How far do politicians allow the media to influence their views on health policy? And can a flurry of news stories about an alleged risk to health influence public behaviour? If so, is the public interest well served? These questions prompted a study by the King's Fund, which investigates the relationship between patterns of news coverage of health stories and degrees of risk to public health.

A series of interviews with health experts and policy-makers revealed almost universal dissatisfaction with the way health-related matters were covered in the news media. Issues that were genuinely important, such as smoking and mental health, were routinely neglected, they said. Meanwhile issues that posed minimal risks ? such as the alleged link between the MMR vaccine and autism, and stories about the NHS in crisis ? were given undue prominence.

The King's Fund study includes an analysis of health-related stories by three BBC news programmes and three newspapers ? the Daily Mirror, the Daily Mail and the Guardian. In all six outlets it found a heavy majority of news in two categories: stories about the NHS ? mostly about crises besetting the service; and health "scares" ? that is, risks to public health that were widely reported but killed very few people. The "big killers" such as smoking, alcohol, obesity and mental health received little or no attention. Indeed, there was an inverse correlation between severity of risk and volume of news coverage. For example, 8,571 people died from smoking for each news story on the health risks of smoking, compared with 0.33 deaths for each story on vCJD (the human variant of "mad cow" disease).

But how much does this matter? Most of those interviewed shared the view that the media could exert a powerful influence over human behaviour and the policy making process. A similar concern has prompted the Royal Society to launch an inquiry into the way scientific research findings are reported since "highly questionable results" could, the society maintains, have "quite profound effects on public opinion and policy".

There is evidence that health "scares" fuelled by heavy media attention have led significant numbers of people to change their behaviour in ways that may have increased the risk of illness. For example, stories about a link between the MMR vaccine and autism led to a 12 per cent drop in take up of the vaccine, so that by 2001/2 nearly half a million children had not been vaccinated against measles. The fact that most scientists disputed the alleged risk of autism, and supported the vaccine because measles posed a much bigger threat to children's health, was not widely reported at the time. The study points out that conventions of news reporting, especially in broadcasting, favour the juxtaposition of opposing views, typically from two "experts" who are invited to put their side of the argument. This format gives an impression of balance but fails to reflect the weight of evidence.

Few could doubt, especially in the light of the Hutton inquiry, that politicians pay close attention to the news media. The study shows how politicians and news reporters reinforce each other's messages in ways that may not necessarily benefit public health. For example, a preponderance of news about people being kept waiting for NHS treatment may prompt the government to give higher priority to cutting waiting times and this may in turn encourage some news media to find yet more stories about health service queues. The more headlines there are, the greater the pressure on policy makers to focus on waiting times. "Resources may be invested accordingly ? possibly at the expense of other health-related issues that bring greater benefit at less cost."

The NHS Plan, with its massive injection of new money into the NHS followed relentless media denigration of the NHS and heightened public concern, fuelled by a succession of stories about the winter "crisis". The dearth of news stories about public health issues such as the impact of poverty, poor housing, social exclusion, smoking, diet and exercise may help to explain the low priority given to public health in government policy at the time of the plan and ever since.

Could ? or should ? things be done differently? The study acknowledges the vital role the media can occasionally play in exposing health risks that are being concealed or overlooked, and in holding the government to account. Interviews with senior journalists and editors shed useful light on how and why certain stories are selected and others are not, and the pressures under which decisions are taken in busy newsrooms. Many of the journalists interviewed insisted that news values ? the criteria by which "news" is selected ? were paramount. However those values varied between news outlets and were interpreted differently by different journalists.

The differences were particularly marked between the BBC, which has obligations as a public service broadcaster, and newspapers, which operate with fewer constraints. The BBC was especially concerned to avoid accusations of "campaigning", as this could be inconsistent with its charter. Yet what constituted campaigning journalism was acknowledged to be a grey area. Pursuit of original stories on a little-reported topic might be dismissed as a campaign, while the "safer" alternative might be to follow up stories initiated by a newspaper such as the Daily Mail, which had no such reservations about campaigning.

There was broad agreement among all interviewees that there could be no direct correlation between what conditions cause the most deaths and what gets most news coverage. Newspapers full of stories about the dangers of smoking would be very dull indeed. But many said there should be more careful handling of health news and more awareness about the links between media coverage and health outcomes.

In response to the report, the BBC has produced guidance to encourage accurate and balanced reporting of risks. What's needed now, the study concludes, is "a vigorous public debate about health, health care, risk and reporting, about the respective roles of different news outlets in communicating health-related issues, and about how to achieve a closer match between proven health risks and news coverage without jeopardising the freedom of the media or their role in holding governments and experts to account".