The gut feeling about caffeine

 Following from my previous caffeine post: What are the effects of caffeine on our bodies? I thought it's time to round off my investigation into the intriguing substance of caffeine.

Not the best way to find out the effects of caffeine on the body

Do you ever get that gut feeling when drinking coffee?-Coffee and the gastrointestinal system

There is strong evidence that coffee increases gastric acid secretion. Interestingly experiments have shown that it's the other constituents in coffee that contribute to this increase in gastric acid secretion.
This was shown by  measuring the dose response of caffeine, regular coffee and decaffeinated coffee for gastric acid secretion in normal subjects. Both regular coffee and decaffeinated coffee gave a similar response in gastric acid secretion which was higher than that of caffeine alone (on a cup equivalent basis) (Cohen and Booth, 1975).

The dose response? what??

Measuring the dose-response enables scientists to observe the change in an effect (in this case:gastric acid secretion) caused by varying the levels of dose of a substance (in this case: dosage of caffeine, regular coffee and decaffeinated) after a certain length of time.

Kidney function

The kidneys play an important role in filtering the blood. The kidneys remove waste products (such as urea) and extra water from the blood which form urine. Any drinker of caffeine beverages is well aware that caffeine tends to stimulate an increased flow of urine.

Anatomy of Kidney

Caffeine was traditionally used to increase urine output until more potent diuretics became available. The diuretic effects of caffeine appear to be due to an increased rate in blood flow to the kidneys and increased rate of blood filtration. These affects are due to antagonism of circulating adenosine (see previous post) having a regulatory role in the formation of urine  (Fredholm 1984).

So will my cup of coffee cause a fluid imbalance?
A dose of 300mg of caffeine (approximately 4-5 cups) can cause acute diuresis- this has been shown by several studies (Oswald and Schnermann., 2011). Caffeine will only cause a significant increases in the volume of urine excretion and a negative fluid imbalance in a large dose. A study in which caffeine was given (6mg/kg) for 11 days showed no effect in daily urine volume (Armstrong et.al 2005).

Time for a breather-Respiratory system

Caffeine is a respiratory stimulant (Braun 1996). However based on the average person's caffeine consumption has little effect on the respiratory system. Larger doses of caffeine has proven to be effective in the treatment of neonatal apnea-the cessation of breathing in newborns.

Upcoming posts

How about  I keep it a surprise this time?

References

Armstrong LE, Pumerantz AC, Roti MW, Judelson DA, Watson G, Dias JC, Sokmen B, Casa DJ, Maresh CM, Lieberman H, Kellogg M. 2005., Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption. Int J Nutr Exerc Metab. 15

Braun S., 1996., Buzz: The Science and Lore of Alcohol and Caffeine., Cary., NC., USA., Oxford University Press
., 252-265. Cohen, S., and Booth, G. H. 1975., Gastric acid secretion and lower-esophageal-sphincter pressure in response to coffee and caffeine., New England Journal of Medicine., 293,897-899.

Fredholm, B. B., 1984.,Cardiovascular and renal actions of methylxanthines., New York:Alan R.Liss

Oswald H and Schnermann J., 2011., Methylxanthines and the Kidney., Handbook of experimental pharmacology., 200., 391-412.

What are the effects of caffeine on our bodies?

An advertisement in a London newspaper in 1657 described coffee as: "A very wholesome and physical drink that helpeth digestion, quickeneth the spirits and maketh the heart lightsom, is good against eye-sores,coughs, colds, rhumes, dropsie, gout and scurvy." (Braun S., 1996)

Obviously today we do not view coffee and caffeinated substances to be this marvellous medical elixir.

So what are the effects of caffeine on the different systems in our bodies?

I'll be starting with the nervous and cardiovascular systems

Nervous and cardiovascular systems

Caffeine and the nervous system

Caffeine is a central nervous system stimulant-It increases brain and spinal cord activity, speeding up physical and mental processes.

Caffeine also affects the autonomic nervous system -A branch of the peripheral nervous system which controls smooth muscle, internal organs and glands (click for more information on the nervous system).
There has been reports that caffeine increases skin conductance (sweat gland activity). A 500 mg anhydrous (dry weight) caffeine dose can produce behaviour similar to General Anxiety Disorder also referred to as 'caffeinism' (Bruce et al., 1986). Caffeinism is a condition resulting from ingestion of a large dose of caffeine shown by diarrhoea, elevated blood pressure, restlessness and insomnia.

Putting things into perspective: a 500 mg dose all at once is a large amount considering  an average cup of instant (heaped tea spoon) coffee contains 60 mg (Center for science in the public interest., 2012). A large dosage of caffeine can produce extreme symptoms due to the rapid rate at which  caffeine is absorbed. So do not fear drinking your morning cup of coffee as 500 mg is a high dose and was used for experimental purposes.

Note how some of the effects caffeine has on the nervous system appear anxiety reducing (i.e increasing concentration and reducing tiredness) and some effects similar to anxiety (insomnia and restlessness).

Cardiovascular system

 Caffeine has an interesting effect on blood flow. In moderate amounts caffeine can increase blood pressure-the effect is more significant in those who do not regularly consume caffeine (Bruce., 1986: James 1997). But surprisingly has little effect on heart rate (France and Ditto 1992).

How does this change in blood flow come about?
Caffeine molecules compete with adenosine for adensosine receptors on cardiovascular cells (See previous post on receptors). In the cardiovascular system adenosine causes dilatation of coronary and cerebral blood vessels. Caffeine inhibits this process, meaning the blood vessels remain constricted. The narrower diameter of the blood vessels result in higher blood pressure (James 1997).

Time for a little analogy......
Imagine you have gone shopping for a new garden hose. Your standing in the aisle looking at the different diameters of garden hoses you can buy. Whilst you do this you imagine watering your garden with your new hose. The pressure of the stream of water coming out of the end of the hose depends on the diameter of the hose. Logically the narrower the diameter of hose the higher the pressure.

Hoses varying in diameter

Like hoses our blood vessels are the same. The narrower the vessel the higher the blood pressure in that vessel. But blood vessels (unlike your garden hose) are clever and can change diameter.

When adenosine is present in the blood, this causes the smooth muscle in the blood vessels to relax- the vessel wall gets thinner and the space where blood flows in the vessel gets wider: this is vasodilatation. When caffeine is present and binds to adenosine receptors instead of adenosine; it has the opposite effect. The smooth muscle in the vessel wall contracts and gets thicker so the space where blood flows gets narrower resulting in a higher pressure in that vessel: this is vasoconstriction.

Upcoming posts....

I'll be looking at the physiological effects of caffeine on the gastrointestinal and respiratory systems and also the effect on renal function (think peeing!). I also hope to do a bit about caffeine and health.

References

Braun S., 1996., Buzz: The Science and Lore of Alcohol and Caffeine., Cary., NC., USA., Oxford University Press

Bruce M, Scott N, Lader M, Marks V., 1986., The psychopharmacoloical and electrophysiological effects of a single dose of caffeine in healthy human subjects., British Journal of Clinical Pharmacology., 22, 81-87., [Online]., Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1401080/?page=1 ., [Accessed: 02/10/2013].

Center for science in the public interest., 2012., Caffeine content of food & drugs (online)., (Updated 2012)., Available at: http://www.cspinet.org/new/cafchart.htm., [Accessed: 03/10/2013].

France C and Ditto., 1992., cardiovascular reponses to the combination of caffeine and mental arithmetic, cold pressor and static exercise stressors., Phychophysiology., 29., 272-282.

James J., 1997., Understanding Caffeine., California., USA., SAGE Publications Inc