Latin name: Theaceae
Common names: Tea
Allergens for serum IgE testing are extracted from ordinary fermented Black tea from Ceylon or a blend of several Black teas derived from various locales, including India, Sri Lanka, Kenya, Malawi and China. Oolong tea is not included.
A food, which may result in allergy symptoms in sensitised individuals.
The only beverage more frequently consumed worldwide than Tea is water. The Tea plant, Camellia sinensis, is a member of the Theaceae family and is a tropical and subtropical evergreen shrub or tree that can grow to 10 metres but is usually pruned to under 2 metres for cultivation. Tea has been cultivated for more than 5,000 years, since the reign of the Chinese emperor Shen Nung. It was introduced to Britain in the 17th century, but the custom of afternoon Tea did not start until the early 19th century.
The leaves of this plant are dark green, alternate and oval, with serrated edges, and the blossoms are white and fragrant and sometimes form clusters. From the leaves are produced all of the types of the beverage most commonly known as Tea (as opposed to specialised herbal and fruit “teas” made from steeping other plants). The hundreds of varieties of Tea plants, each with its distinctive leaves, grow from the same species but in many different environments in about 30 countries. However, all Tea plants are essentially the same, particularly in that the dry leaves contain 3-6% caffeine, which is responsible for the stimulating effect of the beverage, (1) and an epigallocatechin gallate concentration of less than or equal to 10% (2). The largest differences between the end products are due to the methods of preparation.
These methods yield 3 major types of Tea. Black tea, the kind that is by far the most popular worldwide and in the West, comes from leaves that have been fermented before being heated and dried. In this way, oxidation of green leaf polyphenols is promoted so that most of these substances are oxidized. (The polyphenols found in Tea are more commonly known as flavonols or catechins and comprise 30-40 percent of the extractable solids of dried Green tea leaves. The polyphenol unique to Tea is theogallin [3-galloylquinic acid].) Such leaves produce a dark reddish-brown brew. Black teas are graded according to the size of the leaf; for example, “orange pekoe” describes leaves that are smaller than the medium-size, coarser pekoe leaves. Although Black tea flavours vary, most are stronger than those of Green or Oolong teas. Among the better known Black teas are Darjeeling, English breakfast and Lapsang Souchong. Earl Grey tea is a Black tea treated with oil of bergamot, which gives it its characteristic taste.
Green tea is prepared in such a way – basically from fresh leaves – as to preclude the oxidation of green leaf polyphenols. Green tea composition is similar to that of the fresh leaf except for a few enzymatically catalysed changes brought on by plucking alone, and some new volatile substances produced during the drying stage. Among the most famous Green teas are Longjing (Dragon Well), Yinzhen (Silver Needle), and Yunwu (Cloud and Mist). Twenty percent of worldwide Tea consumption is of Green tea, but the product’s popularity is spreading beyond its base in China and Japan.
Oolong tea is a partially oxidised product. It combines the freshness of Green tea and the fragrance of Black tea and is increasingly popular, though it still commands only 2% of the market. The bush grows on cliffs, so the difficulty of harvesting makes the final product costly.
Brick tea and Scented tea are types known principally in the Orient. Scented tea is a mixture, through an elaborate process, of Green tea with petals of Rose, jasmine, orchid and Plum. Brick tea is black or Green tea pressed into blocks. There are other kinds of Tea, such as White tea, that are also largely unfamiliar to the West.
Tea is available commercially mainly in Tea bags and as loose fragmented or whole leaves. In East Asia, Tea tends to be served plain, but from India west the traditional additives are many, the most popular being spices, sugar, milk, cream, lemon and other fruit. Iced teas are made hot but served chilled, sometimes with added flavours. Ice teas are also sold as instant mixes.
The Tea ceremony in Japan and afternoon Tea in Great Britain are long-entrenched customs. More importantly, Tea is consumed in enormous amounts in many industrialised countries, which have mainly sedentary workforces and easy availability of Tea and Tea-making facilities in workplaces. Most importantly of all as far as allergy is concerned, the Tea industry is a large, hands-on and labour-intensive one in several of the world’s most populous countries, including India and China; the results in occupational allergy are striking.
The medicinal properties of Tea have been widely explored. The main catechins in Green tea are epicatechin, epicatechin-3-gallate, epigallocatechin, and epigallocatechin-3-gallate (EGCg), with the latter being the highest in concentration. Green tea polyphenols have demonstrated significant antioxidant, anticarcinogenic, anti-inflammatory, thermogenic, probiotic, and antimicrobial properties in numerous human, animal, and in vitro studies (3-4). Tea is a rich source of fluoride but reduces the absorption of iron from food.
