Antioxidant vitamins are not “just antioxidants”: Not necessarily harmful when targeted to the right population (original) (raw)
Related papers
Recent evidence does not support a causational relationship between antioxidant supplements and reduced risk of coronary heart disease and other age-related pathologies. Advances in the understanding of the complex interactions between reactive oxygen species (ROS) and antioxidants “in vivo” and of the role of mitochondria in the adaptive response to oxidative stress suggest that physiological production of ROS in mitochondria is one of the most essential contributions to the maintenance of health and longevity. Through mechanisms linked to the concept of mitochondrial hormesis, a moderate transient increase in ROS formation increases the body's antioxidant defences by activating enzymes sensitive to oxidative stress and redox-sensitive transcription factors, while high doses of antioxidants may inhibit this adaptive response.
Antioxidants and health: A report on the recent RSH conference held on 23rd October, 1996
The Journal of the Royal Society for the Promotion of Health, 1996
Antioxidants are man-made or natural substances that may prevent or delay some types of cell damage. Diets high in vegetables and fruits, which are good sources of antioxidants, have been found to be healthy; however, research has not shown antioxidant supplements to be beneficial in preventing diseases. Examples of antioxidants include vitamins C and E, selenium, and carotenoids, such as betacarotene, lycopene, lutein, and zeaxanthin. This fact sheet provides basic information about antioxidants, summarizes what the science says about antioxidants and health, and suggests sources for additional information. Key Points-Vegetables and fruits are rich sources of antioxidants. There is good evidence that eating a diet that includes plenty of vegetables and fruits is healthy, and official U.S. Government policy urges people to eat more of these foods. Research has shown that people who eat more vegetables and fruits have lower risks of several diseases; however, it is not clear whether these results are related to the amount of antioxidants in vegetables and fruits, to other components of these foods, to other factors in people's diets, or to other lifestyle choices.
Oxidative stress is a significant factor in the development of chronic diseases. An improved antioxidant potential in the body can reduce oxidative stress and prevent or improve disease conditions. Some food nutrients, especially vitamin C, E, and carotenoids are well-known antioxidants; however, other vitamins such as Vitamin K, Vitamin D, Niacin, Pyridoxine and Riboflavin that may have antioxidant potential are usually not put into consideration. This review entails studies that have investigated the antioxidant properties of other vitamins with the known antioxidants inclusive and their effect in reducing oxidative stress. The reviewed studies suggest that other vitamins possess antioxidant nature, and they can improve oxidative stress, ranging from lipid peroxidation, protein carbonylation, and reduction of advanced glycated end-products. Therefore, proper attention should be given to these neglected vitamins in research activities on oxidative stress, nutrition and the management of diseases related to oxidative stress.
Antioxidant supplementation for health -a boon or a bane?
Antioxidants (vitamins E and C, β-carotene, superoxide dismutase [SOD], catalase etc.) are the substances that protect cells from the damage caused by free radicals, formed as a result of oxidative stress. Free radicals (O2−, H2O2, OH−, ROO− etc.) are generated during the cellular metabolism and also due to environmental effects (cigarette smoke, ionizing radiations). Excessive production of free radicals has been implicated in the causation and progression of several diseases, e.g., atherosclerosis, cancer, rheumatoid arthritis, diabetes, and cataract. The general belief is that since free radicals are bad for health, antioxidants are good. This led to an indiscriminate use and supplementation of antioxidants, which is currently a controversial issue. This review gives an updated information on the effects of supplementation of antioxidants (vitamins E and C, β-carotene, SOD, catalase etc.). While some studies suggest that antioxidants are benefi cial and protective, other interven...
