Free radicals are molecules with unpaired electrons, and this makes them unstable and reactive. Free radicals react with stable molecules and in the process electrons are transferred from the stable molecule to the radical. This stabilises the radical but in the process causes the donor molecule to become radicalised itself. This process continues in a chain reaction until some molecule intercedes in order to donate electrons to the radical to stabilise its structure. An antioxidants is a chemical that can donate an electron to a radical, but which can then dissipate the unbalanced change of the unpaired electron amongst its structure, thus maintaining its stability. This means they are able to quench free radical chain reactions without becoming overly reactive themselves. Radicalised antioxidants are recycled by other antioxidants and eventually stabilised through cellular reductive processes. Some antioxidants such as glutathione are endogenously produced while other antioxidants are exogenous plants chemicals.
Vitamin C is an exogenous antioxidant that is essential to human health. Vitamin C functions in synergy with glutathione and exogenous antioxidants such as vitamin E and carotenoids to maintain the reducing power within cells. In this regard vitamin C protects cells from oxidative stress caused by free radicals. The high levels of oxidative stress that are associated with free radicals can deplete the body of antioxidants. When tissue antioxidant defences become depleted disease can ensue. The free radical theory of disease suggests that it is uncontrolled oxidative stress caused by free radicals that are a primary driver of the cellular dysfunction that leads to diseases such as cardiovascular disease and cancer. It is known that lifestyle habits can have a strong influence on the generation of free radicals and therefore the risk of disease. Smoking has been shown for example to increase the free radical concentrations in tissues and is therefore associated with oxidative stress and disease, particularly cancer and cardiovascular disease.
However, the free radical theory of disease suggests that for a lifestyle factor to be problematic there must first be a depletion of antioxidants in tissues. Once antioxidant defences are depleted uncontrolled oxidative stress can lead to the damage of cellular components including the genetic material. Smoking has been shown to deplete the body of antioxidants which may be the reason for its association with disease. Smokers may have a higher requirement for dietary antioxidants that non-smokers. For example, in one study1 the requirement for vitamin C was estimated in smokers compared to non-smokers. The metabolic turnover of vitamin C was measured using radiolabeled vitamin C at intakes of between 30 to 180 mg per day. Subjects smoking 20 cigarettes a day had a significantly higher turnover of vitamin C compared to non-smokers. The researchers estimated that the smokers required 140 mg per day of vitamin C in order to satisfy a steady state of vitamin C in their plasma compared to 100 mg per day for non-smokers.
Dr Robert Barrington’s Nutritional Recommendation: The recommended intake of vitamin C is 60 mg per day for humans, and this is the amount that will prevent the majority of individuals getting scurvy. As can be seen in the results from this study, this amount is too low to maintain a steady state of plasma vitamin C in even non-smoking humans. Although, it is likely that even 100 mg is not enough to maintain optimal vitamin C status. Evidence suggest that fruit rich diets supply around 600 mg of vitamin C per day. However, plasma saturation is not reached until around 2500 mg per day. Smokers may be able to protect themselves from many of the detrimental effects of smoking with higher intakes of vitamin C. However, other antioxidants should be considered just as important. In this respect polyphenols, terpenes, stilbenes, carotenoids and chalcones may be beneficial to the health of smokers, as in combination these antioxidants may confer additional benefits when compared to single isolated compounds.
RdB
