Vitamins E plus C and interacting conutrients required for optimal health. A critical and constructive review of epidemiology and supplementation data regarding cardiovascular disease and cancer

Allyl sulfides modify cell growth

Extensive evidence points to the ability of allyl sulfides from garlic to suppress tumor proliferation both in vitro and in vivo. This antineoplastic effect is generally greater for lipid-soluble than water-soluble allyl sulfides. Both concentration and duration of exposure can increase the antiproliferative effects of lipid- and water-soluble allyl sulfides. Part of their antiproliferative effects may relate to an increase in membrane fluidity and a suppression of integrin glycoprotein IIb-IIIa mediated adhesion. Alterations in cholesterol, arachidonic acid, phospholipids and/or thiols may account for these changes in membrane function. Allyl sulfides are also recognized for their ability to suppress cellular proliferation by blocking cells in the G2/M phase and by the induction of apoptosis. This increase in the G2/M and apoptotic cell populations correlates with depressed p34cdc2 kinase activity, increased histone acetylation, increased intracellular calcium and elevated cellular peroxide production. While impressive pre-clinical data exist about the antineoplastic effects of allyl sulfur compounds, considerably more attention needs to be given to their effects in humans. The composition of the entire diet and a host of genetic/epigenetic factors will likely determine the true benefits that might arise from allyl sulfur compounds from garlic and other Allium foods.

Specific cellular responses to alpha-tocopherol

In the last 10 years precise cellular functions of alpha-tocopherol, some of which are independent of its antioxidant/radical-scavenging ability, have been revealed. Absorption of alpha-tocopherol from the gut is a selective process. Other tocopherols are not absorbed or are absorbed to a lesser extent. At the post-translational level, alpha-tocopherol inhibits protein kinase C and 5-lipoxygenase and activates protein phosphatase 2A and diacylglycerol kinase. Some genes [platelet glycoprotein IV/thrombospondin receptor/class B scavenger receptor (CD36), alpha-tocopherol transfer protein (alpha-TTP), alpha-tropomyosin, connective tissue growth factor and collagenase] are affected by alpha-tocopherol at the transcriptional level. alpha-Tocopherol also inhibits cell proliferation, platelet aggregation, monocyte adhesion and the oxygen burst in neutrophils. Other antioxidants, such as beta-tocopherol and probucol, do not mimic these effects, suggesting a nonantioxidant, alpha-tocopherol-specific molecular mechanism.

Effect of vitamin E, vitamin C, and beta-carotene on stroke risk

In a recent prospective observational study, vitamins C and E and beta-carotene did not elicit protective effects on stroke risk. Lutein, however, may elicit such protection. Nevertheless, these nutrients may be important modulators of the outcome after the occurrence of a stroke. At present, optimal control of the classic stroke risk factors in combination with increased consumption of fruits, vegetables, and antioxidant nutrients may represent the safest and most efficient strategy to control stroke risk.

Phenolic antioxidants: a rationale for design and evaluation of novel antioxidant drug for atherosclerosis

With increasing evidence that shows the involvement of active oxygen and nitrogen species in a variety of disorders, cancer, and aging, the role of antioxidant against oxidative stress has received renewed attention. In this review article, a rationale for design of lipophilic, radical-scavenging antioxidant is presented and the potency of a novel antioxidant, 2,3-dihydro-5-hydroxy-2,2-dipentyl-4, 6-di-tert-butylbenzofuran (BO-653), as an inhibitor of LDL oxidation was evaluated by considering various factors such as reactivity toward radicals, localization, and mobility in the lipoprotein, and fate of its radical. The anti-atherogenic activity of BO-653 was compared with those of alpha-tocopherol, probucol, and its metabolites. Furthermore, a novel function of phenolic antioxidants such as cell regulation and induction of phase II defense antioxidants are also discussed.

