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Press releases Saturday 25 March 2006

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(1) EVIDENCE FOR OMEGA 3 FATS LESS CONCLUSIVE THAN WE THOUGHT, SAY EXPERTS

(2) QUESTIONS OVER ACCURACY OF MRI IN DIAGNOSING MULTIPLE SCLEROSIS

(3) DO BICYCLE HELMET LAWS PREVENT HEAD INJURIES AND IMPROVE HEALTH?

(4) TIME FOR BRITAIN TO ADOPT UNIVERSAL HEPATITIS B IMMUNISATION

(5) ETHNIC GROUPS NEED SPECIALIST SERVICES TO TACKLE ALCOHOL MISUSE

(1) EVIDENCE FOR OMEGA 3 FATS LESS CONCLUSIVE THAN WE THOUGHT, SAY EXPERTS

Online First
(Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review)
http://bmj.bmjjournals.com/cgi/rapidpdf/bmj.38755.366331.2F

Online First
(Editorial: Oliy fish and omega 3 fat supplements)
http://bmj.bmjjournals.com/cgi/rapidpdf/bmj.38798.680185.47

A study published online by the BMJ today doesn't find evidence of a clear benefit of omega 3 fats on health.

These findings do not rule out an important effect of omega 3 fats, but suggest that the evidence should be reviewed regularly, say the researchers.

Consumption of long chain omega 3 fatty acids, found in oily fish and fish oils, and a shorter chain omega 3, found in some plant oils, is thought to protect against heart disease. UK guidelines encourage the general public to eat more oily fish, and higher amounts are advised after a heart attack.

Researchers analysed 89 studies (48 randomised controlled trials and 41 cohort studies) to assess the health effects of long and short chain omega 3 fats on total mortality, cardiovascular events, cancer, and strokes.

Each study involved a treatment group and a control group and investigated the effect of omega 3 intake on health for at least six months. Differences in study quality were taken into account to identify and minimise bias.

Pooling the results showed no strong evidence that omega 3 fats have an effect on total mortality or combined cardiovascular events. The few studies at low risk of bias were more consistent, but they also showed no effect of omega 3 on total mortality or cardiovascular events.

When data on long chain omega 3 fats were analysed separately, total mortality and cardiovascular events were not reduced. No study showed increased risk of cancer or stroke with higher intake of omega 3, but there were too few events to rule out important effects.

Other recent reviews of omega 3 trials found that omega 3 fats decrease mortality, but the publication of a large contradictory trial has changed the overall picture. The authors cannot say exactly why the results of this trial differ from the other large studies in this field.

They therefore conclude that it is not clear whether long chain or short chain omega 3 fats (together or separately) reduce or increase total mortality, cardiovascular events, cancer, or strokes.

UK guidelines advising people to eat more oily fish should continue at present but the evidence should be reviewed regularly, say the authors. However, it is probably not appropriate to recommend a high intake of omega 3 fats for people who have angina but have not had a heart attack.

To understand the effects of omega 3 fats on health, we need more high quality randomised controlled trials of long duration that also report the associated harms, they conclude.

We are faced with a paradox, says Eric Brunner in an accompanying editorial. Health recommendations advise increased consumption of oily fish and fish oils. However, industrial fishing has depleted the world's fish stocks by some 90% since 1950, and rising fish prices reduce affordability particularly for people with low incomes.

Global production trends suggest that, although fish farming is expanding rapidly, we probably do not have a sustainable supply of long chain omega 3 fats, he warns.

Contacts:

Paper: Lee Hooper, Lecturer, School of Medicine, Health Policy and Practice, University of East Anglia, Norwich, UK
Email: l.hooper@uea.ac.uk

Editorial: Eric Brunner, Reader in Epidemiology and Public Health, Royal Free and University College London Medical School, London, UK
Email: e.brunner@ucl.ac.uk

(2) QUESTIONS OVER ACCURACY OF MRI IN DIAGNOSING MULTIPLE SCLEROSIS

Online First
(Accuracy of magnetic resonance imaging for the diagnosis of multiple sclerosis: systematic review)
http://bmj.bmjjournals.com/cgi/rapidpdf/10.1136/bmj.38771.583796.7C

The accuracy of magnetic resonance imaging (MRI) is not sufficient to rule in or rule out a diagnosis of MS with a high degree of certainty, finds a study published online by the BMJ today.

MRI has been adopted in England and Wales by the National Institute for Health and Clinical Excellence (NICE) as part of the recommended criteria for diagnosing multiple sclerosis. Although its accuracy has been assessed, the evidence has not previously been systematically assessed.

Researchers analysed 29 studies to assess the accuracy of magnetic resonance imaging criteria for the early diagnosis of multiple sclerosis in patients with suspected disease. Each study compared MRI criteria to a reference standard for the diagnosis of multiple sclerosis. The average duration of follow-up ranged from seven months to 14 years.

Considerable weaknesses existed in the studies included in the review, and studies with methodological flaws overestimated the diagnostic accuracy of MRI.

Only two studies followed patients for more than 10 years, and these suggested that the role of magnetic resonance imaging either in ruling in or ruling out multiple sclerosis is limited. Patients with a first attack suggestive of MS have around a 60% probability of developing MS, this is increased to between 75 and 84% in those with a positive MRI scan and decreased to between 43 and 57% in those with a negative scan over 10-14 years.

The results suggest that use of magnetic resonance imaging to confirm multiple sclerosis on the basis of a single attack of neurological dysfunction may lead to over-diagnosis and over-treatment.

“There is a real danger of giving patients a serious diagnosis which will affect their lives but may turn out to be incorrect later on,” says Penny Whiting.