No allergens from this plant have yet been characterised.
Epigallocatechin gallate (EGCg), a component of Green tea leaves, is reported to be a causative agent in occupational Tea-induced asthma from inhalation of Green tea dust (5).
An extensive cross-reactivity among the different individual species of the genus could be expected but has not been documented in the literature.
Tea may uncommonly induce symptoms of food allergy in sensitised individuals, but is more commonly associated with occupational asthma resulting from the inhalation of Tea dust (2, 5-7). Chronic Tea dust exposure has been reported to increase the prevalence of respiratory symptoms and can result in a significant degree of small airway obstruction in Tea workers (8).
The first reported case of occupational asthma to Tea in a Tea maker was reported over 3 decades ago (9). Subsequently, a number of studies reported occupational asthma as a result of Tea dust among workers involved in packaging Tea bags or during the blending of Tea, resulting in acute and chronic symptoms (10-12). Of 125 Tea blenders with an average service of 22.9 years in the industry, 46 workers (36%) had respiratory illness, 31 had chronic bronchitis (24.8%), 8 had asthma (6.4%), and 7 had active or inactive pulmonary tuberculosis (5.6%). The prevalence of chronic bronchitis and asthma was more than that expected in the general population (13).
Studies have better defined the effects of Tea dust on Tea workers. A study described 3 patients who worked in Green tea factories and developed asthmatic and nasal symptoms after exposure to Green tea dust. Catechins, the major components of Green tea leaves, were evaluated, and epigallocatechin gallate (EGCg; MW: 458 daltons), a major catechin, was isolated and further evaluated in these 3 patients. All 3 patients exhibited an immediate skin and bronchial response to EGCg. A Prausnitz-Kustner skin test with EGCg was also positive (6).
The same researchers described occupational Green tea-induced asthma and rhinitis as a result of the inhalation of Tea dust in 11 Green tea factory workers. Epigallocatechin gallate (EGCg) was reported to be the causative agent. Five of the 11 also developed food allergy to Green tea; i.e., their asthma worsened after drinking Tea (14). The food allergy symptoms described as a result of ingesting Green tea included cough, dyspnoea, and in a severe case, loss of consciousness, all occurring soon after the ingestion of Oolong and Black teas as well as Green tea; and after ingestion of cakes or noodles containing Green tea powder. Strict elimination of all Teas resulted in the disappearance of symptoms (2).
In a study of 63 Green tea workers, females were more likely to report shortness of breath than males, and the prevalence of nasal allergies overall was 11% (15).
Not all studies have had comparable findings. In 83% of workers at a Tea-packing plant who were exposed to Tea dust and participated in a study, the prevalence of asthma, wheezing, hay fever and atopy were found to be similar to that in the general population. Work-related nasal symptoms were most commonly reported by blenders and operators. Nonetheless, specific IgE to Black or Chamomile tea was found in 5.6% of these employees; but there was little evidence of specific allergic sensitisation to the Tea varieties tested. The authors concluded that the work-related respiratory and nasal symptoms probably represented non-specific irritation (16).
Not all Tea-like beverages are made from Camellia sinensis, and many “teas” are derived from other plants. In an early study of 100 female “tea” workers, chronic respiratory symptoms were most frequently reported by workers processing dog rose tea, followed by sage and Georgian tea (17). A subsequent study by the same author examined the immunological status and respiratory function of 26 females employed in processing different types of “tea.” Skin tests demonstrated the highest percentage of positive reactions to sage (45%), gruzyan (40%), mentha (35%), and dog rose (10%) teas. Among 17 skin-tested control workers, 23% had positive skin reactions to sage, 19% to gruzyan, 20% to mentha and 11% to dog rose and Indian teas. Serum levels of total IgE were increased in 27% of the workers and in 7% of the control subjects. Prevalence of almost all chronic respiratory symptoms was higher in “tea” workers with positive skin tests than in those with negative skin tests to the allergens. Workers with positive skin tests to the allergens had lung functions suggesting an obstructive effect, mostly in the smaller airways. Bronchoprovocation testing with different “tea” allergens provoked acute reductions of ventilatory capacity in 4 out of 6 subjects tested (18).
Present in a herbal product, Tea may increase the risk of bleeding or potentiate the effects of warfarin therapy (19).
Repeated muscle cramps and distal paraesthesias in all limbs, and a feeling of pressure in the eyes, associated with blurred vision, particularly in darkness, were reported in a 44-year-old male drinking more than 4 L of Tea per day (20).
