Introduction
Tea, in general, is considered the most consumed drink in the world, next to the water. The green tea variant is one of many beverages, commonly drunk hot, that is a staple of breakfast and break menus. Consciously or not, people are habituated to green tea, other tea varieties, and coffee for the caffeine content that re-energizes them for some time after consuming the beverage.
When a coffee lover is unable to get his or her regular cup, blood flow to the brain spikes. This is the result of vasodilation of the blood vessels in the brain. The abnormal blood flow is felt as a headache. This headache, accompanied by fatigue and grumpiness, continues until the person finally gets some coffee. In the absence of coffee, the afflicted individual must identify another source of caffeine. Green tea is one such replacement source of caffeine, just as effective that does not engender any adverse reactions.
A Background on Green Tea
Green tea originated from different regions of China, Japan, and other Asian countries. Because of this, there are different types of green tea. These varieties differ considerably because of the different growing conditions, harvesting, processing, and most especially because of their country of origin. However, all the different types of green tea are brewed from one common plant, Camellia sinensis.
In the past century, modern medicine has achieved, through intensive effort and well-funded research, many discoveries. Besides such mainstream breakthroughs as the germ theory and the development of computer-assisted tomography (CAT) whole-body scanning, increased awareness of the value of orientalist and herbalist remedies paved the way for re-discovery and validation of herbal remedies and dietary supplements that were popular since ancient times in East Asia. Some of these remedies include ginger, ginseng, wild yam, and of course, green tea. Over the past decades, green tea has been the subject of much research and comment in the professional medical literature. There have been suggestions that green tea lowers the chances of contracting certain types of cancer, as well as heart ailments. Green tea is also popular among those individuals who seek to lose weight because the beverage seems to be effective in helping the overweight manage his or her weight.
The Active Ingredients and Vital Components of Green Tea
Green tea is known to contain important vitamins and minerals such as ascorbic acid (vitamin c), zinc, selenium, chromium, and manganese, which are all life-sustaining. Ascorbic acid is essential for collagen synthesis, prevention of scurvy, enhanced absorption of iron in the gastrointestinal tract, prevention of certain cancers, and regulation of the blood’s oxygen-carrying capacity. Zinc is a mineral known to reduce the duration of symptoms of common colds in adults, enhance wound healing, cure acne when applied topically with the antibiotic erythromycin, and alleviate rheumatoid arthritis symptoms. Selenium is a proven antioxidant that helps with the pain and stiffness attending arthritis, as well as preventing certain types of cancers, such as lung, colon, rectal, and prostate cancer. Magnesium serves as a direct muscle depressant; deficiency of this mineral leads to increased neuromuscular irritability, severe vomiting, muscle tremor, convulsive seizures, depression, and delirium. Lastly, the chromium present in green tea serves as a complementary therapy for type 2 diabetics who are chromium deficient, as well as for individuals with elevated cholesterol and triglycerides. Aside from the above vitamins and minerals, green tea also contains beneficial tocopherols and carotenoids.
Benefits of the Beverage
Green tea is not fermented, unlike the other tea variants. It also contains more catechins than black tea. Green tea has antibacterial as well as antiviral activity. The beverage is also effective in increasing bone mineral density and boasts anti-fibrotic properties as well as neuroprotective power. Green tea promotes oral health as well as other physiological functions, such as being an anti-hypertensive agent. This makes green tea not only one of the most popular drinks but also one of the healthiest drinks in the world. (Cabrera, 2006)
As previously mentioned, green tea contains catechins, which is a healthy type of polyphenol. A study on the efficacy of green tea extract, which was rich in catechin polyphenols and caffeine, showed that green tea has thermogenic properties. Also, it was proven to promote fat oxidation, over and above the action of its caffeine content. Green tea extract was also proven to have a role in controlling body composition by sympathetic activation of thermogenesis and fat oxidation (Duloo et al., 1999).
Green tea is known to have a beneficial effect by way of normalizing blood pressure, total cholesterol levels, body weight, and fat. A study done on healthy volunteers suggested that short-term consumption of commercially-available green tea can reduce diastolic and systolic blood pressure, fasting cholesterol, body weight, and percent body fat, which reduces the risk of having cardiovascular diseases (Dujaili, 2009). The same study also shows that reductions may be more evident in overweight and obese individuals, most especially those people who have high risks of having cardiovascular diseases. Thus, green tea is highly recommended most especially to those who are obese and overweight because the beverage stands a good chance of helping them manage weight, blood pressure, cholesterol levels, and overall health better.
