What Does Caffeine Do To You?


We are a society of tea drinkers, coffee connoisseurs and you only need to look around most work places to see people with a can of high caffeine soft drink on their desk but what exactly is caffeine and how does it effect us?


Caffeine is the most widely taken central nervous system stimulant in the world with caffeinated drinks forming a role in almost every culture on earth. For most of us in Western society it fulfills the somewhat paradoxical roles of being both a stimulating ‘pick-me-up’ and a common excuse for a relaxing get together with friends. Coffee in particular has escalated itself to almost cult status with new trendy ways to enjoy it popping up all the time. But how does our body respond when we drink our flat white, cappuccino or cold brew?


What happens when it enters our body?


It takes about 45 minutes for caffeine to be completely absorbed from the gut however absorption can start almost instantly through the lining of our mouths. Once in our blood it is rapidly moved around the body. Caffeine is also soluble in fats and this means it can travel across the ‘blood-brain’ barrier which also has a high fat content and this allows caffeine to exert its effects upon our central nervous system.


The peak level of caffeine in our blood is seen at around 75 minutes after ingestion.


Caffeine is ultimately broken down by the liver into several smaller molecules including Paraxanthine. This molecule seems to have similar actions to caffeine upon our blood pressure and fat metabolism however its peak concentrations occur much later (several hours) before being removed. This means that the effect upon blood pressure may continue long after ingesting caffeine- and may not fully subside if we are having a cup of coffee every few hours during the day. Paraxanthine is also thought to contribute to the development of caffeine tolerance and its withdrawal symptoms.


Eventually these breakdown products are removed from the body through our urine. Interestingly, smoking has been shown to increase the speed at which caffeine is broken down whilst there is evidence linking oral contraceptive use to slower caffeine break down.


What effects does caffeine have on our body?


Caffeine has been shown to affect fine motor coordination through interfering with the movement of potassium and sodium through cell membranes in the body (shaky hands anyone??). This may mean that for people performing delicate tasks that caffeine is not a good idea!


Caffeine stimulates the heart and causes both an increase in heart rate and because of this an increase in the demand the heart muscle has for blood- therefore for people who are known to have problems with the blood supply to the heart such as people with angina or who have had heart attacks in the past, caffeine may put them at an increased risk.,


When caffeine reaches the lungs it causes a relaxation of the muscles in the airways- this allows them to open wider and for more air to enter the lungs with each breath. It is thought that this may be beneficial to people who suffer with asthma. Further to this, Theophylline- another breakdown product of caffeine is also used a drug in inhalers.


In the kidneys caffeine has the effects of causing ‘diuresis’- making us produce more urine. Though most caffeinated drinks are more hydrating than they are dehydrating, this is obviously less than ideal if you are perhaps already dehydrated or about to perform an activity that may cause dehydration, especially if you prefer ‘espresso’ type short, strong drinks. Further more, be careful of drinking caffeine if you are about to find yourself in a situation where getting to a toilet may be difficult or if you already suffer with struggling to get to the toilet on time.


In exercise, the American College of Sports Medicine report found the evidence was mixed, however that overall the research supported caffeine having a performance enhancing effect on performance. For endurance activity recent research found ingestion of 3-5mg/kg of caffeine one hour prior to exercise enhanced performance without causing side effects. For short duration, high intensity exercise lasting approximately 5 minutes, ingestion of caffeine seemed to improve performance- however more research is needed in this area. They concluded that ingestion of 3-5mg/kg of coffee may enhance performance and should not cause either side effects or an illegal blood-doping profile.


When it comes to mental performance there is alsot of research of mixed quality and some conflicting data however it appears that there are trends that emerge. Caffeine ingested at levels between 150mg and 250mg seems to speed up reaction time, problem solving and improve alertness (especially during menial tasks)  however high concentrations resulted in anxiety and mood problems. There also did not seem to be a ‘tollerance’ built up by regular caffeine use with regarnd to mental performance enhancement. There was however much debate amongst the research and certainly more robust research is needed in this area.


So, Should I drink caffeinated drinks?

The decision whether or not caffeine is a good idea to drink falls down to you as an individual. Certainly there are people for whom limiting caffeine may be a good idea- those with heart problems, raised blood pressure and bladder instability in particular. For the majority of us however, enjoying a cup of tea or coffee with friends is an important part of our social lives and the benefits to our mood must not be overlooked. Caffeine may also have some performance enhancing effects upon our mental and physical activities- though it is becoming obvious through conflicting research in both these areas that other factors may be at play- in particular individuals differences. It is also worth noting that both areas of research found performance degrading or unsafe side effects at higher doses.  Ultimately I think it is a case of finding what works well for you- Sip it and see!


Caffeine for the Sustainment of Mental Task Performance: Formulations for Military

Operations. Institute of Medicine (US) Committee on Military Nutrition Research.

Washington (DC): National Academies Press (US); 2001.


ACSM Current Comment  Lawrence L. Spriet, Ph.D., FACSM (Chair) and Terry E. Graham, Ph.D., FACSM. Accessed https://www.acsm.org/docs/current-comments/caffeineandexercise.pdf



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