Camellia sinensis is a species of shrub in the flowering tea plant family. The leaves and buds of the plant are harvested and processed in a variety of ways, producing a range of different teas, including white tea, yellow tea, green tea, oolong tea, pu-erh (or red tea) and black tea. The different processing methods determine the oxidation level of the final tea, black tea being the most oxidised and white tea the least. Kukicha tea is also harvested from the Camellia sinensis, plant but uses the twigs and stems, not the leaves.
The top-quality leaves harvested in spring are the top two or three new leaves (known as tip buds), picked while they still have short hairs underneath. This hand-picking is repeated every one to two weeks. Older leaves have different chemical compositions and are not considered good quality.
Tea grows in tropical and subtropica regions in areas of highish rainfall with part to full sun, although hardier cultivars are grown slowly at higher and cooler latitudes and acquire more flavour. Nitrogen in the soil directly influences the quality of the tea. When regularly harvesting the leaves, the plant is trimmed to waist height for ease of picking — this has been called “industrial bonsai”. The flowers are white with yellow centres. If left undisturbed, tea shrubs will grow up to three or four metres high.
Ingredients
Fresh tea leaves contain about 4 per cent caffeine and related alkaloids such as theophylline. The caffeine acts as a natural insecticide for the plant’s protection. Tea leaves also contain the flavonoids kaempferol and tea catechins, including epigallocatechin gallate (EGCG), which has the highest antioxidant activity. L-theanine is a unique non-protein amino acid with antioxidant, anti-inflammatory and multiple health benefits.
Tea leaves also contain the inhibitory neurotransmitter GABA, which in humans has multiple functions being neuroprotective, antihypertensive, antidiabetic and an immune system stimulant.
On analysis, green and white teas have comparable levels of polyphenols and similar health-promoting properties. The therapeutic quality of the plant is also determined by how it is grown — whether wild, biodynamic or organic — the soils (high nitrogen is best) and the type and length of the fermentation process.
Therapeutic uses
Weight management
Research linking tea drinking and weight loss has shown that green tea increases thermogenesis, speeding up body metabolism, whereas oolong tea increases fat metabolism and faecal lipid excretion.
Cardiovascular
Drinking tea improves cholesterol fractions, increasing HDLs (protective cholesterol) and reducing LDLs (“bad” cholesterol), and serum cholesterol overall, thereby reducing the risk of atherosclerosis. The antioxidant properties of tea reduce high blood pressure, and research showed that drinking either green or oolong tea daily for one year significantly lowered the risk of developing hypertension in the Chinese population. Drinking more than three cups of green or black tea per day had a 21 per cent lower risk of ischaemic stroke than those drinking less than one cup a day.
Neurological
L-theanine has documented neuroprotective properties and not only regulates stressrelated disorders but also has a protective role in the progression of dementia, particularly Alzheimer’s. GABA research has shown antidepressant, anti-anxiety, stress management and neuroprotective effects and improved sleep quality.
Cancer
While green tea has undergone more extensive research, many types of tea have similar anticarcinogenic and antimutagenic properties at concentration levels equivalent to daily human consumption. Research has shown that tea can help prevent a wide variety of cancers such as prostate, breast, skin, lung and liver cancer. Green tea has demonstrated uses as an adjuvant (a substance that enhances the body’s immune response) in cancer therapy.
Dental and bone density
While research on green tea has shown it to be an effective preventative measure in dental care, black tea is a more potent inhibitor of bacterial growth. The antibacterial effect of tea on common pathogenic bacteria in the mouth is comparable with antibiotics. Green tea has been shown to be effective for reducing gum inflammation caused by dentures.
Studies have also shown that older women who drank tea regularly had higher bone mineral densities than women who did not drink tea.
Digestion
Drinking tea reduces the populations of pathogenic gut bacteria, lowers the pH of the intestines and increases levels of the beneficial bacteria lactobacillus and bifidobacterial, improving the microbiome. Pu-erh (red tea) is particularly beneficial, as the fermentation process produces effective probiotics, regulates blood sugar and contains a natural source of cholesterol-lowering compounds. Yellow tea improves constipation.
Metabolic syndrome
Metabolic syndrome is a growing public health problem, increasing the risks of diabetes and cardiovascular events. Green tea polyphenols, particularly EGCG, and pu-erh prevent the pathological conditions associated with metabolic syndrome such as obesity, insulin resistance, abnormal lipid metabolism and hypertension. An interesting study of 132 obese adults during an exercise-induced weight loss program showed that giving 625mg of tea catechins for 12 weeks induced greater loss of body weight and reduced total abdominal fat, compared with a placebo.
Consuming tea
A hot tea infusion is the ideal method of consumption, with optimal extraction of the bioactive compounds occurring at between five and 15 minutes for the leaves, but this degrades over time. The therapeutic dose of hot tea is 0.6 to 1.5 litres per day, that is two to five cups.
References are available on request.