Reconvene and reconnect the antioxidant hypothesis in human health and disease
Indian Journal of Clinical Biochemistry, 2010
The antioxidants are essential molecules in human system but are not miracle molecules. They are neither performance enhancers nor can prevent or cure diseases when taken in excess. Their supplemental value is debateable. In fact, many high quality clinical trials on antioxidant supplement have shown no effect or adverse outcomes ranging from morbidity to all cause mortality. Several Chochrane Meta-analysis and Markov Model techniques, which are presently best available statistical models to derive conclusive answers for comparing large number of trials, support these claims. Nevertheless none of these statistical techniques are flawless. Hence, more efforts are needed to develop perfect statistical model to analyze the pooled data and further double blind, placebo controlled interventional clinical trials, which are gold standard, should be implicitly conducted to get explicit answers. Superoxide dismutase (SOD), glutathione peroxidase and catalase are termed as primary antioxidants as these scavenge superoxide anion and hydrogen peroxide. All these three enzymes are inducible enzymes, thereby inherently meaning that body increases or decreases their activity as per requirement. Hence there is no need to attempt to manipulate their activity nor have such efforts been clinically useful. SOD administration has been tried in some conditions especially in cancer and myocardial infarction but has largely failed, probably because SOD is a large molecule and can not cross cell membrane. The dietary antioxidants, including nutrient antioxidants are chain breaking antioxidants and in tandem with enzyme antioxidants temper the reactive oxygen species (ROS) and reactive nitrogen species (RNS) within physiological limits. Since body is able to regulate its own requirements of enzyme antioxidants, the diet must provide adequate quantity of non-enzymic antioxidants to meet the normal requirements and provide protection in exigent condition. So far, there is no evidence that human tissues ever experience the torrent of reactive species and that in chronic conditions with mildly enhanced generation of reactive species, the body can meet them squarely if antioxidants defense system in tissues is biochemically optimized. We are not yet certain about optimal levels of antioxidants in tissues. Two ways have been used to assess them: first by dietary intake and second by measuring plasma levels. Lately determination of plasma/serum level of antioxidants is considered better index for diagnostic and prognostic purposes. The recommended levels for vitamin A, E and C and beta carotene are 2.2-2.8 lmol/l; 27.5-30 lmol/l; 40-50 lmol/l and 0.4-0.5 lmol/l, respectively. The requirement and recommended blood levels of other dietary antioxidants are not established. The resolved issues are (1) essential to scavenge excess of radical species (2) participants in redox homeostasis (3) selective antioxidants activity against radical species (4) there is no universal antioxidant and 5) therapeutic value in case of deficiency. The overarching issues are (1) therapeutic value as adjuvant therapy in management of diseases (2) supplemental value in developing population (3) selective interactivity of antioxidant in different tissues and on different substrates (4) quantitative contribution in redox balance (5) mechanisms of adverse action on excess supplementation (6) advantages and disadvantages of prooxidant behavior of antioxidants (7) behavior in cohorts with polymorphic differences (8) interaction and intervention in radiotherapy, diabetes and diabetic complications and cardiovascular diseases (9) preventive behavior in neurological disorders (10) benefits of non-nutrient dietary antioxidants (11) markers to assess optimized antioxidants status (12) assessment of benefits of supplementation in alcoholics and heavy smokers. The unresolved and intriguing issues are (1) many compounds such as vitamin A and many others possessing both antioxidant and non-antioxidant properties contribute to both the activities in vivo or exclusively only to non-antioxidant activity and (2) since human tissues do not experience the surge of FR, whether there is any need to develop stronger synthetic antioxidants. Theoretically such antioxidants may do more harm than good.
Clinical pharmacology and therapeutic use of antioxidant vitamins
Fundamental & Clinical Pharmacology, 2007
The clinical use of antioxidants has gained considerable interest during the last decade. It was suggested from epidemiological studies that diets high in fruits and vegetables might help decrease the risk of cardiovascular disease. Therefore, supplements of vitamins C and E were applied through protocols aimed to prevent diseases such as atherosclerosis, preeclampsia or hypertension, thought to be mediated by oxidative stress. Despite the biological properties of these vitamins could account for an effective protection, as shown by several clinical and experimental studies, their efficacy remains controversial in the light of some recent clinical trials and meta-analyses. However, the methodology of these studies, criteria for selection of patients, the uncertain extent of progression of the disease when initiating supplementation, the lack of mechanistic studies containing basic scientific aspects, such as the bioavailability, pharmacokinetic properties, and the nature of the antioxidant sources of vitamins, could account for the inconsistency of the various clinical trials and meta-analyses assessing the efficacy of these vitamins to prevent human diseases. This review presents a survey of the clinical use of antioxidant vitamins E and C, proposing study models based on the biological effects of these compounds likely to counteract the pathophysiological mechanisms able to explain the structural and functional organ damage.
