Vitamin C 'may harm as well as heal'

Vitamin supplements are increasingly popular

Vitamin C may be capable of actually causing damage to cells that could potentially lead to cancer as well as protecting them, laboratory tests suggest.

It is well known that taking vitamin C in large doses may harm humans, but it is thought that smaller supplements are beneficial.

We seem to have the idea that if something is good for you then more must be better, but that is not always the case

Dr Wendy Doyle

In particular, it is recommended for its ability to help the body "mop up" particles which can cause gene damage.

However, researchers at the Center for Cancer Pharmacology at the University of Pennsylvania studied the effects of a moderate dose of the vitamin on lipid hydroperoxides, substances that occur naturally in human tissue.

They found the presence of the vitamin made it decompose into substances called genotoxins.

Mutations

These have been blamed for causing mutations in the genetic structure of individual cells, and are suspected of contributing to cancerous changes in some cases.

Author of the study, Ian Blair, said this did not necessarily mean that vitamin C could cause cancer.

He said: "It's possible that vitamin C isn't working in cancer prevention studies because it's causing as much damage as it's preventing, but that's really speculation at this point."

He said that while a diet rich in fruit and vegetables did prevent cancer, it might be a combination of ingredients, not just vitamin C.

However, some nutritionists remain unconvinced by the results, pointing out that they were conducted in a test tube rather than a real human cell, so may not accurately reflect what goes on in the body.

Enzymes

A spokeswoman for the British Nutrition Foundation said that additionally, there were enzymes in the body to remove the damaging genotoxins.

She added: "Whilst populations which have a high fruit and vegetable intake are consistently found to have lower rates of cancer and heart disease, the results of supplementation studies (with vitamin C) have been very disappointing.

"There is, however, no evidence that those who choose to consume vitamin C supplements increase their risk of these conditions."

Dr Wendy Doyle, from the British Dietetic Association, told the BBC that while the study should be taken seriously, a lot more research needed to be done before firm conclusions could be made.

"We seem to have the idea that if something is good for you then more must be better, but that is not always the case, particularly with supplements."

She added that it was better to eat fresh fruit and vegetables because they contained other beneficial chemicals apart from vitamins and minerals.

She said if somebody was worried about their diet, the best supplement to take was an all-round multi-vitamin.

No cause for concern

The Proprietary Association of Great Britain said the study should not cause concern for the many people who benefit from taking vitamin C supplements.

In a statement, the association said: "This study was performed in test tubes and not in the body.

"Because of this, it doesn't take into account that the body naturally eliminates any unwanted toxins that may be formed from using vitamin C to perform necessary functions.

"Also, in the body, vitamin C is kept separate from the lipid molecules that the study suggests interact with it."

The research was reported in the journal Science.