Caffeine is a commonly found in coffee, certain teas, cocoa, soft drinks, and energy drinks, and is known for its ability to increase alertness and the feeling of being awake when ingested. More recently, it has become popularly used as caffeine powder as part of pre-workout supplements to increase focus and energy. These pre-workout supplements claim that caffeine can improve mental alertness, memory, exercise performance, and increase the ability to burn fat. While studies have shown that 0.09 g to 0.15 g of caffeinated coffee per kilogram of body weight can improve workout performance, pre-workout supplements can range from 150 mg to 300 mg of caffeine per serving. This means each serving of pre-workout contains caffeine equivalent to up to three cups of coffee, which could make it easier to reach toxic doses.
Toxicity and Adverse Effects
Common side effects of caffeine include:
- Feeling more awake and alert,
- Restless,
- Anxious,
- Irritable,
- Increased body temperature,
- Dehydration,
- Headache, and
- Faster breathing and heart rate
However, at toxic ranges of caffeine more extreme and dangerous adverse effects can occur. Some symptoms of caffeine overdose include:
- Very fast or irregular heartbeat,
- Shakiness,
- Feeling sick or vomiting,
- Confusion, and
- Panic attacks
Caffeine’s non-selective adenosine receptor antagonist activity, phosphodiesterase inhibitor activity, and cholinergic activity through the inhibition of acetylcholinesterases, causes the variety of adverse effects seen with toxic doses. This activity can cause coronary vasospasm and vasoconstriction, which will increase heart rate and blood pressure, and can cause arrhythmia. In extreme cases, caffeine overdose can even cause death by ventricular fibrillation. This is when the lower chambers of the heart do not contract regularly and instead vibrate, causing cardiac arrest.
Safety
Even at non-toxic doses, the combination of increased heart rate due to caffeine and the stress from cardiovascular work outs can put unnecessary strain on the heart. The FDA warns that a teaspoon of powdered caffeine that is used in pre-workout supplements can have as much caffeine as 28 cups of coffee. This is much higher than the dietary guidelines which say that adults should not consume more than 400 mg of caffeine a day, which is equivalent to between three to five 8-ounce cups of coffee.
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