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What are the effects of caffeine on the human body ?

Effects of caffeine on the body

This continues the topic about antinutrients, including:
What is an anti-nutrient ? and a list of common anti-nutrients.

Quick Re-cap of Definitions:

Caffeine is a common antinutrient that is found in coffee, tea and many soft drinks (incl. carbonated soft drinks that are popular with children).

Anti-nutrients (also written "antinutrients" and "anti nutrients") are substances - natural or synthetic, that interfere with the absorption and hence use by the body of nutrients such as vitamins, minerals, etc..

Caffeine is not an essential part of the human diet.

Some people choose not to consume any caffeine at all - in much the same way as some people choose not to consume alcohol, some people choose not to consume meat products, and so on. Although some religious groups and certain healthy eating philosophies discourage the consumption of caffeine, mainstream health advice does not generally advise against it's consumption in small quantities. In common with may other substances that are not harmful in modest amounts, caffeine is known to be have harmful effects if consumed in excessive quantities and can be fatal if ingested in extreme amounts.

Caffeine has a stimulant effect, and a diuretic effect (diuretic in the cases of people who are not used to it; regular users tend to develop a tolerance to the diuretic effect of caffeine). It is possible to develop a dependency on caffeine such that the body expects intake of caffeine and caffeine withdrawal symptoms may result if it is not consumed as usual.

 

General effects of caffeine on the body:

The effects of caffeine on the body, diagram by Mikael Häggström

In modest quantities, caffeine:

  • Stimulates the brain:
    • increasing alertness
    • causing some people difficulty sleeping
    • relieving fatigue (tiredness)
  • Stimulates respiration / increases respiratory action
  • Stimulates the kidneys - hence its diuretic effect!
  • Increases blood pressure and strengthens the pulse
  • Can act as an antioxidant

Caffeine can also:

  • Cause nervous over-reaction to stimuli incl. both psychological effects e.g. irritability and symptoms of anxiety, and physical effects such as reduced control of fine movements of the muscular-skeletal system e.g. as necessary for detailed craft projects.
  • Affect / disrupt the heart and arteries,
  • Affect / damage the lining of the stomach

The above mentioned effects are discernable but are not detrimental to most people unless caffeine is consumed in excessive (unsafe) quantities. Some sources describe the effects of caffeine on the body in terms of lists of "positive effects" and "negative effects" as shown.

Concern has also been expressed about the possible effects of caffeine in pregnancy. Some pregnant women reduce their caffeine intake or or avoid it altogether due to concern about the possibility of increased risk of miscarriage or birth defects.

 

Effects on the body of excessive quantities of caffeine:

Consumption of excessive quantities of caffeine can lead to caffeine overdose, also known colloquially as "caffeine jitters" and more formally as caffeine intoxication. Caffeine intoxication is a state of central nervous system (CNS) over-stimulation whose symptoms are similar to those of overdoses of other stimulants and can include more extreme:

  • restlessness / fidgeting
  • excitement / anxiety / irritability (emotional reactions)
  • insomnia
  • flushing of the face (due to increased blood flow)
  • increased urination (due to diuretic effect)
  • gastrointestinal disturbance (i.e. effects on the digestive system)
  • muscle twitching
  • verbal "rambling" e.g. semi-coherent flow of speech
  • irregular and/or rapid heart beat

In extreme cases of massive overdoses, symptoms may be even more severe and include:

  • mania / depression (i.e. more extreme emotional reactions)
  • disorientation / delusions / hallucinations / psychosis (i.e. disturbed perceptions)
  • rhabdomyolysis (breakdown of skeletal muscle tissue)

Ultimately, caffeine overdose can lead to death due to the effects of caffeine on the cardiovascular system - e.g. heart failure.



Effects of caffeine on nutrient uptake and requirements:

Excessive consumption of caffeine can result in some vitamins and minerals (or a proportion of them) that have been ingested into the body in food being excreted from the body rather than absorbed into it via the digestive system, including the gastrointestinal tract.


Drinking coffee within an hour of eating can reduce the absorption of:

  • iron (Fe)
  • magnesium (Mg)
  • zinc (Zn)
  • potassium (K), and other minerals
  • as well as some B vitamins.

The reported extent of the reduction in absorption varies widely in the range 40-80%, depending in part on when the meal and coffee were consumed, e.g. together or up to an hour apart.


Depending on the amounts of affected nutrients ingested (that is, if the person consumed enough to allow for a proportion of these nutrients to be "wasted"), the reduced absorption of them due to caffeine can lead to deficiency of some nutrients such as:


The nutrients mentioned above are necessary for, among other things, an effective immune system.
It has been suggested that excessive caffeine can adversely immune function in two ways:

  1. By reducing the availability to the immune system of important vitamins and minerals.
  2. Over-stimulation of the body due to caffeine can result in release of "stress hormones" e.g. cortisol, which prioritize short-term "flight or fight" instincts over longer-term immune function.

See also caffeine withdrawal symptoms, what is a balanced diet ?, dietary needs at different stages of life, and undernutrition.

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An introduction to the human digestive system

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