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Caffeine: Facts and Myths

By Chloe McLeon and Jess Spendlove, Advanced Sports Dietitians and Co-owners of The Health and Performance Collective.

Caffeine is the most widely consumed stimulant worldwide, for various reasons. With the wide consumption and interest in caffeine comes many myths – some true, some false.

Myth #1 Caffeine improves physical and mental performance
True – caffeine is a well-known enhancer of exercise performance and is one of the few supplements which has a strong evidence base for use in athletes. Caffeine largely improves exercise performance via reducing perceived effort and fatigue (i.e. makes exercise feel easier). This is because caffeine blocks a neurotransmitter called adenosine, which stimulates the central nervous system. This stimulation of the nervous system is also why caffeine can improve mental performance and alertness.

Myth #2 Caffeine can boost metabolism, burn fat and aid weight loss
True – caffeine has been found to boost Resting Metabolic Rate (RMR) by up to 11%, meaning more calories are burned at rest. Caffeine also increases ephinephrine (AKA adrenaline) levels, which stimulates fat breakdown, a process known as lipolysis. This is why caffeine is used in almost every ‘fat burner’ supplement. It is important to note that for caffeine to assist with weight loss and fat burning, it must be combined with exercise and a calorie deficit.

Myth #3 Caffeine and alcohol are safe to mix
False – alcohol and caffeine should not be consumed together, which is why alcohol mixed with energy drinks is a recipe for disaster. Caffeine is a stimulant and alcohol is a depressant, so when combined caffeine masks the depressant effects of alcohol. As a result, individuals may consume more alcohol and become more impaired by alcohol than they realise.

Myth #4 Caffeine consumption at night will impact sleep
True – caffeine impacts the sleep-wake cycle for most individuals to different degrees. It takes roughly 8-12 hours to remove caffeine from our bloodstream (highly variable between individuals). Therefore, it is recommended to avoid caffeine late in the day, to minimise the impact on sleep. It is important to note that not everyone responds to stimulatory effects of caffeine, which is why some people can have coffee late at night with minimal impact on sleep.

Myth #5 Pregnant women can’t consume caffeine
False – it is recommended pregnant women restrict caffeine intake to <200mg/d. This is because caffeine crosses the placental wall and can impact the foetus. Caffeine also inhibits iron absorption, an important nutrient during pregnancy. It has been found that limiting caffeine intake to <200mg/d during pregnancy poses no adverse health risks for the baby, which equals approximately 1-2 instant coffees.

Myth #6 Caffeine is bad for you
False – in fact, in appropriate amounts caffeine has been linked to various health benefits such as reduced risk of Alzheimer’s disease and Parkinson’s disease. Like anything excess intake can have negative effects such as diarrhoea, abdominal cramping, increased heart rate, insomnia, increased risk of osteoporosis (caffeine reduces calcium absorption/increases calcium excretion), anxiety and dehydration. Research suggests limiting caffeine consumption to <400mg per day, which equals approximately 2-4 instant coffees per day.