Ten misconceptions about antioxidants
Oxidative damage is a common cellular event involved in numerous diseases and drug toxicities. Antioxidants prevent or delay oxidative damage, and therefore there has been extensive research into the discovery of natural and newly designed antioxidants. Initial excitement regarding the potential health benefits of antioxidants has diminished. Currently, it is even claimed that antioxidants increase mortality. The antioxidant pendulum appears to swing from healthy to toxic and from general panacea to insignificant ingredient. Owing to the polarity of views towards antioxidants, nutritional recommendation ranges from advice to increase antioxidant status in plasma to the notion that it is a useless measurement. Such views, lacking sufficient scientific support, lead to misconceptions, which in our opinion hinder the rational use of food supplements and impedes the design and development of new antioxidant drugs. As a result, good opportunities might easily be missed.
Weighing the benefits of dietary antioxidant supplements
Journal of Food Technology, 2018
Evidence is building that consumption of large doses of dietary antioxidant supplements may not always render beneficial health effects and some may even have a negative effect. There are few reasons why this happens. Firstly, the role of free radicals causing various chronic diseases is not yet fully clear. There are also some beneficial actions conferred by free radicals in human physiology. Secondly, antioxidant capacity in the body coupled with immune system may resist the action of dietary antioxidants. Lastly, the dosage of antioxidants taken may be inappropriate. Some misconceptions about free radicals and antioxidants are discussed. In fact, low to moderate level of prooxidants might sometimes be better in stimulating the endogenous antioxidant enzyme defence system for overall human health. Consumption of natural foods rich in antioxidants such as fruits, vegetables, nuts, and grains, among others, may provide a better option for health promotion instead of taking high dosages of dietary antioxidant supplements.
An overview on antioxidant supplements. The current situation from a scientific point of view
Agro Food Industry Hi Tech, 2012
Accumulating evidence demonstrates that damage to cellular components from reactive oxygen species (ROS) plays an integral role in the age-related deterioration of biochemical and physiologic processes and in the incidence of age-related disease. In the late 1980s, many in vitro studies and early observational studies have suggested a role of antioxidants in the prevention of the ROS-induced damage involved in the etiopathogenesis of coronary artery disease. This led to a substantial increase in the use of antioxidant supplements for the prevention of c a r d i o v a s c u l a r d i s e a s e s a n d o t h e r a g e-r e l a t e d pathologies. Unexpectedly, recent more rigorous scientific evaluation did not support a causational relationship between antioxidant supplements and lowering the risk of c o r o n a r y a r t e r y d i s e a s e a n d o t h e r a g e-r e l a t e d pathologies (1). Moreover, supplementation with antioxidants has been linked to increased incidence of a number of diseases with adverse effects on human longevity (2, 3). Recent advances in the comprehension of the complex interaction between ROS and antioxidants in vivo and the role of mitochondria in the adaptive response to oxidative stress can help in understanding these seemingly contradictory data. Oxidative stress-i.e., an excessive production of ROS outstripping endogenous antioxidant defence capacity-is implicated in oxidative damage to nucleic acids, proteins, carbohydrates, and lipids. It is well known that mitochondria are the primary site for ROS generation as a by-product of aerobic metabolism, and that the accumulation of mitochondrial oxidative damage over time diminishes t h e c e l l u l a r e f f i c i e n c y i n e n e r g y production. ROS-induced damage is complex and frequently irreversible, and it further impairs mitochondrial function, rendering them prone to further ROS generation. This feedforward relationship between mitochondrial ROS generation and damage was hypothesized to be responsible for oxidative stress and accelerated ageing (4).