Antioxidant impact of juice not due to vitamin C
Experts believe that heart disease and cancer have their origins in long-term damage to the body’s cells caused by free radicals. Free radicals are highly reactive molecules created during normal metabolism or via exposure to pollutants in the environment e.g. cigarette smoke. Normally, the body is able to protect itself from free radical damage with antioxidant nutrients in the blood. However, the stress of daily life combined with poor diets often leaves individuals with a deficient antioxidant defence. This increases the importance of dietary sources of antioxidants.
One major source of antioxidants in the diet is fruit juice, particularly orange juice which is rich in vitamin C. Vitamin C is used widely in food manufacturing to prevent spoilage (oxidation). In the same way, vitamin C is believed to protect human cells from oxidation by free radicals. However, a number of clinical trials, involving vitamin C supplementation, produced disappointing results. This has left researchers wondering whether the antioxidant capacity of orange juice might be due to other nutrients, not vitamin C.
To test this, seven healthy subjects were asked to consume a different test drinks on three separate occasions. The three drinks were pure blood orange juice, a sweet drink with added vitamin C, and a sweet drink with no vitamin C. All drinks contained the same amount of sugars. Subjects were given the drinks in a random order, and two weeks elapsed between each type of drink to allow blood levels to return to normal.
On each occasion after consuming 300ml of the test drink, subjects were asked to give blood samples to estimate whether the vitamin C in the drinks was being absorbed. This was confirmed when blood levels of vitamin C were seen to rise after the orange juice and ‘vitamin C’ drink, but not after consumption of the ‘vitamin-free’ drink.
The researchers then tested the subjects’ blood to discover whether the drinks had affected resistance to free radical damage on blood DNA (genetic material from blood cells). The results showed that DNA damage was 18% lower when subjects had drunk the pure blood orange juice. The protective effect persisted for 24 hours. No such effect was seen with either the ‘vitamin C’ or ‘vitamin-free’ test drinks. This was despite the fact that the ‘vitamin C’ drink contained as much vitamin C as the pure orange juice (150mg/glass).
This study showed that drinking 300ml of pure blood orange juice was enough to protect the body’s cells from free radical damage for 24 hours. However, the protective effect was not due to the vitamin C, suggesting that other important nutrients are at work in orange juice. It also suggests that vitamin C pills would not influence our risk of chronic diseases.
For more information, see Guarnieri S et al (2007). Orange juice vs vitamin C: effect on hydrogen peroxide-induced DNA damage in mononuclear blood cells
British Journal of Nutrition, vol 97, pp 639-643.