New research suggesting that vitamin C can be effective in curing cancer will renew interest in the "alternative" treatment for the terminal disease.

Three cancer patients who were given large intravenous doses over a period of several months had their lives extended and their tumours shrunk, doctors reported yesterday.

A 49-year-old man diagnosed with terminal bladder cancer in 1996 was still alive and cancer-free nine years later, having declined chemotherapy and radiotherapy in favour of regular infusions of vitamin C.

A 66-year-old woman with an aggressive lymphoma who had a "dismal prognosis" in 1995 was similarly treated and is still alive 10 years later. A 51-year-old woman with kidney cancer that spread to her lungs diagnosed in 1995 had a normal chest X-ray two years later. The findings were confirmed by pathologists. Although they do not prove the vitamin cured the cancer they do increase the "clinical plausibility" of the idea, the researchers say.

Vitamin C therapy was first promoted by Linus Pauling, the Nobel prize winner, 30 years ago. Dr Pauling's claims sparked the continuing boom in sales of vitamin C, but attempts to confirm his findings failed and high-dose vitamin C became an "alternative" therapy.

The latest study, published in the Canadian Association's Medical Journal, could trigger renewed interest in Dr Pauling's claims. Studies show that vitamin C is toxic to some cancer cells but not to normal cells. The problem has been delivering a high enough dose.

The researchers say attempts to replicate Dr Pauling's work failed because they used oral doses of the drug which is rapidly excreted. However, injections achieve blood levels 25 times higher that persist for longer. At these very high doses, the blood level of vitamin C is high enough to selectively kill cancer cells.

Several clinical trials of vitamin C therapy are about to start, including one at McGill University, Montreal, the authors say.