Q. What function does vitamin C play in the body?
A Vitamin C has a variety of roles, all indispensable to good health. It is needed for the body to make the protein of connective tissue, or collagen, which is found throughout the body and helps to maintain the structure of tissues, including skin, muscles, gums, blood vessel s and bone. In the classic deficiency disease, scurvy, which has been recognized for many centuries, a lack of vitamin C leads to the breaking open of small blood vessels, the reddening and bleeding of skin and gums, loose teeth, general weakness and, eventually, death.
Like vitamin E and beta-carotene, vitamin C acts as an antioxidant This means it helps to neutralize potentially harmful reactions in the body - reactions which can lead to cell damage associated with cancer, heart disease and an array of other health problems.
Q But what does this mean in terms of health or disease?
A. Lots of claims have been made regarding vitamin C, and studies are showing that, at least in some cases, these claims are valid. Vitamin C has been found to help prevent - not cure - cancer, to boost immunity against colds and other infections, to combat heart disease and to speed wound healing and help to prevent bedsores. It also appears to help overcome some types of male infertility and, in smokers, may even help to prevent sperm abnormalities which can lead to birth defects. It seems to counteract asthma, protect the lungs .against smoke and various pollutants, reduce some kinds of allergic response, and help to prevent cataracts.
Q. Right, let's take these one at a time. How is vitamin C thought to help prevent cancer?
A. Studies done in the last decade or so show that vitamin C offers strong protection from cancer. Of 46 population studies looking at vitamin C intake, 33 found a significantly reduced risk of cancer in people with the highest intake. People taking most vitamin C are about half as likely to get cancer as people taking least. High amounts of vitamin C were generally 150 mg or more a day; low amounts, 60 mg or less. This difference is equivalent to about 4 fl. oz (300 ml) of orange juice.
The protective effect seems to be strongest for cancers of the oesophagus, larynx, mouth and pancreas. Vitamin C also seems to provide some protection against most of the other common types of cancer.
Q. What's the protective mechanism at work here?
A. Researchers say that vitamin C may shield against cancer (I) by helping to protect a cell's genetic material from oxidative damage which can lead to cancerous changes; (2) by neutralizing chemical compounds such as nitrosamines - preservatives (often found in cold meats and bacon) which increase your chances of gastrointestinal cancer; and (3) by improving your immune system's ability to track down and destroy precancerous cells.
Q. And what's the story on colds? Does vitamin C really knock them out?
A. Some people swear it works, and, in fact, an analysis of a dozen studies of vitamin Cs effect on colds shows a 37 per cent average reduction in the duration of colds treated with vitamin C. in several studies the number of days sick was cut from about 7 to 5. Most of the studies also report a reduction in the severity of symptoms, such as sneezing, coughing and sniffling. To do this job properly, however, you need more vitamin C than you will get from your diet.
You really need at least 1,000
Q. How does vitamin C work against colds?
A. This is not quite clear, but the effect is almost certainly an antioxidant one. The vitamin may shield both immune cells and surrounding tissue from the oxidative reactions that occur when immune cells fight viruses. Vitamin C lowers blood levels of histamine, a biochemical (released by immune cells) which can trigger tissue inflammation and a runny nose.
Q. What about heart disease? How is vitamin C supposed to prevent that?
A. Vitamin C helps to prevent the apparent first step in the development of heart disease - the oxidation of artery-clogging LDL cholesterol. Oxidation is a chemical process in which a molecule combines with oxygen and loses electrons. Once LDL cholesterol is oxidized, it quickly turns into hard, artery-narrowing aeposos, producing, in short, the arterial disease of atherosclerosis which is the outstanding cause of coronary thrombosis.
In a study by researchers at the UCLA School of Public Health, high vitamin C intake was more strongly associated with reduced risk of heart disease than either low cholesterol levels or a low-fat diet. The study found that men with the highest vitamin C intake - an average of 140 mg a day of vitamin C from foods and pills - had a death rate 42 per cent lower than predicted.
