Changes in plasma antioxidant status following consumption of diets high or low in fruit and vegetables or following dietary supplementation with an antioxidant mixture.

The aim of the present study was to examine the effect of consumption of a high-fruit and vegetable diet, or a spray-dried extract of selected fruits and vegetables of high antioxidant content, on indices of antioxidant status of individuals consuming a background diet with minimal antioxidant intake. Plasma antioxidant concentrations were determined in twenty-five men following a 2-week depletion period during which they consumed self-selected low-antioxidant diets (less than three servings of fruit and vegetables with no tea, coffee, red wine or fruit juice). Following this period the volunteers consumed either a self-selected diet containing five to seven servings of fruit and vegetables/d, or 30 g of a spray-dried supplement designed to provide the equivalent antioxidant activity of five to seven servings of fruit and vegetables for 2 weeks in a crossover trial. Following consumption of a high-antioxidant diet for 2 weeks, plasma concentrations of ascorbic acid, alpha- and beta-carotene and lutein+zeaxanthin were all significantly increased (P < 0.05) over the depletion period. However, concentrations of lycopene, retinol and tocopherol were not affected. Consumption of the supplement also raised the concentrations of these same antioxidants in plasma. Despite the increases in the concentrations of measured antioxidant nutrients, the 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid-equivalent antioxidant capacity of plasma, as estimated by inhibition of metmyoglobin activity, was not significantly affected by any of the dietary treatments.

Protection by tea against UV-A + B-induced skin cancers in hairless mice.

Consumption of tea, especially green tea, has been shown to reduce the incidence of ultraviolet (UV)-related skin tumors in hairless mice. Because milk is added to much of the tea consumed in Western cultures, we have studied the effects of including milk in the tea consumed by hairless mice receiving simulated solar radiation. Under these conditions, mice consuming tea with 10% whole milk had 30% fewer papillomas, 50% fewer tumors, and 55% smaller lesions than mice consuming water. Mice consuming tea alone had fewer papillomas and tumors than mice consuming tea with milk; however, the difference in area affected was not statistically significant. In separate experiments, there was a significant dose response to black tea as a preventive against UV-related skin lesions, and also consumption of black tea was associated with a small but significant reduction in the incidence of papillomas in mice previously exposed to UV radiation. The results of these studies demonstrate that, in hairless mice, black tea can inhibit the formation of UV-induced skin tumors in a dose-dependent manner and, even with the addition of milk, can still inhibit the growth of UV-related skin tumors.

Protection by black tea and green tea against UVB and UVA + B induced skin cancer in hairless mice.

The effects of green and black tea consumption on the early indices of UVB and UVA + B skin damage in hairless mice have been studied in the absence of any chemical tumour initiators or promoters. Black tea consumption was associated with a reduction in the number of sunburn cells in the epidermis of mice 24 h after UVA + B irradiation, although there was no effect of green tea. Other indices of early damage such as necrotic cells or mitotic figures were not affected. Neutrophil infiltration as a measure of skin redness was slightly lowered by tea consumption in the UVB group. Consumption of either green or black tea resulted in significantly fewer skin papillomas and tumours induced by UVA + B light, however black tea provided better protection against UVB-induced tumours than green tea. This study confirms earlier reports that tea consumption can reduce the incidence of skin cancer in hairless mice, and indicates that black tea may afford more protection against simulated solar irradiation than green tea.

Folate, vitamin B12, homocysteine status and chromosome damage rate in lymphocytes of older men.

Deficient levels of folic acid and vitamin B12 are associated with elevated chromosome damage rate and high concentrations of homocysteine in the blood. We have therefore performed a study to determine the prevalence of folate deficiency, vitamin B12 deficiency and hyperhomocysteinemia in 64 healthy men aged between 50 and 70 years, and evaluate the relationship of these micronutrient levels in the blood with the micronucleus frequency in peripheral blood lymphocytes. We also performed a placebo-controlled, double-blind intervention study to determine whether supplementation of the diet with a daily dose of 0.7 mg (as a supplement in cereal) or 2.0 mg (in a tablet) over a period of 4 months resulted in a significant alteration of folate status, homocysteine status and the micronucleus index. Twenty-three per cent of the men were serum folate deficient (<6.8 nmol/l), 16% were red blood cell folate deficient (<317 nmol/l), 4.7% were vitamin B12 deficient (<150 pmol/l) and 37% has plasma homocysteine levels >10 micromol/l. In total, 56% of the men had one or more abnormal blood values for folate, vitamin B12 or homocysteine. The micronucleus index of these men (n = 34) in cytokinesis-blocked binucleated cells (19.2 +/- 1.1) was significantly elevated (P = 0.02) when compared to the micronucleus index of the rest of the men who had normal levels of folate, vitamin B12 and homocysteine (16.3 +/- 1.3, n = 30). Interestingly, the micronucleus index in men with normal folate and vitamin B12, but homocysteine levels >10 micromol/l (19.4 +/- 1.7, n = 15) was also significantly higher (P = 0.05) when compared to those with normal folate, vitamin B12 and homocysteine. This novel result was also supported by the observation that the micronucleus index and plasma homocysteine were significantly (P = 0.0086) and positively correlated (r2 = 0.172) in those subjects who were not deficient in folate or vitamin B12. The micronucleus index was not significantly correlated with folate indices, but there was a significant (P = 0.013) negative correlation with serum vitamin B12 (r2 = 0.099). Daily supplementation of the diet with 0.7 mg free folic acid in cereal for 2 months followed by 2.0 mg free folic acid via a tablet produced a 4-fold increase in plasma folate, a 2.6-fold increase in red blood cell folate and a 11% reduction in plasma homocysteine; however, these changes were not accompanied by a reduction in the micronucleus index. In conclusion, it is apparent that elevated homocysteine status, in the absence of vitamin deficiency and low, but not deficient, vitamin B12 status are important risk factors for increased chromosome damage in lymphocytes.

