Antioxidants observational studies

See also Antioxidants Observational Studies Intervention Studies. Ascorbic Acid Physiology, Dietary Sources and Requirements. Carotenoids Chemistry, Sources and Physiology Epidemiology of Health Effects. Copper. Folic Acid. Riboflavin. Selenium. Vitamin E Physiology and Health Effects. Zinc Physiology. 

The roles of these modifiable risks have thus become more important, and other risks interventions, such as dietary antioxidants (32) and physical activity (33), have also been highlighted. In addition, observational studies have implicated hyperhomocysteinemia as a powerful risk... 

An observational study, part of a population-based case-control study of dietary antioxidants and asthma, has shown an association between the regular use of paracetamol and the incidence of asthma and rhinitis in adults (10). After controlling for potential confounding factors the OR for asthma in daily users, compared with never users, was 2.38 (Cl = 1.22,4.64). Not unexpectedly, there was also an association in users and non-users of aspirin, strongest when cases with more severe disease were compared with controls. This adverse effect of paracetamol may be due to depletion of the antioxidant glutathione in the lungs. However, further studies are needed before paracetamol can be blamed for an increase in the prevalence and severity of asthma. 

In the last decade, an expectation of coronary benefit had been a major reason for postmenopausal hormone use because observational studies indicated that women who use hormone therapy have a 35% to 50% lower risk of coronary heart disease than nonusers. In addition, previous studies have shown that estrogen exerts protective effects on the cardiovascular system, including lipid-lowering,antioxidant, and vasodilating effects. Nevertheless, recent randomized clinical trials have provided no evidence of cardiovascular disease protection and even some evidence of harm with hormone therapy " (Table 80-8). 

In summary, trials of antioxidant supplementation of smokers and nonsmokers with vitamin C, a-tocopherol, or p-carotene did not generally find significant decreases in biomarkers of oxidative DNA damage, in contrast to observational studies, which suggest an inverse association between dietary antioxidant intake and oxidative DNA damage. 

Diet and Antioxidant Defense Intervention Studies Observational Studies... 

The poor results with the two phenols were unexpected in view of their effectiveness as antioxidants in emulsions. R, Stadnick and A, Govil investigated the effect of a-tocopherol in a system identical to that used in the present study except for the absence of the oil phase (14), They found that after incubation for 90 hours, the recovery of nitrite in the presence of a-tocopherol was half that observed in its absence. 

Despite their potential health-promoting effects as dietary antioxidants, the fate of betalains in humans has been poorly studied. Betalain bioavailability was first demonstrated in humans by the appearance of betacyanins in urines after ingestion of beetroot extract" and red beet juice," indicating that these compounds are indeed absorbed. Although intact betacyanins (betanin and isobetaiun) appeared rapidly in human urine with a maximum excretion rate observed within 2.5 to 8 hr," betacy-anin recoveries in human urine were usually low (< 1% of the dose) over 24 hr postdose, suggesting that either the bioavailabifity of betacyaiuns from red beetroot is low or that renal clearance is a minor excretion route for these compounds. 

Results obtained in in vivo and ex vivo experiments are of various types. Some studies have found positive effects of the consumption of carotenoids or foods containing carotenoids on the markers of in vivo oxidative stress, even in smokers. Other studies demonstrated no effects of carotenoid ingestion on oxidative stress biomarkers of lipid peroxidation. " It should be noted that for studies using food, the activity observed may also be partly due to other antioxidant molecules in the food (phenols, antioxidant vitamins) or to the combination of actions of all the antioxidants in the food. 

Esterbauer et al. (1991) have demonstrated that /3-carotene becomes an effective antioxidant after the depletion of vitamin E. Our studies of LDL isolated from matched rheumatoid serum and synovial fluid demonstrate a depletion of /8-carotene (Section 2.2.2.2). Oncley et al. (1952) stated that the progressive changes in the absorption spectra of LDL were correlated with the autooxidation of constituent fatty acids, the auto-oxidation being the most likely cause of carotenoid degradation. The observation that /3-carotene levels in synovial fluid LDL are lower than those of matched plasma LDL (Section 2.2.2) is interesting in that /3-carotene functions as the most effective antioxidant under conditions of low fOi (Burton and Traber, 1990). As discussed above (Section 2.1.3), the rheumatoid joint is both hypoxic and acidotic. We have also found that the concentration of vitamin E is markedly diminished in synovial fluid from inflamed joints when compared to matched plasma samples (Fairburn etal., 1992). This difference could not be accounted for by the lower concentrations of lipids and lipoproteins within synovial fluid. The low levels of both vitamin E and /3-carotene in rheumatoid synovial fluid are consistent with the consumption of lipid-soluble antioxidants within the arthritic joint due to their role in terminating the process of lipid peroxidation (Fairburn et al., 1992). 

Epidemiological studies in Europe reveal an inverse relationship between plasma vitamin E levels and the incidence of ischaemic heart disease (Gey and Puska 1989), and the risk of angina pectoris appears to increase with low plasma levels of vitamins E, A and C (Rie-mersma et al., 1991). These interesting observations require further population-based controlled intervention trials with specific supplements of antioxidant vitamins (Gey etal., 1991). 

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