Approximately 200 studies that examined the relationship between fruit and vegetable intake and cancers of the lung, colon, breast, cervix, esophagus, oral cavity, stomach, bladder, pancreas, and ovary are reviewed. A statistically significant protective effect of fruit and vegetable consumption was found in 128 of 156 dietary studies in which results were expressed in terms of relative risk. For most cancer sites, persons with low fruit and vegetable intake (at least the lower one-fourth of the population) experience about twice the risk of cancer compared with those with high intake, even after control for potentially confounding factors. For lung cancer, significant protection was found in 24 of 25 studies after control for smoking in most instances. Fruits, in particular, were significantly protective in cancers of the esophagus, oral cavity, and larynx, for which 28 of 29 studies were significant. Strong evidence of a protective effect of fruit and vegetable consumption was seen in cancers of the pancreas and stomach (26 of 30 studies), as well as in colorectal and bladder cancers (23 of 38 studies). For cancers of the cervix, ovary, and endometrium, a significant protective effect was shown in 11 of 13 studies, and for breast cancer a protective effect was found to be strong and consistent in a meta analysis. It would appear that major public health benefits could be achieved by substantially increasing consumption of these foods.

Fruit, vegetables, and cancer prevention: A review of the epidemiological evidence

The total antioxidant activity of 12 fruits and 5 commercial fruit juices was measured in this study using automated oxygen radical absorbance capacity (ORAC) assay. On the basis of the wet weight of the fruits (edible portion), strawberry had the highest ORAC activity (micromoles of Trolox equivalents per gram) followed by plum, orange, red grape, kiwi fruit, pink grapefruit, white grape, banana, apple, tomato, pear, and honeydew melon. On the basis of the dry weight of the fruits, strawberry again had the highest ORAC activity followed by plum, orange, pink grapefruit, tomato, kiwi fruit, red grape, white grape, apple, honeydew melon, pear, and banana. Most of the antioxidant capacity of these fruits was from the juice fractions. The contribution of the fruit pulp fraction (extracted with acetone) to the total ORAC activity of a fruit was usually less than 10%. Among the commercial fruit juices, grape juice had the highest ORAC activity followed by grapefruit juice, tomato juice, orange juice, and apple juice.

Total Antioxidant Capacity of Fruits

Free radicals and other reactive oxygen species (ROS) are constantly formed in the human body. Free-radical mechanisms have been implicated in the pathology of several human diseases, including cancer, atherosclerosis, malaria, and rheumatoid arthritis and neurodegenerative diseases. For example, the superoxide radical (O2·−) and hydrogen peroxide (H2O2) are known to be generated in the brain and nervous system in vivo, and several areas of the human brain are rich in iron, which appears to be easily mobilizable in a form that can stimulate free-radical reactions. Antioxidant defenses to remove O2·− and H2O2 exist. Superoxide dismutases (SOD) remove O2·− by greatly accelerating its conversion to H2O2. Catalases in peroxisomes convert H2O2 into water and O2 and help to dispose of H2O2 generated by the action of the oxidase enzymes that are located in these organelles. Other important H2O2-removing enzymes in human cells are the glutathione peroxidases. When produced in excess, ROS can cause tissue injury. However, tissue injury can itself cause ROS generation (e.g., by causing activation of phagocytes or releasing transition metal ions from damaged cells), which may (or may not, depending on the situation) contribute to a worsening of the injury. Assessment of oxidative damage to biomolecules by means of emerging technologies based on products of oxidative damage to DNA (e.g., 8-hydroxydeoxyguanosine), lipids (e.g., isoprostanes), and proteins (altered amino acids) would not only advance our understanding of the underlying mechanisms but also facilitate supplementation and intervention studies designed and conducted to test antioxidant efficacy in human health and disease.

/pdf/free-radicals-oxidative-stress-and-antioxidants-in-human-3vj10xn342.pdf

Free radicals, oxidative stress, and antioxidants in human health and disease

https://zenodo.org/record/1258621/files/article.pdf

Oxygen-radical absorbance capacity assay for antioxidants

Previously, some fruits were shown to contain high antioxidant activities. In this paper, we report the antioxidant activities of 22 common vegetables, one green tea, and one black tea measured using the automated oxygen radical absorbance capacity assay with three different reactive species:  a peroxyl radical generator, a hydroxyl radical generator, and Cu2+, a transition metal. Based on the fresh weight of the vegetable, garlic had the highest antioxidant activity (μmol of Trolox equiv/g) against peroxyl radicals (19.4) followed by kale (17.7), spinach (12.6), Brussels sprouts, alfalfa sprouts, broccoli flowers, beets, red bell pepper, onion, corn, eggplant (9.8−3.9), cauliflower, potato, sweet potato, cabbage, leaf lettuce, string bean, carrot, yellow squash, iceberg lettuce, celery, and cucumber (3.8−0.5); kale had the highest antioxidant activity against hydroxyl radicals followed by Brussels sprouts, alfalfa sprouts, beets, spinach, broccoli flowers, and the others. The green and black teas had muc...

