Antioxidants and Disease Outcome Interventional Trials

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There are many small short-term interventional trials showing a highly variable effect of antioxidant supplementation on markers of oxidation, glucose disposal and vascular reactivity. Differences in study design, the type and preparation of antioxidants used and lack of information as to the oxida-tive state of the population studied may explain some of the discrepancies in the outcome of these studies. However, the true clinical role of antioxidant therapy has to be evaluated in large randomized, double-blind and placebo-controlled studies.

Some of the larger interventional studies that have been published are summarized in table 2. The outcomes of these studies are not always consistent. The Cambridge Heart Antioxidant Study (CHAOS) [34] and Antioxidant Supplementation in Atherosclerosis Prevention (ASAP) study [35] found a beneficial effect of vitamin E intake. The randomization of subjects in the CHAOS trial was fraught with problems, the number of events was small and the follow-up interval was short. The study population in the ASAP trial may have been deficient in vitamin E at baseline, and therefore the results of this study cannot be generalized to people with adequate vitamin E stores. In this study, the progression of carotid atherosclerosis was reduced only in the group of men who were smokers and consumed both vitamin E (136IU) and vitamin C (250 mg) daily [35]. It is likely that the smokers are under greater oxidative stress hence they benefited the most from the antioxidants. The validity of the randomization and consumption of the vitamin supplements in each group was confirmed by showing that the plasma levels of a-tocopherol and ascorbate were appropriately increased by approximately 50-90% in those subjects who were randomized to receive the supplements [35].

Another trial showing the potential benefits of antioxidants was the Nutrition intervention trials in Linxian, China [36]. In this trial 29,548 Chinese participants were assigned to one of following combinations of supplements: (a) retinol 5,000 IU + zinc 22.5 mg; (b) riboflavin 3.2 mg + niacin 40 mg; (c) ascorbic acid 120 mg + molybdenum 30 ^g, or (d) p-carotene 15 mg + selenium

Table 2. Large clinical trials conducted to delineate the role of antioxidant vitamins in preventing disease states

Study de Gaetano et al. [43]a

Primary Prevention Project

Yusuf et al. [37]a HOPE trial

Salonen et al. [35] ASAP

Lee et al. [44] Women's Health Study

GISSI trial [38]a GISSI-P

Hennekens et al. [45]

Study population

4,495 Italians at risk of CVD

2,545 women 6,996 men 55 years or older at high risk of CVD

520 men and postmenopausal women aged 45-69 years

39,876 women aged 45 years or older

11,324 Italian patients surviving recent (<3 months) MI

22,071 male physicians

Study design and follow-up

Randomized, placebo-controlled 3.6-year follow-up

Double-blinded, randomized trial with a two by two factorial design

Randomized, double-blind, placebo-controlled, 3-year follow-up

Randomized, double-blind, placebo-controlled. Treated for 2.1 years and followed for 2 additional years

Randomized, placebo-controlled, with a 3.5-year follow-up

Randomized, double-blind,

Antioxidants assessed

Vitamin E 300mg/day

Vitamin E 400 IU/day for a mean of 4.5 years

Subjects were given one of the following treatments

(a) 91 mg d-a-tocopherol

(b) 250 mg slow-release vitamin C

(c) combination of above, or

(d) placebo

P-carotene 50 mg, vitamin E 600 IU, and aspirin 100 mg given on alternate days either alone or in various combinations of the three

Patients were assigned to receive n-3 polyunsaturated fatty acid 1 g daily, vitamin E 300 mg daily, both or none P-carotene 50-mg tablets given on alternate days

Results of study

Vitamin E showed no benefit

Vitamin E showed no benefit

The progression of atherosclerosis was reduced in male participants who were smokers and were assigned to the combined treatment of vitamin E and C

There was no harm or benefit demonstrated in the subjects receiving the p-carotene

Vitamin E conferred no significant benefit p-carotene had no adverse or beneficial effect even after

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