The deleterious long-term health effects of smoking are though to be caused by increased levels of oxidative stress. It is thought that cigarette smoking increases tissue free radical activity that gradually depletes cellular antioxidant defences, and over time, the plasma membrane, nucleic acids and proteins become damaged by oxidative stress. Free radical concentrations in inhaled cigarettes are known to be high and free radicals are associated with smoking related diseases such as emphysema, chemical carcinogenesis and atherosclerosis. The free radical theory of disease therefore has some merit when explaining the deleterious effects of cigarette smoking to long-term health. Because fruits and vegetables contain high concentrations of antioxidants, they may offer benefits to smokers against the long-term damage associated with oxidative stress. Nutritional researchers are interested in evaluating the effects of fruit and vegetable consumption in smokers by measuring changes in biomarkers of free radical damage.
For example, researchers1 have used a randomised, double-blind placebo controlled study to investigate the effects of powdered supplements of fruit and vegetable on the oxidative stress of 101 healthy smokers. Subjects were assigned to receive either a powdered supplement without berry extract, a powdered supplement with berry extract, or a placebo, for 3 months. Oxidised low density lipoprotein (LDL) and total malonaldehyde (free plus bound malonaldehyde) were used as markers of systemic oxidative stress and lipid peroxidation, respectively. Following 3 months of supplementation, both treatment groups had significant decreases in oxidised LDL and free malonaldehyde (a measure of recent lipid peroxidation) levels, and an increase in bound malonaldehyde (a measure of older lipid peroxidation). In addition, significant reductions in the ratio of the oxidative species to the total antioxidant barrier (oxidative index) were reported in the treatment groups when compared to the placebo.
Supplementing smokers with fruit and vegetable supplements may therefore be effective at decreasing some of the measures of oxidative stress in smokers. The fruit and vegetable supplement in this study provided roughly 234mg vitamin C, 7.5mg β-carotene, 32mg vitamin E and 420 µg folic acid. The supplement with berry extract provided roughly 200mg vitamin C, 7.5mg β-carotene, 60mg vitamin E and 600 µg folic acid. Not surprisingly, before supplementation (at baseline), the smokers had an imbalance in oxidative stress in favour of pro-oxidation. This was demonstrated by a higher oxidative index in the smokers compared to non-smoking controls. While free malonaldehyde levels fell, they were still elevated compared to non-smokers following supplementation. The increase in bound malonaldehyde is significant because binding gradually converts free malonaldehyde to bound malonaldehyde. The ratio of free to bound malonaldehyde is therefore a temporal measure of lipid peroxidation, in this case showing a reduction.
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