Vitamin E: non-antioxidant roles

Vitamin E was originally considered a dietary factor of animal nutrition especially important for normal reproduction. The significance of vitamin E has been subsequently proven as a radical chain breaking antioxidant that can protect the integrity of tissues and play an important role in life processes. More recently alpha-tocopherol has been found to possess functions that are independent of its antioxidant/radical scavenging ability. Absorption in the body is alpha-tocopherol selective and other tocopherols are not absorbed or are absorbed to a lesser extent. Furthermore, pro-oxidant effects have been attributed to tocopherols as well as an anti-nitrating action. Non-antioxidant and non-pro-oxidant molecular mechanisms of tocopherols have been also described that are produced by alpha-tocopherol and not by beta-tocopherol. alpha-Tocopherol specific inhibitory effects have been seen on protein kinase C, on the growth of certain cells and on the transcription of some genes (CD36, and collagenase). Activation events have been seen on the protein phosphatase PP2A and on the expression of other genes (alpha-tropomyosin and Connective Tissue Growth Factor). Non-antioxidant molecular mechanisms have been also described for gamma-tocopherol, delta-tocopherol and tocotrienols.

Selenium stimulates estradiol production in bovine granulosa cells: possible involvement of nitric oxide

Reduction in fertility is well known to be possibly related to selenium deficiencies, even if target organ for selenium action is, at present, unclear. The present study was aimed to examine whether selenium directly influences granulosa cells. Bovine granulosa cells from different size follicles were used to investigate the effect of selenium (5 ng/ml), with or without bovine follicle-stimulating hormone (bFSH) (100 ng/ml), on proliferation and steroidogenesis. In addition, we sought to determine if selenium modulates the production of nitric oxide, which is known to play an important role in ovarian activity. Our data demonstrate that selenium significantly (P < 0.001) stimulates the proliferation of the cells from small follicles; moreover, it further potentiates the stimulatory effect of the gonadotropin in the same cells. Furthermore, selenium significantly (P < 0.01) augments E2 output by cells from both kinds of follicles. bFSH increases E2 production (P < 0.01) by cells from large follicles, whereas it exerts a stimulatory (P < 0.01) effect only in the presence of selenium in the cells from the small ones. The production of nitric oxide is significantly increased (P < 0.001) by bFSH, but only in cells from small follicles. Selenium inhibits (P < 0.001) nitric oxide production in cells from both kinds of follicles and significantly decreases (P < 0.001) bFSH-induced nitric oxide production in cells from the small ones. We conclude that selenium acts on granulosa cells by modulating their proliferation and E2 synthesis; moreover, its effect could be mediated, at least in part, through an inhibition of nitric oxide.

Is ethanol an important antioxidant in alcoholic beverages associated with risk reduction of cataract and atherosclerosis?

It has been reported in the epidemiological literature that cataract, stroke, and atherosclerosis risk is reduced by 50% in people consuming one alcoholic drink per day. Peroxide has been implicated as a causative agent in cataractogenesis, and LDL oxidation appears to play a role in atherosclerosis. The antioxidant activity of alcohol was measured by: (i) use of a luminescent assay developed in our laboratory, confirmed as appropriate; (ii) electron spin resonance (ESR) spin-trapping; and (iii) copper-catalysed oxidation of LDL and VLDL from hamsters fed 6% ethanol in their drinking water. Ethanol reduced the luminescent counts/min from peroxide and superoxide. It significantly reduced the spin-trapped signal of hydroxyl radical, but not the superoxide signal. Other alcohols also showed large reductions in counts from hydrogen peroxide. Plasma from hamsters fed 6% ethanol had lower lipid peroxides and the oxidizability of LDL and VLDL was significantly reduced compared to controls. These data provide a possible explanation for the effect of beverages containing ethanol in the reduction of cataract and atherosclerosis risk observed in human population studies.

