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Does taking vitamin C really shorten the duration of a cold?
The effect of vitamin C on the symptoms of the common cold is quite confusing, but taking large doses does seem to shorten the duration of the cold by perhaps around 10-20%. The amount of vitamin C required to produce this effect is still unclear. In trials where vitamin C has been given after the cold symptoms have started, there is some evidence that taking larger doses is more beneficial.
Large doses of vitamin C can have adverse affects and you should consult your doctor before taking large doses of any vitamin.
Does food that contains beta-carotene put me at increased risk from lung cancer?
No. The evidence of a potential harmful effect of beta-carotene is from two clinical trials where high dose beta-carotene supplements were given to smokers and other people at high risk of developing lung cancer. There is no evidence to suggest that the amount of beta-carotene found in food presents any risk. In fact, the evidence is the opposite. People who have a diet rich in beta-carotene have been found to be less likely to develop lung cancer.
Do vitamin E supplements prevent heart disease?
This remains one of the biggest questions in vitamin science. Studies have shown that people who have a diet containing lots of vitamin E, including from supplements, are less likely to develop heart disease. The problem is that nobody knows whether it really is the vitamin E that is having the beneficial effect.
Clinical trials investigating the use of vitamin E on heart disease have produced mixed and often disappointing results. Those in favour of vitamin E argue that these trials have been conducted in people who already have heart disease, and that the real benefit of vitamin E is in long term prevention and this theory hasn't been tested properly.
Everybody agrees that eating a diet rich in vitamin E is good for you, but the benefit of taking vitamin E supplements to prevent heart disease remains open to question.
Taken in large doses vitamin E can have side effects and you should consult your doctor before taking any supplements.
How much vitamin A is it safe for me to eat?
At the moment, the safe level of vitamin A consumption is the source of fierce debate. There has been evidence linking high intakes of vitamin A with an increased risk of bone fracture, but not all studies have found this link.
In 2003, a large safety review by a team of experts in the UK said that they could not define a safe maximum intake, but they cautioned people about long term consumption of more than 1,500 microgrammes per day.
The link between vitamin A consumption and bone fracture relates to vitamin A in the form of retinol (often just called vitamin A). It is not linked to the consumption of beta-carotene that your body converts into vitamin A.
Do you only get vitamin A in high dose supplements?
No. Vitamin A is found in food, particularly liver, oily fish and dairy products. Many one-a-day multivitamins also contain about 800 microgrammes of vitamin A. Another common source is cod liver oil.
If you are concerned about the amount of vitamin A you consume you should discuss it with your doctor.
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