The exercise habit that causes heart attacks: Millions of people make the same mistake

O'Reilly, who made remarkable statements in a post he made on his TikTok account, said, "Pre-workout powder supplements usually contain more than 300 mg of caffeine in a scoop or serving. This is equivalent to drinking three cups of coffee at once. In case of unconscious consumption, intense anxiety, tremors and heart palpitations can be seen in the person."

O'Reilly added that as a natural pre-workout alternative, eating a banana 30 minutes before exercise will provide enough energy.

Experts have long pointed out the dangers of consuming high doses of caffeine, especially in individuals with undiagnosed heart rhythm disorders.

Caffeine causes the release of hormones that increase heart rate and blood pressure, which can trigger a rapid heartbeat known as atrial fibrillation in some susceptible individuals.

O'Reilly's warning comes after a similar notice was issued last year by the UK Food Standards Agency (FSA), which warned the public about the dangers of such products after a 29-year-old man suffered a fatal heart attack after taking the wrong dose of caffeine powder.

Personal trainer Thomas Mansfield died in January 2021, just hours after consuming a concoction containing seven times the recommended daily amount of caffeine. He began foaming at the mouth shortly after drinking the concoction and collapsed to the ground clutching his chest. An inquest found Mansfield had taken almost 16 times the maximum recommended dose on the packet. The FSA said this was equivalent to around 200 cups of coffee.

Even more worryingly, according to FSA figures, less than half of people read the dosage instructions on such supplements.

The Food Standards Agency has warned that daily caffeine intake should not exceed 400mg, which is equivalent to around four cups of coffee.