What it is
Caffeine is a non-energetic methylxanthine alkaloid.
What it does
Caffeine functions as a central nervous system stimulant that promotes wakefulness. It also has small but significant positive effects on most types of exercise performance (endurance, force output, power output, etc.).
It seems to exert these effects primarily by functioning as a central adenosine antagonist. Adenosine generally has inhibitory effects on the central nervous system. Caffeine keeps adenosine from binding to adenosine receptors in the brain, which increases alertness, reduces perceptions of pain and exertion, and increases motor unit firing rates.
For more on the molecular mechanisms and effects of caffeine intake, you may enjoy this article.
Recommended intake
Intakes of caffeine below 400mg per day generally don’t have any serious side effects, and aren’t associated with any long-term health consequences. In rare cases, caffeine toxicity can occur when individuals consume around 1200mg of caffeine in a short period of time, leading to seizures, though the average lethal dose is much, much higher. The average lethal dose of caffeine is estimated to be approximately 150-200mg per kilogram of body mass – 9,000-20,000mg for most adults. If you tried to consume that much caffeine from caffeinated beverages, you’d die of water toxicity before you died of a caffeine overdose, but it’s possible to accidentally consume that much caffeine from purified caffeine pills or powders. So, be very careful if you use an isolated caffeine supplement.
We figure most people want to enjoy the benefits of caffeine without suffering any serious side effects, so we generally recommend that folks should try to limit their caffeine to 400mg per day, and we definitely recommend against consuming more than 1,000mg of caffeine within the span of a couple hours. Though, if you’re particularly sensitive to the effects of caffeine, even 400mg might make you feel nervous and jittery. So, don’t treat 400mg/day as a universal top-end intake; your personal threshold might be quite a bit lower.
People who are pregnant or nursing are generally advised to limit their caffeine intake to a maximum of 100-200mg per day.
Likelihood of tracking completeness: Very low
Caffeine is not a nutrient that food manufacturers are required to disclose on nutrition labels. The vast majority of food manufacturers do not voluntarily list caffeine content on nutrition labels, so most branded products in the MacroFactor database lack information on caffeine. So, if you’d like to accurately track your caffeine intake, you’ll need to make a point of mostly tracking “common foods,” which come from research-grade databases that have full nutrient reporting.
For more on when you can track using branded foods versus common foods when you’re trying to accurately monitor your intake of particular nutrients, you should check out this article.
Likelihood of insufficient or excessive intake: n/a for insufficient intake, and low for excessive intake
You might feel like you need a cup of coffee to get out of bed in the morning, but caffeine is not an essential nutrient. Surprisingly, many people are in great health and function perfectly well without consuming any caffeine.
I’m not entirely sure how they accomplish this feat, but as a man of science, I must acknowledge that it’s physiologically possible.
Most adults consume less than 400mg of caffeine per day.
For more on nutrients with a greater likelihood of insufficient or excessive intake, you should check out this article.
Signs of deficiency/insufficiency: n/a
There’s no such thing as a caffeine deficiency. You’re not suffering from a caffeine deficiency because you didn’t have your morning coffee – those are withdrawal symptoms. Or, you just need to take a nap.
Good sources
Coffee, most teas, many soft drinks (including energy drinks), and chocolate all contain caffeine, and/or other compounds that are structurally and chemically similar to caffeine (like theobromine in chocolate). If you consume caffeinated beverages, be mindful of their added sugar content.