When is a medical advance a breakthrough? Earlier this month, doctors at King's College Hospital declared a breakthrough in the search for a cure for diabetes as they announced the first patient to become insulin-free following an islet-cell transplant. But is it a breakthrough? The first such transplant to achieve similar success was carried out in Canada more than five years ago, and the prospect that the operation will help more than a handful of people is still a distant dream.

Breakthroughs in medicine can only be seen with hindsight - often from a perspective of decades. But sometimes there is a sense of the ground shifting. I felt that last week over the vitamin D and sunshine story - which is, incidentally, implicated in diabetes. We reported on these pages that the Cancer Council of Australia had issued a statement saying that a "balance had to be struck" between getting enough sun to generate sufficient vitamin D and not getting so much so that it caused skin cancer.

This was remarkable enough from a country where the sun is notoriously fierce, which has some of the highest skin cancer rates in the world, and which for the last three decades has been preaching sun avoidance in a manner that has been copied around the world. If there is a problem of Vitamin D deficiency there, then what can it be like in Britain?

But what caught me by surprise was the response from the cancer community here. A year ago, when the first rumblings about vitamin D deficiency and its potential role in diseases surfaced, the response from cancer organisations was dismissive: there was no evidence of vitamin D deficiency, and to suggest that sun exposure might be good bordered on the irresponsible.

This time, the response was markedly more positive. There was growing interest from the scientific community in the question of vitamin D, Cancer Research UK admitted, and it did mean warnings about sun exposure and the risks of skin cancer had to be carefully targeted at those most at risk - redheads, those with fair skin or with many moles on their skin.

Nor is this a development peculiar to Australia and the UK. The World Health Organisation is planning a meeting to discuss the latest scientific evidence surrounding vitamin D.

In Britain, one of the chief agitators on the issue has been Oliver Gillie, who published a book last year which assembled the evidence for vitamin D's role in illnesses ranging from osteoporosis to diabetes, and to cancer.

Gillie was, initially, dismissed as a troublemaker. His letters to Cancer Research UK, suggesting they looked into the matter, went unanswered. But recent developments suggest his time may have come. Sir Richard Doll, Britain's foremost epidemiologist, who established the link between smoking and lung cancer, is collaborating with Gillie and Julian Peto, a cancer epidemiologist, on a possible study of vitamin D.

The controversy has also reached MPs. Ian Gibson, the chairman of the Commons science and technology committee, has raised the issue with ministers and lobbied the Chief Medical Officer, Sir Liam Donaldson.

I am not a betting man but, if I were, I would lay money we will hear a deal more about vitamin D and sunshine before long.