Caffeine and exercise: Part 1
This is part 1 of a 3 part article about caffeine, focusing mainly on the physiological mechanisms of caffeine and its usage during exercise.
If there is one thing that can be shared across nearly every country and nation, it is our love of caffeine. Caffeine is one of the world's most used drugs, ranking just behind alcohol and tobacco, with over 90% of the world's population consuming it daily. Its immense popularity has made it a remarkably well studied substance, with its physiological mechanisms being well known.
Physiological effects
Caffeine falls into the xanthine chemical group, which includes adenosine, and works by antagonising (activating) adenosine receptors - To our nerve cells caffeine looks a lot like adenosine which allows it bind to our receptors. As adenosine causes sedation and relaxation when it acts upon its receptors, through preventing this binding, caffeine instead results in alertness and wakefulness. While how quickly caffeine reaches your bloodstream depends on method of ingestion (pure caffeine is absorbed far quicker than coffee of example), on average it reaches peak serum (in blood) concentration an hour after ingestion with a half-life of 6 hours, meaning it takes 12 hours to be removed entirely from our body.
If you’ve ever had a strong coffee you’ll be familiar with the most common side effects, increased wakefulness, decreased appetite and for coffee naive people (people who haven’t built up a tolerance) even euphoria. As well as those more obvious symptoms caffeine also caused the following:
Vasoconstriction (constriction of blood vessels)
Increased blood pressure
Raises plasma levels of adrenaline and noradrenaline
Decreased appetite
Tremor
Increased respiration
Calcium ion mobilisation (a risk factor for osteoporosis)
Before you panic about the last one, keep in mind that while caffeine-containing beverages have been associated with bone mass reduction and increased fractures, these effects were found to be offset by as little as 1-2 teaspoons of milk.
Nootropic effects
Despite the common belief that caffeine allows you to perform above and beyond your baseline, the research is indicating otherwise. When tested in both well rested and fatigued individuals where both were given identical amounts of caffeine, there was an increase in the fatigued group's cognition and reaction time, but actually a decrease in the well-rested. It appears that in tired individuals, caffeine allows people to return to their baseline, but not above it, as shown in the well-rested group. It manages to return tired individuals to baseline through its ability to directly interfere with our bodies adenosine receptors, which play a large role in regulating sleep.
Excessive usage
While in Australia we don’t currently have any guidelines for recommended daily intake, the majority of regulatory agencies worldwide consider a daily intake up to 400mg to be safe for the average adult, however, pregnant women require special consideration (dosages up to 200mg a day).
While the majority of users spread out their intake throughout the day even in those who used high, acute doses of up to 3mg/kg (210mg for a 70kg male) are unlikely to induce clinically significant changes in resting blood pressure, myocardial blood flow, hydration status or thermoregulation.
Take home message
Caffeine is one of the most well researched supplements and is considered to be safe to use (check with your physician before starting any supplementation)
Caffeine doesn’t appear to have a nootropic effect
Try to avoid having more than 400mg of caffeine a day
Having a little bit of caffeine daily (through supplementation or diet) is enough to buffer the effects of caffeine on bone health