The review of 40 studies by researchers at the University of Nottingham, found that a diet low in vitamins A and C increases the risk of developing asthma and the increased risk was independently linked to each vitamin - people with the lowest levels of vitamin A tended to have more severe asthma than other sufferers.

The researchers analysed the data from the studies and found no link for vitamin E, but said the associations for A and C were significant, and on average, men with asthma were lacking 26% of their daily requirements of vitamin A, while women with asthma were lacking 30%.

The findings of this latest research contradict the results of a large-scale study published last year which found no link between levels of antioxidants in the diet and asthma and the Nottingham team say their study is more robust.

According to health experts a healthy diet should provide people with their daily supply of vitamins A and C - good sources of vitamin A include cheese, eggs, oily fish, milk, fortified margarine and yoghurt and good sources of vitamin C are a wide variety of fruit and vegetables, including broccoli, Brussels sprouts, sweet potatoes, oranges and kiwis.

The review included studies carried out over the last three decades, that measured dietary intake of the vitamins, or levels of vitamins in the blood - 13 of the studies related to children while the rest were in adults or were unspecified.

Lead researcher Dr. Jo Leonardi-Bee says their findings indicate that low levels of vitamin C intake and - to a lesser extent - vitamin A are consistently associated with asthma risk to a degree that, if causal, would be sufficient to be clinically relevant.

Dr. Leonardi-Bee says it is now important that larger-scale studies are carried out in order to clarify the link and to see if there was a direct cause between vitamin intake and asthma.

The review is published in the journal Thorax.

At the end of the study, the researchers found that:

In males:

Coffee: increased food intake by 21%, decreased markers of oxidative stress by 39-65%, increased markers of antioxidant enzyme protein content by 46-139%, and decreased markers of cell death by 34-36%. Caffeine: increased food intake by 22%, decreased markers of oxidative stress by 45-81%, increased markers of antioxidant enzyme protein content by 21-99%, and decreased markers of cell death by 17-22%. Chlorogenic acid: increased food intake by 12%, decreased markers of oxidative stress by 25-35%, increased markers of antioxidant enzyme proteins by 23-44%, and decreased cell death by 41-44%.

In females:

Coffee: increased food intake by 30%, decreased markers of oxidative stress by 64%, but did not increase markers of antioxidant enzymes or decrease markers of cell death. Caffeine: increased food intake by 28%, decreased motor performance by 20%, decreased markers of oxidative stress by 58%, decreased markers of antioxidant enzyme protein content by 11-48%, and increased cell death by 23-74%. Chlorogenic acid: increased markers of oxidative stress by 178%, had equivocal effects on markers of antioxidant enzyme protein content, and decreased cell death 33-39%.

Conclusion

According to Ms. Seevaratnam, "If we were to extrapolate these results to human patients with ALS, then coffee appears to be beneficial for men, both reducing oxidative stress and cell death, and increasing antioxidants. But for women, caffeine appears to be harmful. Women with the disorder may want to restrict caffeine consumption, or switch to decaffeinated products which contain the antioxidants, but with little caffeine."

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