Vitamin C
In tablet form, vitamin C (ascorbic acid) is the most popular individual vitamin sold in Australia. Vitamin C is essential for good health, but as with all nutrients, more is not better and many top researchers question the wisdom of taking too much vitamin C.
Cold preventative?
Two-thirds of the public believe vitamin C prevents colds, and in winter many people take a daily dose of 500mg or more. A recent analysis of 30 good studies found doses as high as one gram a day had no consistent beneficial effect in preventing colds. However, if you take vitamin C at the first sign of a cold you may reduce the duration of your symptoms by about a day.
Reverse action
Vitamin C is an anti-oxidant, mopping up free radicals which can otherwise damage tissues. However, substances that act as anti-oxidants can reverse their action and become pro-oxidants if taken in very high doses. Some researchers believe this may occur with vitamin C. Dr Ian Podmore, of the University of Leicester in England, reported in the journal ‘Nature’ that volunteers taking 500mg of vitamin C a day for six weeks had higher levels of a chemical which indicates DNA damage in their white blood cells. Another recent study from Dr James Dwyer of the University of Southern California shows that the artery walls of 40 to 60 year olds who took 500mg of vitamin C a day for a year thickened at more than twice the rate of those who did not use supplements. While this is preliminary evidence and is different from the findings of some earlier studies, it may be foolish to take large doses of vitamin C until we fully understand all the implications of doing so. Chewable vitamin C tablets can also damage tooth enamel, whether they contain sugar or not, because they are so acidic.
Health authorities in the United States have introduced an upper safe limit of 2000mg per day, with recommend daily intakes of 75mg for women and 90mg for men. Australia’s recommended levels are currently set at 30mg to 60mg per day. Some people think that is not enough, but the average Australian already consumes more than twice the higher amount. Cigarettes produce harmful free radicals and smokers need about 35mg more vitamin C than everybody else (about the amount you’d get in half a small orange).
Sources of vitamin C
Tablets: some have as much as a 1000mg per tablet which is very high. Even a typical vitamin C tablet with 500mg (equal to about five oranges) is far more than your body needs, and the excess is excreted through the kidneys. Taking more than 2000 mg a day will usually cause diarrhoea which can decrease absorption of other nutrients.
Fruit juices: an excellent source with 80 to 100mg of vitamin C per glass. Eating fruit gives the added advantage of providing fibre that is usually missing from juice.
Vegetables: potatoes are a reliable source of vitamin C, and half a capsicum has several day’s requirements of vitamin C.
Rosemary’s recommendation
The simplest and safest way to get your daily intake of vitamin C (plus some other protective nutrients) is to eat two servings of fruit and five of vegetables. A serving of fruit is a piece equivalent in size to an apple or orange; a serving of vegetable is either half a cup cooked or one cup of salad or raw vegetables. Remember that no tablet can ever make the same nutritional contribution as eating real food.
Further information
See also Rosemary Stanton’s book ‘Vitamins’, published by Allen & Unwin. RRP $14.95.