Tea contains caffeine, which may result in adverse symptoms in certain individuals who either drink excess amounts of caffeine or are intolerant to caffeine (21).
Symptoms may include irritability, tachycardia, chronic headaches, urticaria and anaphylaxis (22-25).
- Ramarethinam S, Rajalakshmi N. Caffeine in tea plants [Camellia sinensis (L) O. Kuntze]: in situ lowering by Bacillus licheniformis (Weigmann) Chester. Indian J Exp Biol 2004;42(6):575-80.
- Shirai T, Hayakawa H, Akiyama J, Iwata M, Chida K, Nakamura H, Taniguchi M, Reshad K. Food allergy to green tea. [Letter] J Allergy Clin Immunol 2003;112(4):805-6
- No authors listed. Green tea. Altern Med Rev 2000;5(4):372-5.
- McKenna DJ, Hughes K, Jones K. Green tea monograph. Altern Ther Health Med 2000;6(3):61-8, 70-2,
- Shirai T, Sato A, Chida K, Hayakawa H, Akiyama J, Iwata M, Taniguchi M, Reshad K, Hara Y. Epigallocatechin gallate-induced histamine release in patients with green tea-induced asthma. Ann Allergy Asthma Immunol 1997;79(1):65-9.
- Shirai T, Sato A, Hara Y. Epigallocatechin gallate. The major causative agent of green tea-induced asthma. Chest 1994;106(6):1801-5.
- Zuskin E, Kanceljak B, Skuric Z, Tonkovic-Lojovic M, Mataija M, Turcic N. Respiratory and immunologic changes in tea workers. [Croatian] Arh Hig Rada Toksikol 1988;39(3):297-305
- Jayawardana PL, Udupihille M. Ventilatory function of factory workers exposed to tea dust. Occup Med (Oxf) 1997;47(2):105-9
- Uragoda CG. Tea maker's asthma. Br J Ind Med 1970;27(2):181-2
- Cartier A, Malo JL. Occupational asthma due to tea dust. Thorax 1990;45(3):203-6
- Roberts JA, Thomson NC. Tea-dust induced asthma. Eur Respir J 1988;1(8):769-70
- Lewis J, Morgan WK. Tea asthma: response to specific and non-specific challenges. Br J Ind Med 1989;46(5):350-1
- Uragoda CG. Respiratory disease in tea workers in Sri Lanka. Thorax 1980;35(2):114-7
- Shirai T, Reshad K, Yoshitomi A, Chida K, Nakamura H, Taniguchi M. Green tea-induced asthma: relationship between immunological reactivity, specific and non-specific bronchial responsiveness. Clin Exp Allergy 2003;33(9):1252-5
- Mirbod SM, Fujita S, Miyashita K, Inaba R, Iwata H. Some aspects of occupational safety and health in green tea workers. Ind Health 1995;33(3):101-17.
- Abramson MJ, Sim MR, Fritschi L, Vincent T, Benke G, Rolland JM. Respiratory disorders and allergies in tea packers. Occup Med (Lond) 2001;51(4):259-65
- Zuskin E, Skuric Z. Respiratory function in tea workers. Br J Industrial Med 1984;41:88-93
- Zuskin E, Kanceljak B, Skuric Z, Ivankovic D. Immunological and respiratory changes in tea workers. Int Arch Occup Environ Health 1985;56(1):57-65.
- Heck AM, DeWitt BA, Lukes AL. Potential interactions between alternative therapies and warfarin. Am J Health Syst Pharm 2000;57(13):1221-7
- Finsterer J. Earl Grey tea intoxication. Lancet 2002:359(9316):1484
- Nawrot P, Jordan S, Eastwood J, Rotstein J, Hugenholtz A, Feeley M. Effects of caffeine on human health. Food Addit Contam 2003;20(1):1-30
- Caballero T, Garcia-Ara C, Pascual C, Diaz-Pena JM, Ojeda A Urticaria induced by caffeine. J Investig Allergol Clin Immunol 1993;3(3):160-2
- Infante S, Baeza ML, Calvo M, De Barrio M, Rubio M, Herrero T. Anaphylaxis due to caffeine. Allergy 2003;58(7):681-2
- Quirce Gancedo S, Freire P, Fernandez Rivas M, Davila I, Losada E. Urticaria from caffeine. J Allergy Clin Immunol 1991;88(4):680-1
- Schonewille WJ. Chronic daily headaches caused by too much caffeine. [Dutch] Ned Tijdschr Geneeskd 2002 5;146(40)