A Japanese team investigated the correlation between green tea consumption and mortality due to all causes, with particular emphasis on cardiovascular diseases, and cancer. This study showed that regular intake of green tea is linked to a reduction of mortality with regards to all causes, most especially cardiovascular diseases. However, consumption of green tea appeared to not affect the life expectancy of cancer patients (Kuriyama, 2006).
Green tea also improves vascular function and reduces LDL oxidability (Tinahones, 2008). A study on 14 healthy female volunteers (not experiencing any medical treatments), were asked to drink green tea extract. There was a significant increase in the average diameter of the brachial artery after the treatment, (after the post-compression hyperemia phase. This seems to have been explained by a simultaneously occurring and significant reduction(37.4 %) in the concentration of oxidized Low-Density Lipoprotein(LDL) upon consumption of green tea extract. After the treatment, there was a significant decrease in the levels of oxidized LDL IgM antibodies. This study proves that drinking green tea for at least five weeks alters the vascular function and decreases the serum oxidizability of healthy women.
Aside from catechin, one of the most important components of green tea is Epigallocatechin gallate(EGCG). It is speculated that EGCG embodies the anti-cancer effect of green tea and this component has therefore been the focus of early research. In different epidemiological studies, researchers have proven that consumption of 5-6 cups of green tea a day provides metabolic health and cardiovascular benefits. As it happens, this is the same amount of green tea, which contains 200-300 mg of EGCG, in total, confirmed for efficacy in maintaining cardiovascular and metabolic health (Wolfram, 2007).
Disease Prevention vis-à-vis Coffee
We draw a comparison with coffee since it is the next most popular hot beverage worldwide after tea as a group. A study was done on subjects who drank four 8-ounce cups of coffee daily (an average of 400 milligrams of caffeine) for a whole week found a 35 percent decrease in insulin sensitivity, which increases the risk of diabetes. On the other hand, it was demonstrated that green tea improves insulin sensitivity and oxidative stress in laboratory animals (rats) with induced insulin resistance (Hininger-Favier, 2009). There are three signposts of insulin resistance: hyperglycemia, hypertriglyceridemia, and hyperinsulinemia. Investigators observed that rats who were given tea solids (as a dietary supplement) displayed a decrease in blood sugar, insulin, and triglycerides. The results were consistent with the insulin-incentive effect of tea in humans. This is one more experimental finding bolstering a protective effect against insulin resistance. In the same study, there was a pronounced decrease in sulfhydryl (SH) group oxidation, plasma lipid peroxidation, as well as DNA oxidative damage in rats with increased tea consumption. This indicates that green tea decreases oxidative stress. Both sets of findings suggest that green tea is beneficial for patients with decreased insulin sensitivity and those with elevated oxidative stresses such as those with type 2 diabetes, non-insulin-dependent diabetics, and people with metabolic syndrome. If patients with diminished insulin sensitivity or pronounced oxidative stress were coffee drinkers, to begin with, these findings indicate they should switch to green tea.
A study was done on Epigallocatechin-3-Gallate (EGCG), a key polyphenol present in green tea, showed that EGCG induces heme oxygenase in rat neurons and acts as an effective neuroprotective agent or defense against oxidative stress (Romeo, 2009). Six hours of incubation of cultured rat neurons with 25 to 100 micrograms of EGCG was enough to stimulate elevated expression of HO-1 mRNA and protein. Also, there was activation of Nrf2 and the transcription factor NF-E2-related factor-2. When the incubation test was extended to 12 hours employing 50 micrograms of EGCG, improved cellular resistance to glucose oxidase-mediated oxidative damage was observed. This effect is considered cytoprotective and was caused by zinc protoporphyrin IX, which inhibits heme-oxygenase activity. By activating the transcription factor Nrf2, the EGCG present in green tea appears able to protect against cell death caused by oxidative stress.
Lastly, EGCG helps protect brain tissue from cell death in mice with induced Alzheimer’s and Parkinson’s diseases. EGCG was also able to ‘rescue’ the neurons which were already damaged, a phenomenon known as neurorestorative (Mandell, 2007).
