Side effects of Caffeine

Caffeine is the most popular supplement and widely used drug in the UK and US with an estimated 90% of adults using caffeine every day (New Scientist, 2013). Because of this Coffee shops are everywhere! (1500 Costa Coffee shops in the UK). Caffeine is classified as a thermogenic, which means it’s designed to stimulate metabolism, and therefore increase energy expenditure and promote weight loss (Kreider et al, 2010).  

Caffeine is primarily degraded in the liver. Between 0.5-3.5% of the caffeine you ingest is not degraded and is excreted in urine. According to Kovacs, Stegen & Brouns (1998) it can also be excreted via sweat. Caffeine supplementation has a number of effects on the body, these effects include the stimulation of lipolysis, stimulation of catecholamine release, and the release of dopamine and B-endorphins. Caffeine can also influence carbohydrate metabolism, and increases calcium release.

Beverage/Product Amount Caffeine (mg)

Coffee, generic brewed 350ml 200mg
Tea, brewed 350ml 80mg
Coke/Pepsi 350ml 35-38mg
Monster (Can) 454ml 160mg
Red Bull (Small can) 240ml 80mg
Rockstar (Can) 480ml 160mg

Studies have reported strong benefits of short-term increases in metabolic rate of between 3-16% following a 100-400mg dose of caffeine, this is a big difference to the person trying to lose weight. Looking further into the evidence, a study performed by Bridge & Jones (2006) found that a dose of 3mg per kg of bodyweight (240mg for an 80kg person) resulted in a 23.8 second faster 8km run under race conditions.

As with anything very high-dose caffeine consumption could have potential side effects, the short/long term side effects could include.

Short Term

⦁ Insomnia
⦁ Headache
⦁ GI irritation/bleeding
⦁ Stimulation of diuresis
⦁ Muscle tremor
⦁ Impaired co-ordination
⦁ Tachycardia (resting heart rate of above 100bpm)
⦁ Higher blood pressure

Longer term

⦁ Bladder cancer? (Side note) In research the opposite effect has also been reported with caffeine intake and the reduced risk of bladder cancer (Sala et al, 2000). 
⦁ Ulcers
⦁ Seizures
⦁ Coma
⦁ Death

Caffeine has now become more widely used and accepted as a supplement in competitive and elite sports.

As suggested in the study performed by Bridge & Jones (2006) the recommended dose of caffeine for performance and focus purposes is around 200-240mg per day for an 80kg person. If you wish to supplement your diet with caffeine, begin with this dose initially and reduce if short-term side effects are experienced. If you’re unsure about supplementing your diet with caffeine or you are worried about how this may affect your medical history, consult your GP for advice.

It’s important to remember when supplementing your diet with caffeine for performance and/or weight loss purposes, to have a rest period from using it, your body adapts quickly to what it takes in and before you know it that 1-2 cups of coffee a day has turned into 5-6 to get the same ‘buzz’ from it.

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