Immune-boosting Foods: Citrus Fruits

Grapefruit, oranges, tangerines, lemons and limes are all excellent sources of ascorbic acid, the form of vitamin C found in plants. As a component of food, this nutritional superstar has myriad immune functions, including enhancing the movement of phago¬cytes, boosting NK-cell activity and building and maintaining mucous membranes and collagen, a tissue that plays a vital role in wound healing.

Vitamin C is also required for the manufacture of hormones that help the body deal with stress and it helps convert toxins to water-soluble substances that can be excreted by the body. But it's just one of more than 100 phytochemicals that citrus fruits contain. Both oranges and grapefruit are also loaded with naringenin, which is thought to work against HIV infection and tumour formation.

The oil in citrus rinds contains Iimonene, which researchers think helps enzymes to deactivate cancer-causing substances in the body. Iimonene may also encourage tumours to shrink by slowing down the rate at which the cells divide.

The proof: Contrary to popular claims, vitamin C cannot cure the common cold or make cancer patients live longer. Even so, its importance for health can't be disputed. Many studies have found an unmistakable correlation between low levels of vitamin C in the blood and increased risk of cancer, especially cancer of the oesophagus, mouth, pancreas and stomach. Just by adding a small amount of lemon peel to their diets, participants in one US study appear to have lowered their incidence of skin cancer by as much as 34 per cent.

Put citrus fruits to work: Most animals manufacture their own vitamin C, but humans have lost their ability to do so. Since the body doesn't store the vitamin (any excess is eliminated through the urine), try to get a little bit every day. (There is no benefit in taking large doses of supplements.) To benefit from limonene, add a twist of citrus peel to your drink.