According to the US Food and Drug Administration, coffee contains from 130 to 330 milligrams of caffeine per 16 oz cup, the range owing to bean variety, brand/grind mixture, and the locality where grown. On the other hand, green tea only has 30 mg of caffeine per 16 oz cup, about 5 to 10 times less than coffee. Why is this disparity important?
Caffeine is considered a CNS (central nervous system) stimulant and is in fact, legally classed as a psychoactive substance. As a stimulant, caffeine wards off stupor and drowsiness, and restores alertness, although these effects are transient. Aside from this, caffeine is not meant to replace sleep but simply reduces the sensation of being tired. Caffeine is a diuretic and excessive “doses” may cause dehydration.
When taken in large amounts over prolonged periods, caffeine leads to “Caffeinism”, which is characterized by dependency, nervousness, anxiety, muscle twitching, irritability, respiratory alkalosis, insomnia, heart palpitations, peptic ulcer, and headaches.
There is also a condition called caffeine jitters. This happens when the person experiences an acute overdose of caffeine (>300mg: varies based on caffeine tolerance and body weight) which leads to overstimulation of the central nervous system, a condition medically known as caffeine intoxication. Symptoms consist of excitement, flushing of the face, nervousness, insomnia, increased renal excretion (urination), gastrointestinal disturbance, tachycardia or irregular heartbeat, and psychomotor agitation. In severe cases of overdose, caffeine intoxication may lead to mania, lapses in judgment, depression, disorientation, delusions, hallucinations, disinhibition, psychosis, and breakdown of muscle tissue(skeletal muscle cells), medically known as rhabdomyolysis.
Extreme overdose of caffeine, measured in rats as 192 mg. per kilogram (lethal dose 50) causes death. In humans, lethal dose 50 (level 4 toxicity or death for 50% of humans) is equivalent to 150 to 200 mg per kg. of bodyweight, which is equivalent to 30 to 80 cups of coffee (BW=50 kg) taken in a specific period based on the half-life of caffeine in the body of the subject.
Another factor that underlies the perils of continuing to drink coffee is that this beverage has a fat-like substance known as cafestol. Cafestol increases the cholesterol level and is not reduced when coffee is decaffeinated.
People love drinking coffee for its high caffeine content because it increases alertness and reduces sluggishness, whether early in the morning or late in the evening. However, elevated levels of caffeine produce appalling effects, which may lead to life-threatening disorders. Therefore, it is more advisable to drink green tea; a moderate amount of caffeine is sufficient to obtain the stimulant action without having all the unhealthy side effects that coffee incurs. Aside from this, green tea has a lot of positive effects, from lowering blood cholesterol levels and triglyceride levels to protecting the body from oxidative stress, as well as containing a great many beneficial and essential nutrients, vitamins, and minerals.
References
Cabrera C., Atacho, R., & Gimenez, R., (2006). Beneficial effects of green tea – A review. Journal of the American College of Nutrition, 25, (2) 79-99.
Dujaili, E.A., Bradley, J.P., & Almoosawi, S., (2009). Effects of green tea consumption on blood pressure, total cholesterol, body weight and fat in healthy volunteers. European Congress of Endocrinology, 20: 470.
Dulloo, A. G., et al. (1999). Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans. American Journal of Clinical Nutrition, 70 (6) 1040-5.
Hininger-Favier, I., et al. (2009). Green tea extract decreases oxidative stress and improves insulin sensitivity in an animal model of insulin resistance: The fructose-fed rat. Journal of American College of Nutrition, 28 (4) 492S-499S.
Kuriyama, S., et al. (2006). Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan. Journal of the American Medical Association, 296 (10) 1255-1265.
Romeo, L., et al. (2009). The major green tea polyphenol, epigallocatechin-3-gallate, induces heme oxygenase in rat neurons and acts as an effective neuroprotective agent against oxidative stress. Journal of the American Medical Association, 28, (4) 492S-499S.
Tinahones, F.J., et al. (2008). Green tea reduces LDL oxidability and improves vascular function. Journal of American College of Nutrition, 27 (2) 209-213.
Wolfram, S., (2007) Effects of green tea and EGCG on cardiovascular and metabolic health. Journal of the American College of Nutrition, 26, (4) 373S-388S.