Caffeine – Friend or Foe?


Caffeine – Friend or Foe?

For the first 19 years of my life I didn’t touch tea or coffee. It never appealed to me, despite my parents and brother being avid tea drinkers. That all changed in 2013 when I was preparing to sit my first set of summer exams with UCD. I learned quickly that coffee not only was very tasty but was exactly what I needed to get me through the study hours. Since then, I’m a daily coffee drinker. And you know what? There’s not a thing wrong with that. However, it is worth considering how, when and why we consume (or sometimes rely) on caffeine.

Caffeine & Sleep

Many people drink coffee to stay awake, be that for a long car journey late at night or to work into the early hours on assignments. It is understood that caffeine will begin to affect sleep when 100mg or more is consumed, especially when close to bedtime – see table 1 for amount of caffeine in commonly consumed foods and beverages.

Caffeine has a half-life of seven hours, meaning that it stays in the body for 14 hours after it has been consumed. While this is great during exam season, if we overly rely on caffeine and don't get enough sleep, over the long-term it can affect more than just our mood and productivity. Lack of sleep and poor sleep quality over an extended period can increase the risk of non-communicable diseases such obesity, type 2 Diabetes, depression and anxiety.

If you have trouble sleeping and find that you rely on caffeine to counteract this lack of sleep, consider other factors that may be keeping you awake plus your overall sleep hygiene. This includes sleeping in a clutter-free, tech-free bedroom and adopting a sleep schedule, e.g. reading or meditating before bed. If you feel your sleep issues are getting out of control, speak to your GP.

Caffeine & Hydration

The general rule of thumb that many of us grew up with is to drink 2L or 8 glasses of water per day. There is a belief that tea and coffee can't count towards your total fluid intake. Yes, caffeine (found in tea and coffee) acts as a diuretic. However, you must remember that every cup/mug of tea or coffee contains anywhere from 150-500ml water, depending on what size of a vessel you choose to drink from. Therefore, as these drinks are over 85% water, they are deemed to count towards total daily fluid intake, according to the British Dietetic Association.

Caffeine & Sports Performance

Caffeine is a stimulant, propelling the body further, reducing the perception of fatigue and stimulating bodily functions such as the bladder and the bowels. The latter is worth remembering if you decide to experiment with the potential benefits of caffeine in relation to sports training – don’t try anything new on race day, as the age old saying goes. For sports performance, athletes may choose caffeinated drinks, gels or simply a black coffee.

The effect of caffeine is believed to peak 40 minutes after intake and may be something worth thinking about if you decide to use caffeine before a long run or cycle. I personally am a big fan of caffeine pre-race. Although I am willing to admit that it may be the placebo effect as much as anything else. The main message here is to get to know your body and what works for you, regardless of it being placebo or not.

At present, there is no evidence to suggest that the general population should stop drinking tea or coffee. In 2015, the European Food Safety Authority (EFSA) concluded that, except for pregnant women, single doses of caffeine up to 200mg or daily consumption of 400mg is safe – see table 1 for caffeine levels in commonly consumed foods and drinks.

Food/BeverageCaffeine Content
Mug of tea50mg
Mug of coffee90mg
250ml energy drink80mg
Can of cola40mg
50g dark chocolate25mg
50g milk chocolate10mg

Table 1: Caffeine content of commonly consumed foods and beverages:

NB: Caffeine content in coffee and chocolate can vary depending on the manufacturing process, raw ingredients, product composition and other factors.

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