Not satisfied with his work that unravelled the double helix structure of DNA and landed him a share of a Nobel prize half a century ago, James Watson has come up with a radical theory for diabetes, dementia, heart disease and cancer.

The 85-year-old scientist has turned to the pages of the Lancet medical journal to set forth his grand idea, which some academics say may not have seen the light of day had it come from anyone else.

Watson, who stepped down as director of the Cold Spring Harbour Laboratory in New York in 2007 after the Times quoted his views on Africa and intelligence, has arranged a conference at the lab this year to explore his latest hypothesis.

Writing in the Lancet, Watson claims that late onset, or type 2 diabetes, is traditionally thought to be caused by oxidation in the body that causes inflammation and kills off pancreatic cells. But he thinks the root of that inflammation is quite different: "The fundamental cause, I suggest, is a lack of biological oxidants, not an excess," he writes.

Watson, a keen singles tennis player, says he developed his theory after pondering why exercise seemed to benefit people with high blood sugar, an early indicator of future diabetes. Exercise produced "reactive oxygen species" that were widely thought to be harmful.

Other research fed into his thinking, chiefly a study by Matthias Blüher at the University of Leipzig. He showed that reactive oxygen species released in exercise combatted the insulin resistance seen in diabetes, but that the benefits vanished if you gave people antioxidants before the exercised.

Watson believes that rather than being wholly bad, oxidising molecules, such as hydrogen peroxide, are crucial for the body's health. In particular, he points out that hydrogen peroxide goes to work in a cellular organ called the endoplasmic reticulum, where it ensures proteins are stable. If levels of oxidants are too low, he suggests, the proteins become misshapen and cause the inflammation that damages the pancreas. And a raft of other diseases.

Large studies have already shown that antioxidant supplements do not help people to live longer. Watson's hypothesis also suggests there is nothing to be gained, though he makes a point of saying he is not qualified to give people health advice.

"Just about every doctor I've ever known tells every patient who is capable of doing so to exercise. I think exercise helps us produce healthy, functional proteins. But we really need to have some high-quality research to demonstrate this."

He adds: "We sorely need to take a much more serious and thorough scientific look at the mechanisms through which exercise improves our health."

Watson's idea received a mixed reception from scientists on Thursday. One professor of metabolic medicine was unimpressed and said the idea was not even novel. "It is only because of his name that James Watson is allowed to present his woolly thoughts in the Lancet," he said.

The director of the MRC Metabolic Diseases Unit at the University of Cambridge, Stephen O'Rahilly, was less scathing. He said: "He's exhorting more science to be done on how physical activity might be beneficial. We need to understand the mechanism. Making the right reactive oxygen species in the right place at the right time is critical for us to stay well, and blocking them might not be a good idea." © Guardian News and Media 2014