Cancer biomarkers in the field of tea.

Suitable intermediate end-point biomarkers are needed in order to reduce the time and expense associated with cancer chemoprevention studies. Because of the multi-step nature of cancer intermediate biomarkers reflect a continuum of events associated with different stages of disease development, and range from genetic damage linked to cancer initiation, to tumor growth and expansion during disease progression. With tea, experimental evidence points to potential protection at several stages of carcinogenesis including endogenous carcinogen formation, carcinogen activation and detoxification, DNA damage and destabilisation, cell proliferation, neoplastic growth and metastatic spread. If used effectively in tea research, biomarkers should contribute to a better understanding of the possible extent of cancer protection afforded by tea, as well as the putative mechanisms involved and the principal components of tea with prophylactic potential.

Inhibition of carcinogenesis by tea: the evidence from experimental studies.

In its various forms, tea is one of the most widely consumed beverages in the world. Elucidation of the chemical components of tea has revealed that the beverage is a rich repository of antioxidants. Among these are the polyphenolics, common to green tea, but also found in black teas together with oxidized polymers that in part account, for the darkened color. Consumption of tea on a regular basis has been associated with reduced risk of several forms of cancer in human populations, with the strongest evidence linking green tea use to reduction in cancer risk in parts of Asia. To understand how tea prevents cancer, studies in animal carcinogenesis models have been done with very encouraging results. This review examines the available data from animal studies on the effects of tea in the prevention of cancer.

Black tea, green tea, and tea polyphenols. Effects on trace element status in weanling rats.

Previous studies have shown that tea consumption can impair trace element metabolism, particularly iron status, and increase the risk of anemia in humans and animals. More recently, however, evidence has been accumulating to show that, in animals, consumption of green tea or its polyphenols is associated with a reduction of the incidence and severity of a variety of experimentally induced cancers. In this study we have monitored the growth, trace element status, including hematological parameters of weanling rats given either (1) water, (2) 1% black tea, (3) 1% green tea, or (4) 0.2% crude green tea extract as their sole drinking fluid while consuming diets containing either adequate or low amounts of iron. With the exception of manganese, none of the trace elements studied (iron, copper, zinc, and manganese) or the hematological indices measured were affected by the type of beverage supplied, even though the polyphenol extract was shown to chelate metals in vitro and all the animals fed the low iron diet were shown to be anemic. There appeared to be an effect of black and green teas on manganese balance in both the first and last weeks of the study. A lower level of brain manganese was associated with green tea consumption, and a higher level of this element in the kidneys of animals fed black tea. The results demonstrate that both black and green teas and a green tea polyphenol extract do not represent a risk to animals consuming the beverages as their sole fluid intake with respect to iron availability, although the interactions with manganese deserve further study.

Trace elements in nutrition.

Advances in trace element research over the last decade have done much to elucidate the function of these nutrients at the biochemical level. Five new trace elements have been identified and the general relevance of microelements in human nutrition has undergone reassessment. Deficiencies of iodine, iron and fluorine remain important problems and necessitate supplementation. Suboptimal nutrition in chromium, copper, selenium, zinc and possibly vanadium has been suggested, and these elements are generally acknowledged to be of concern in human nutrition. Genetic factors and other "conditioning" agents have been implicated in the aetiology of a number of trace element deficiencies in apparently well nourished communities. Tissues under anabolic stress have been recognized to be especially sensitive to trace element deficits, and the particular vulnerability of the fetus has been demonstrated on a number of occasions. In practical dietary terms, the loss of microelements during the refining and processing of food has been widely illustrated. Also, the generally lower levels of trace elements in plant material and the lower availability of minerals from these food sources has been well established. Of the newer trace element deficiencies, zinc impoverishment appears to be especially important, as a state of physiological zinc deficiency rapidly follows dietary insufficiency, and the consequences on all growing tissues are particularly serious. In general, recent developments suggest that marginal deficiencies of microelements are more widespread in human nutrition than was previously appreciated. Greater attention to trace element status seems to be indicated in circumstances in which physical condition and vigour are unaccountably poor and especially in situations accompanied by active anabolism.

A site of action for zinc in neoplastic tissue.

The effect of dietary zinc levels on DNA synthesis in transplanted hepatomas induced by 3'-methyl-4-dimethyl-amino-azobenzene was investigated. DNA synthesis was found to be reduced (P less than 0,01) in rats maintained on diets low in zinc (0,5 mug/g) and high in zinc (less than 500 mug/g) when compared with the control animals given 60 mug zinc/g ration. Subsequently, the effect of dietary zinc intakes on the activity of 2 zinc-dependent enzymes associated with DNA synthesis--thymidine kinase and DNA polymerase--was studied. Both thymidine kinase and DNA polymerase activity was significantly reduced in animals receiving the zinc-deficient (0,5 mug/g) and zinc-supplemented (less than 500 mug/g) diets when compared with the control animals (60 mug/g). The data indicated that the DNA synthesis was the primary locus associated with zinc deficiency and zinc supplementation in proliferating tumour tissue, and that the site of action of zinc in this process was probably thymidine kinase, since there was considerable doubt concerning the role of DNA polymerase in DNA synthesis.