Q. How is vitamin C supposed to prevent bedsores?
A. It's well documented that vitamin C deficiencies lead to slower wound healing because of defective collagen -the cause of scurvy. And in a recent British study of people confined to bed because of hip fractures, low levels of vitamin C increased their risk of developing bedsores.
Q. And male infertility problems? What is vitamin C supposed to do for these?
A. Researchers have found that a common form of male infertility, caused by sperm cells clumping together, can be reversed with supplementation of about I g (1,000 mg) daily of vitamin C Researchers at the University of California at Berkeley have also found that low intakes of vitamin C increase genetic damage in spertn cells, which could lead to birth defects. When test subjects increased their intakes of vitamin C to 60 mg or even higher, genetic damage dropped.
Q. How is vitamin C supposed to protect against asthma or air pollution?
A. Vitamin C acts as an antioxidant in the lungs and, so, may help to protect the lungs from the damaging effects of cigarette smoke and air pollutants. In studies, exposure to cigarette smoke or air pollutants such as ozone depleted vitamin C in the lungs.
Because of its antihistamine and anti-inflammatory actions, vitamin C may also make lungs less reactive to spasm-causing irritants and, so, help reduce asthma and allergy attacks. One study showed that a 500-mg dose of vitamin C taken an hour and a half before vigorous exercise lessened bronchial spasms in some people with asthma.
Q. And what about cataracts? Can vitamin C prevent them?
A Cataracts occur when proteins in the eye's lens oxidize, turning an opaque, milky white. In animal studies, vitamin C has been found to protect eye lenses against ultraviolet damage, reducing the incidence of cataracts. And in a recent study of 77 men and women with cataracts and 35 without, an important difference seemed to be how much fresh yellow, green and red fruits and vegetables they ate. Eating fewer than 3!/2 helpings a day increased their risk of cataracts nearly sixfold.
Q What does vitamin C have to do with the eye?
A Vitamin C is highly concentrated in the lens of the eye which may contain 60 times the amount of vitamin C found in the blood, it's possible that vitamin C helps to protect the clear lens tissue from oxidative damage resulting from exposure to sunlight Vitamin C may also protect enzymes within the lens which remove oxidation-damaged proteins, helping the eye heal itself.
Q How much vitamin C are people supposed to get?
A The R.NI for vitamin C is 60 mg a day. An American recommendation of 100 mg a day for smokers, the first RN1 to establish smokers as a special-needs group, was established in 1989, based on research showing that cigarette smoking depletes vitamin C in the body, Other studies have shown that amounts above the RNI are necessary to provide optimum vitamin C protection against the ceil damage caused by free radicals. In fact, many experts would make two points about this. To that smokers should take more vitamin C is to encourage them to go on smoking, and this is certainly the worst thing anyone concerned about health could do. Taking vitamin C is no substitute for stopping smoking. Secondly, 100 mg of vitamin C a day is almost certainly not enough to ensure .an adequate antioxidant effect. Most people concerned to achieve this take 1,000 mg a day.
QUICK-REFERENCE GUIDE
RNI
Men and women: 60 mg daily
Sources
Very good sources are citrus fruits, red bell peppers, blackcurrants and guava and papaya. Good sources include strawberries, kiwifruit, broccoli, Brussels sprouts and papaya. If you eat at least five helpings of fruits and vegetables a day, you'll get at least ! 20 rng of vitamin C -twice the RNI.
Signs of Deficiency
Easy bruising (capillary fragility), bleeding gums, muscular weakness, swollen or painful joints, nosebleeds, frequent infections, slow healing of wounds.
Possible Toxicity Problems
Considered quite safe, even in large amounts, since the body simply excretes any vitamin C it can't use. Doses as low as 500 mg can cause .diarrhoea in a few people, but many people can take much larger aoses wun no problems. In one study, however, two of nine people taking 2,000 mg of vitamin C a day suffered with a dry nose and nosebleeds.
People prone to gout or kidney stones, or people with kidney disease, should take large amounts only under medical supervision. Scurvy has been reported in one case where a man taking 1,000 mg a day of vitamin C abruptly stopped taking this supplement in view of the millions now taking this vitamin, on and off.
