Humans Have been consuming coffee for over 2,000 years. Its ingredient caffeine raised questions about its health effects. Early studies involving bacteria and cultured mammalian cells suggested that caffeine could be harmful. Further, the cells exposed to ultraviolet light and then treated with caffeine, showed an increase in damage. By 1960s, coffee came to be regarded as slightly harmful.
The case of coffee as a harmful dietary agent would have been closed, but for an accidental discovery in 1971 in my laboratory at the Jawaharlal Nehru University (JNU), New Delhi.
The experiments then designed were to find out how caffeine enhances radiation-induced biological damage. The choice of barley seeds due to lack of facilities then to work with mammalian cells turned out to be a blessing. It is known that biological damage induced by X-ray and gamma rays is increased by oxygen.
In fact, the reduced levels of oxygen in rapidly growing tumours is responsible for the resistance of cancer cells in radiotherapy.
In barley seeds methods were developed to separate the radiation-induced, oxygen-dependent (oxic) pathway from the oxygen- independent (anoxic) pathway of damage.
Caffeine was expected to enhance both the oxic and anoxic components of radiation damage.
However, caffeine remarkably reduced (protected) the seeds against the oxic pathway of radiation damage, although it potentiated the anoxic component of damage.
The focus became the radiation protective mechanisms of caffeine when oxygen is present in the cells. It had already been known that development of radiobiological damage involves sequential events ranging in time span from 10-14 seconds to hours, days and years.
Also well established was that ionizing radiations eject electrons from the atoms and molecules and produce electrically neutral, highly-reactive, short-lived entities known as `free radicals'.
For example, water molecules exposed to gamma-rays break down into hydrated electrons, hydrogen radicals and hydroxyl radicals. The hydrogen radicals and hydroxyl radicals are electrically neutral unlike the hydrogen ions and hydroxyl ions, which have positive and negative charges respectively. The hydroxyl radicals can abstract electrons from DNA and other cellular macromolecules, and cause damage.
The hydrogen radicals and hydrated electrons also react with oxygen to form highly damaging entities called hydroperoxide, superoxide anion and hydrogen peroxide. The products of reaction of free radicals with oxygen are referred to as `reactive oxygen species' (ROS).
Besides ionizing radiation, certain chemical agents, dietary substances, several physiological and metabolic processes in the biological systems also lead to the generation of ROS. So, ionizing radiations are not unique in producing ROS. Considerable protection from the damaging action of ROS is exerted by dietary substances which scavenge the free radicals and the ROS.
Our studies have revealed that caffeine effectively scavenges off hydroxyl radicals and it outcompetes oxygen in reacting with electrons and prevents the formation of ROS.
So, the fundamental mechanism of radioprotection by caffeine involves neutralizing/elimination of the ROS. Hence, it is expected that caffeine would reduce the risk to the free-radical and ROS-mediated diseases whether cardio-vascular, diabetes type 2, arthritis or cancer etc. The scientific literature covering hundreds of carefully conducted experimental as well as epidemiological studies have confirmed these expectations beyond doubt. Some of the noteworthy results are:
During 1995-1997 large-scale radiation exposure studies with mice at BARC, demonstrated that whole body lethal dose of gamma rays (dose 7.5 Gray or 750 rads) caused death of all mice within 20 days of irradiation. However, when mice are administered caffeine before whole body irradiation, over 70 per cent of them lived beyond 90 days.
Caffeine exerts substantial protection against tobacco-tar induced tumours in mice. A long-lived free radical, semiquinone in tobacco tar reacts with oxygen to generate ROS. In smokers who also drink coffee, the ROS is removed and therefore, tumour formation is reduced.
Data substantiating the finding that coffee reduces the risk of diabetes type 2 has been published by eminent scientists from USA, Finland, The Netherlands and Sweden. Besides caffeine, chlorogenic acid, another antioxidant (i.e. one which eliminates free radicals and ROS) in coffee plays a major role in reducing the risk to diabetes type 2.
Particularly noteworthy are the results of Harvard Medical School (USA) researchers who analyzed data involving 126,000 people for as long as 18 years concluding that coffee consumption effectively reduces risk to diabetes type 2.
Two Japanese studies suggest that coffee prevents pancreatic cancer. Caffeine also effectively reduces risk of liver and colorectal cancers.
The Robusta coffee beans have twice the amount of caffeine than Arabica which has better aroma. Coffee as health drink is far more effective than tea (green tea as well) and red wine. Further, the good old tradition of filter coffee with freshly ground coffee has much higher concentrations of many of the antioxidants than others.
Prof. M.S. Swaminathan suggests that we should develop organic coffee and coffee beans with elevated levels of caffeine, chlorogenic acid etc., for radiation workers, and others in stressful occupations.
P. C. KESAVAN (DAE- Homi Bhabha Chair & Distinguished Fellow /MSSRF, Chennai)