Plasma antioxidant vitamins and carotenoids in five Japanese populations with varied mortality from gastric cancer

To examine the geographic associations between plasma antioxidant levels and gastric cancer risk, we conducted an ecological study in five regions of Japan representing the threefold variation in the disease mortality within the country. Subjects were 634 men aged 40-49 years sampled randomly from the five regions with 72% response rates. Plasma concentrations of five carotenoids (beta-carotene, alpha-carotene, lycopene, lutein, and zeaxanthin), alpha-tocopherol, and ascorbic acid were measured, and the mean levels were correlated with age-adjusted mortality rates from gastric cancer. beta-Carotene and alpha-tocopherol were inversely correlated with gastric cancer rates (r = -0.31 and -0.89, respectively). alpha-Carotene and lycopene showed stronger inverse correlation than did beta-carotene (r = -0.67 and -0.56, respectively), but these relations disappeared after the exclusion of one outlying region in Okinawa with the lowest mortality. In contrast, ascorbic acid revealed a negative correlation with the exclusion of this outlier (r = -0.61). Lutein and zeaxanthin were not inversely associated with risk. The results suggest that plasma levels of beta-carotene and alpha-tocopherol, and possibly alpha-carotene, lycopene, and ascorbic acid, may partly account for the regional difference in gastric cancer mortality in Japan.

Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans

The current recommended dietary allowance (RDA) for vitamin C for adult nonsmoking men and women is 60 mg/d, which is based on a mean requirement of 46 mg/d to prevent the deficiency disease scurvy. However, recent scientific evidence indicates that an increased intake of vitamin C is associated with a reduced risk of chronic diseases such as cancer, cardiovascular disease, and cataract, probably through antioxidant mechanisms. It is likely that the amount of vitamin C required to prevent scurvy is not sufficient to optimally protect against these diseases. Because the RDA is defined as "the average daily dietary intake level that is sufficient to meet the nutrient requirement of nearly all healthy individuals in a group," it is appropriate to reevaluate the RDA for vitamin C. Therefore, we reviewed the biochemical, clinical, and epidemiologic evidence to date for a role of vitamin C in chronic disease prevention. The totality of the reviewed data suggests that an intake of 90-100 mg vitamin C/d is required for optimum reduction of chronic disease risk in nonsmoking men and women. This amount is about twice the amount on which the current RDA for vitamin C is based, suggesting a new RDA of 120 mg vitamin C/d.

Supplemental and complementary alternatives to hormone replacement therapy

Tables 1 and 2 offer a summary of information currently available on the sources, dosages, and proposed health benefits of the supplemental and complementary nutritional therapies that can be suggested as alternatives to hormone replacement therapy. These therapies have the additional benefit of being broadly available to women of all socioeconomic strata, and should be acceptable to women of various ethnicities and cultures. Adequate intakes (AI) of vitamins are recommended based on observational or experimentally determined approximations of the average nutrient intake, by a defined population or group, that appears to sustain a defined nutritional state (Food and Nutrition Boar, Institute of Medicine, 1997). Reviewing the empirical evidence concerning the use of vitamin supplements leads to the conclusion that doses higher than AI or recommended daily requirements is not warranted. For those individuals who choose to supplement, counseling should be provided to caution about tolerable upper limits, those maximum levels of nutrient intake judged unlikely to pose a risk for adverse health effects (Food and Nutrition Boar, Institute of Medicine). Supplemental and complementary therapy directed at ameliorating symptoms or reducing the risk of menopause related illness (osteoporosis and CHD) becomes a decision balance of the woman's preferences, risk and health history, and personal and financial resources. There appears to be some protection of morbidity and mortality from CHD with antioxidant dietary intake. Osteoporosis appears to be delayed with calcium supplementation. Menopausal symptoms, CHD risk, and osteoporosis risk appears to be reduced with phytoestrogen supplementation, although doses have not been established. Research concerning the safety and efficacy of these therapies continues. Findings from current clinical trials, such as the Women's Health Initiative may render these and additional alternative therapies to HRT more precise in the near future.