your brain into thinking it is adenosine.) A decrease in the activity of adenosine (which is a sleep chemical) increases neuron firing rate and increases focus and concentration.

Caffeine tolerance builds up rather quickly (2-3 weeks) and further, is near-total. That means that if you drink coffee regularly, pretty soon you start producing more adenosine in respose; thus you need your caffeine dose just to get up to your normal level of brain activity, and you're dopey if you don't take it. Another way to think about it is that the time-average of adenosine level (and hence, attention level) tends to stay more-or-less constant, both short term and long term.

Short term strategy. Let us examine the way that most people take caffeine -- when they feel sleepy (I will call this antagonistic consumption.) This changes the attention level from the green line to the blue line (i.e, it smooths out the fluctuations.) This works great for many people (say, someone that has a data entry job), because maximum productivity is limited by external constraints. Other jobs where antagonistic consumption is essential include assembly line worker and truck driver, where mistakes can be disastrous but there is little to be gained from peak concentration.

Daily fluctuation in attention level, highly oversimplified. The green line represents no coffee. The blue line is antagonistic consumption. The red line is reinforcing consumption.

But other jobs, often characterized by a low level of repetition, have a markedly different attention-productivity curve. Academic research, for instance, involves generating ideas that no one has come up with before. Clearly, an idea that advances the state of the art is unlikely to occur except when attention level peaks. If you spend your entire day doing nothing, but all that doing nothing somehow enables you to reach a point where you understand your research problem well enough that you get insights that no one ever did before, then that's good research. Writers are another example: it is common to sit around for days or weeks waiting for inspiration to hit ("writer's block").

What is common to these tasks is that progress happens in spurts, due to the fact that they involve frequent cognitive bottlenecks. A cognitive bottleneck can only be overcome when attention level exceeds a task dependent, typically very high threshold. Clearly, then, antagonistic caffeine consumption results in worse-than-normal productivity, because it flattens the attention level curve and decreases the fraction of time spent at peak attention level. Instead, reinforcing consumption helps maximize productivity (the red line). According to this strategy, the best time to drink coffee is when you are already very alert.

Productivity as a function of attention level for naturally rate-limited tasks (green line) and tasks with cognitive bottlenecks (blue line). The former is concave and the latter is convex.

A job like driving trucks is one end of the spectrum, where productivity is naturally and insuperably rate-limited. Jobs with frequent cognitive bottlenecks like at the other end. In each of these cases, the optimal pattern of caffeine consumption is clear. Most other jobs fall somewhere in between, and each person must make a reasoned decision about what works best for them.

Sleep. The reinforcement strategy has another element to it. When adenosine peaks, the best response is not to fight it, but "go with the flow" and (shock, gasp) sleep.  Sleep has effects on memory consolidation and is extremely beneficial in overcoming cognitive bottlenecks, making the brain maximally alert right after waking up. Thus, a possibly very effective coffee drinking pattern would be two cups a day, one early in the morning and one right after an afternoon nap. (Unfortunately, napping is stigmatized in the Western work culture, despite much scientific evidence touting the benefits. I hear that such stigmatization is non-existent in China. Good for them.)

Long term strategy. Over the long term, consistent caffeine consumption is as good as nonconsumption, because of (you guessed it) tolerance. Is there a better strategy? Of course there is. Periodic abstinence lets adenosine levels return to normal. With complete abstinence, it takes 5 days to reach adenosine normality; conservatively, and with imperfect abstinence, a week or 10 days may be required. (Quitting is hard!) For most people, work involves a natural cyclic pattern of crunches and lean periods, and  moderated coffee consumption to reflect this pattern will let you enjoy its cognition-enhancing effects more-or-less permanently.


1. Many products contain caffeine, especially sodas. Carelessness about extraneous caffeine sources will diminish the effect that well-planned coffee-drinking can have. (Of course, the sugar in sodas is far more harmful than the caffeine, so that would probably be the least of your worries.)

2. Personally, since I discovered these principles 6-8 months ago, I've had an absolutely unbelievable time in terms of research productivity. I've also had 3-4 quitting cycles in this time period (which is less than ideal, but I didn't realize the importance of quitting until later.)

3. There appears to be a generally low awareness of cognition-enhancing substances in general, such as creatine. I plan to expand on this in a later essay.

4. This essay (and everything else I write on this blog, unless otherwise stated), is licensed under CC-by-SA.


From: (Anonymous)
2009-10-01 10:58 pm (UTC)

Does sugar plus vitamin supplementation still cause empty calory "leaching?"

I think your article on Caffeine is great. That's why I am confused by your stance on sugar. Your the first person I've found who really seems to understand caffeine (I did my grad work in psychology in the neuroscience department at Baylor U. where I learned a lot about caffeine). Everything I learn about table sugar from scientific sources seems to point to it as a relatively low GI food (65 on average) relative to things like potatos and white bread. Since every form of food eventually gets turned into sugar, I don't see what the problem is as long as you make up for the deficiency of vitamins and minerals with suplements and other green/colorful foods.

I've always thought that all the anti-sugar stuff was a bunch of moms with nothing better to do or nutritional experts trying to scare people into buying their consultation services. But since I respect your scientific scrutiny on the issue of caffeine, I'd like to ask you a question.

Why would a high table sugar diet be worse than a high white-potato diet if you took a supplement that made up for the missing potassium and fiber that is found in potatoes? Since potatos have a high Glycemic index and that has been associated with diabetes and heart disease, I'm thinking a Snicker's bar or peanut M&M's (both extremely low GI) are one of the healthiest foods for a person to eat if you add some fiber and vitamins/minerals from other sources.
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[User Picture]From: arvindn
2009-10-03 06:24 am (UTC)

Re: Does sugar plus vitamin supplementation still cause empty calory "leaching?"

hey, thanks for your comment, i will answer this in a day or two.
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[User Picture]From: aredridel
2010-07-09 04:38 am (UTC)

Re: Does sugar plus vitamin supplementation still cause empty calory "leaching?"

I'm not sure that the two diets are terribly different. The research I've done on sugars definitely points to problems with, say, a high-potato diet.

The confounding thing is that the quality of carbohydrates matters as much as which ones: how they're prepared, what they're eaten with. In the American Journal of Clinical Nutrition's lated glycemic index table, there's variation between glycemic index (compared against pure glucose) of 50 points between glucose alone and glucose fed with oat fiber. (Am J Clin Nutr Foster-Powell et al. 76 (1): 5.)

There are definite interlinks between serotonin receptors (which can affect depression and various other mental states) and carbohydrate digestion. A lot of these things play together.

I know from personal experience that I suffer less eating potatoes than sugar -- but I never eat just potatoes. They're always fried, mixed with meat, or with other vegetables. Sugars, when I eat them, tend to be mixed with white flour or made into a syrup as in sodas.

The other part of the puzzle is that glycemic index doesn't measure insulin response: Fructose will trigger an insulin response, but insulin doesn't do much with fructose. The effect can desaturate the serotonin receptors in the gut and various other metabolic responses. What sugars, with what, can matter a great deal.

So the usual advice for diet goes: "Eat a good variety. Mostly plants. And not too much."

"Leaching" would be just your body running, assuming it has the full input it needs, getting the raw calories and giving the metabolic processes the full go-ahread, without actually having anything but the actual energy content to go on.

So yeah, eating an all-white diet could do that.

As far as alertness, my optimum combination is coffee relatively early, brief exercise to get my heart rate up, then working, while eating a diet of small meals, mixed vegetables and some starches. (Brown rice or whole-grain bread) -- six small meals a day works better for me than three larger ones, by far.
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