Antioxidant Capacity of Tea and Common Vegetables

Previous cross-cultural comparisons of the mortality from ischemic heart disease in European communities with associated plasma levels of essential antioxidants have revealed strong inverse correlations for vitamin E and relatively weak correlations for other antioxidants Similarly, in a case-control study in Edinburgh low plasma levels of vitamin E were significantly associated with an increased risk of previously undiagnosed angina pectoris whereas low levels of other essential antioxidants lacked statistical significance The current Basel Prospective Study is particularly well suited to elucidate the impact of antioxidants other than vitamin E In this population (which was recently evaluated regarding cancer mortality) the plasma levels of vitamins E and A are exceptionally high and above the presumed threshold level of risk for ischemic heart disease The present 12-year follow-up of cardiovascular mortality in this study reveals a significantly increased relative risk of ischemic heart disease and stroke at initially low plasma levels of carotene (< 023 mumol/l) and/or vitamin C (< 227 mumol/l), independently of vitamin E and of the classical cardiovascular risk factors Low levels of both carotene and vitamin C increase the risk further, in the case of stroke even with significance for overmultiplicative interaction In conclusion, in cardiovascular disease independent inverse correlations may exist for every major essential antioxidant although the latter can also interact synergistically Therefore future intervention trials of antioxidants in the prevention of ischemic heart disease should primarily test the simultaneous optimization of the status of all principal essential antioxidants

Poor plasma status of carotene and vitamin C is associated with higher mortality from ischemic heart disease and stroke: Basel Prospective Study.

Plasma antioxidant vitamins A, C, and E and carotene were measured in a group of 2,974 men participating in the third examination of the prospective Basel Study in 1971-1973. In 1985, the vital status and mortality of all participants were assessed. A total of 204 men had died from cancer, including 68 with bronchus cancer and 37 with gastrointestinal cancer (20 with stomach cancer and 17 with large bowel cancer excluding cancer of the rectum). Overall mortality from cancer was associated with low mean plasma levels of carotene adjusted for cholesterol (p less than 0.01) and of vitamin C (p less than 0.01). Bronchus and stomach cancers were associated with a low mean plasma carotene level (p less than 0.01). Subjects with subsequent stomach cancer also had lower mean vitamin C and lipid-adjusted vitamin A levels than did survivors (p less than 0.05). After calculation of the relative risk using the Cox model with exclusion of mortality during the first 2 years of follow-up, low plasma carotene (below quartile 1) was associated with a significantly increased risk for bronchus cancer (relative risk (RR) = 1.8, p less than 0.05), low plasma levels of carotene and vitamin A with all cancers (RR = 2.47, p less than 0.01), and low plasma retinol in older subjects (greater than age 60 years) with lung cancer (RR = 2.17, p less than 0.05). Low levels of vitamin C increased the risk of stomach cancer (RR = 2.38) and gastrointestinal cancer (RR = 2.46) in older subjects, but only significantly with the inclusion of the first 2 years. The authors conclude that low plasma levels of antioxidant vitamins are associated with an increased risk of subsequent cancer mortality. This effect was stronger in men above age 60 years at blood sampling, and the effect seems to be site-specific.

Plasma Antioxidant Vitamins and Subsequent Cancer Mortality in the 12-Year Follow-up of the Prospective Basel Study

Migration studies and secular trends suggest that human cancer may be dependent to a large extent on exogenous influences.' Dietary factors may act on initiation or promotion of tumors or exert a protective effect at various levels of carcinogenesis? This may involve a ubiquitous mechanism like scavenging free radicals or the interference with specific processes such as nitrosamine formation or cellular proliferation and differentiati~n.~ Aggressive oxygen species such as the superoxide anion, the hydroxyl radical, and singlet oxygen have been implicated in cancerogenesis. Essential antioxidants, for example, beta-carotene and the vitamins A, C, and E are part of the body's multilevel defence system against oxygen radicals. These compounds may be considered as natural inhibitors4 affecting cancer initiation or promotion. Vitamin E protects fatty acids of cell membranes against peroxidation and may thus inhibit the formation of tumor-promoting compounds? The action of vitamin E probably depends on the presence of ascorbic acid. Thus vitamins may act synergistically. Different cancer incidences in populations imply possibilities of cancer prevention. Hence, hypotheses derived from metabolic and molecular studies have to be verified in epidemiological studies and finally proven by successful intervention.

M. Eichholzer

Papers

Poor plasma status of carotene and vitamin C is associated with higher mortality from ischemic heart disease and stroke: Basel Prospective Study.

Plasma Antioxidant Vitamins and Subsequent Cancer Mortality in the 12-Year Follow-up of the Prospective Basel Study

Cancer mortality and vitamin E status.