Smokers who ingest vitamin supplements containing beta-carotene have a greater risk of developing lung cancer, a British cancer charity has warned.

The Cancer Research Campaign has called for warnings on vitamin supplements containing beta-carotene, which can be obtained naturally in tomatoes and carrots. Natural beta-carotene, however, does not carry the risks of beta-carotene in vitamin supplements.

Professor Gordon McVie of the cancer charity said medical experts can't explain why there is a difference between beta-carotene in supplements and natural beta-carotene. As for the dangers of beta-carotene in vitamin pills, McVie says:

"My advice to smokers, who can't kick the habit, is don't add to your risk of getting cancer by taking beta-carotene supplements. The research is cast-iron in my view and I feel certain most smokers are not aware of the risk."

The New England Journal of Medicine published a study of 29,000 smokers in Finland that showed an 18 per cent higher risk of lung cancer in smokers who used supplements containing beta-carotene.

Similar research in the United States showed an increased risk of lung cancer for asbestos workers who received beta-carotene from supplements.