From Madonna’s quest to “neutralise radiation” to Tom Cruise’s dismissals of psychiatry, celebrities are seldom shy about expressing their views on health and science – even when they appear not to know what they are talking about.

A roll call of public figures such as Cruise and Delia Smith have offered bogus advice or “quackery” this year, according to scientists and doctors. The charity Sense About Science is concerned that celebrities mislead the public when they endorse theories, diets or health products while misrepresenting the science involved.

Some – such as Oprah Winfrey and Kate Moss – espouse “detox” regimes, while others, such as Sharon and Kelly Osbourne, believe (mistakenly) that the Pill can cause cancer.

Nor are politicians exempt from lending credence to health myths. The US President-elect is among several American public figures who continue to suggest that the MMR vaccination is a potential cause of autism, despite an overwhelming weight of scientific evidence to the contrary.

Smith’s suggestion that obesity is caused by sugar addiction is another of the assertions under scrutiny. In March, the cookery writer and broadcaster told The Times: “That’s what causes obesity. It’s addiction. You need to have six weeks without sugar or sweetener . . . After six weeks, everything will taste sweet . . . because you will have got your palate back to what nature created. We could cure the nation if we cut down sugar addiction.”

Lisa Miles, of the British Nutrition Foundation, counters: “Delia, you’ll never get rid of sugar from the diet, nor would you want to, as you consume sugars naturally in foods such as fruit and milk, which provide us with important nutrients . . . the causes of obesity are much more complex.”

Demi Moore, the actress, surprises the experts with her use of “highly trained medical leeches” to “detoxify” her blood.

Kate Moss, the model, is reported to be on a strict “detox” diet of fruit and vegetables at a health spa in Thailand. But nutritionists note that such regimes exclude important food groups such as protein.

Moss’s friend Stella McCartney, the designer, was criticised last year for saying that a chemical found in skin creams was also found in antifreeze. Gary Moss, a pharmacologist, said that the chemical, propylene glycol, was versatile and its use in cosmetics was not “scary”, as claimed.

Both Mr Obama and his rival for the presidency, John McCain, responded to stories about vaccines by highlighting the rise in diagnoses in children of autism.

Mr Obama told a campaign rally in April: “We’ve seen a skyrocketing autism rate. Some people are suspicious that it’s connected to the vaccines. This person included. The science right now is inconclusive, but we have to research it.” In February Mr McCain had remarked on the rise in autism cases, saying that there was “strong evidence that indicates it’s got to do with a preservative in vaccines”.

The suggestion that the MMR jab is linked to the developmental disorder dates back to a study of 12 children published in The Lancet in 1997. The research, led by Andrew Wakefield, a gastroenterologist at the Royal Free Hospital, has since been discredited. Yet fears about the vaccine – for measles, mumps and rubella – have resulted in many parents refusing to have their children inoculated, and there has been a resurgence of measles.

Dr Wakefield and colleagues have been appearing before the General Medical Council on charges of serious professional misconduct, relating to their original study, which they deny.

Studies in several countries involving millions of children have shown no correlation between MMR and autism rates.

Michael Fitzpatrick, author of MMR: What Parents Need to Know, said that Mr Obama and Mr McCain were correct in noting a rise in cases of autism. “However, authoritative studies confirm that the apparent rise is attributable to increased public and professional awareness of the condition and to widening definitions of autistic spectrum disorders,” he said. “Though the causes of autism remain obscure, exhaustive researches have failed to substantiate any link to vaccines or any preservatives in it.”

The Sense About Science initiative is an update of a leaflet encouraging celebrities to avoid making claims until they have checked the facts. While there has been “considerable improvement” in the way British celebrities approach medicine, the charity says its files are still too full of pseudo-scientific claims. “We don’t expect people to know everything about science; the problem comes when they don’t consider checking it or asking questions.”

Explore Health

• Expert Advice

• Health Features

• Mental Health

• Alternative Medicine

• Child Health

• Health Club