Dr Jonathan Sterne adds: “Neurologists should discuss potential consequences of false positive and false negative magnetic resonance imaging results with their patients.”

Contacts:

Penny Whiting, Research Fellow, MRC Health Services Research Collaboration, Department of Social Medicine, Bristol, UK
Email: penny.whiting@bristol.ac.uk

or

Jonathan Sterne, Reader in Medical Statistics and Epidemiology, MRC Health Services Research Collaboration, Department of Social Medicine, Bristol, UK
Email: jonathan.sterne@bristol.ac.uk

(3) DO BICYCLE HELMET LAWS PREVENT HEAD INJURIES AND IMPROVE HEALTH?

(Do enforced bicycle helmet laws improve public health?)
http://bmj.com/cgi/content/full/332/7543/722

Many doctors believe that enforced bicycle helmet laws improve health, but this view remains hotly contested in some quarters. Experts in this week’s BMJ set out their arguments for and against legislation.

Several studies suggest that cyclists who choose to wear helmets have fewer head injuries than non-wearers. But Dorothy Robinson, Senior Statistician at the University of New England, New South Wales, Australia, argues that there is no clear evidence that bicycle laws improve public health.

She reviewed data from countries that have legalised the wearing of helmets and believes that the data indicate that helmet laws discourage cycling and produce no obvious response in percentage of head injuries.

For example, in New South Wales, legalisation increased adult use of helmets from 26% in 1990 to 77% and 85% in 1991 and 1992. Yet, she argues, the rate of decline of head injuries did not change.

This contradiction may be due to risk compensation, incorrect helmet wearing, reduced safety in numbers (injury rates per cyclist are lower when more people cycle), or bias in case-control studies, says Robinson.

She suggests that helmet laws are counterproductive and that governments should focus on factors such as speeding, drink-driving, failure to obey road rules, poor road design, and cycling without lights at night.

Robinson’s arguments against helmet legislation are flawed, argue four professors of epidemiology from Canada and the US.

They challenge her interpretation of the data she presents and point to several independent studies showing a protective association between wearing bicycle helmets and head injuries. They also refer to studies showing a reduction in head injuries after helmet legislation was enacted.

Their analyses of the data from New South Wales show that, as the proportion of helmeted cyclists increases, the proportion of bicycle related head injuries decreases.

They also question Robinson’s preference for time series studies which address populations, as opposed to case-control studies, which involve individuals, arguing that the latter provide much stronger evidence. The North American experts dismiss her argument for risk compensation as “pure speculation.”

Finally, they conclude that, without data about how long and how fast riders who quit rather than wear helmets following legislation, “Robinson cannot conclude that decreases in cycling are harmful to health.”

Contacts:

Dorothy Robinson, Senior Statistician, University of New England, New South Wales, Australia
Email: drobinso@aanet.com.au

Barry Pless, Professor of Paediatrics, Epidemiology, and Biostatistics, Montreal Children’s Hospital Research Institute, Montreal, Canada
Email: barry.pless@mcgill.ca

(4) TIME FOR BRITAIN TO ADOPT UNIVERSAL HEPATITIS B IMMUNISATION

Online First
(Editorial: Hepatitis B immunisation in Britain: time to change?)
http://bmj.bmjjournals.com/cgi/rapidpdf/bmj.38797.621516.47

It’s time for Britain to adopt universal hepatitis B immunisation, say senior doctors in an editorial published online by the BMJ today.

The United Kingdom is one of the few developed countries that have not implemented universal immunisation. Instead, it follows a policy of selective immunisation of high-risk groups, and screening all women attending antenatal clinics.

But this approach has come in for some criticism. So, is the British selective programme effective and should the UK now adopt universal immunisation against hepatitis B, ask the authors?

Although the UK has one of the lowest incidences of hepatitis B infection worldwide, the Health Protection Agency estimated that only 44% of infections are potentially preventable under the current programme.

Of particular importance is the average net immigration of about 6,500 people with chronic hepatitis B infection each year between 1996 and 2000, say the authors. This total is cumulative, and therefore the pool is increasing.

For example, in Ireland, the incidence of hepatitis B infection increased markedly between 1997 and 2003, in part reflecting migration from countries with high rates of infection.

However, they warn that targeting vaccination at immigrants could be seen as stigmatising and divisive. Instead, they suggest that, as population movements increase, control of infectious diseases must be supported by regional and global strategies.

Several European countries now include hepatitis B vaccine in their infant immunisation programmes. Alternatively, vaccinating adolescents has been shown to be acceptable and effective.

Would universal vaccination against hepatitis B in the United Kingdom be too costly?

Most cost benefit studies were done before prices were influenced by global markets, say the authors. The full economic burden of hepatitis B still needs to be established but, if direct costs can be reduced by negotiated tendering, there can no longer be a financial argument against adopting a universal immunisation strategy against hepatitis B in the United Kingdom, they conclude.

Contact:

Jangu Banatvala, Emeritus Professor of Clinical Virology, King’s College London School of Medicine, London, UK
Email: jangu@btopenworld.com

(5) ETHNIC GROUPS NEED SPECIALIST SERVICES TO TACKLE ALCOHOL MISUSE

(Editorial: Alcohol misuse and ethnicity)
http://bmj.com/cgi/content/full/332/7543/682

Ethnic minorities may have particular problems with alcohol use, yet may not be seeking help, warns a senior psychiatrist in this week’s BMJ. He believes that these hidden populations need specific services – and more research.

In the United Kingdom, several ethnic minorities have higher levels of alcohol use and resulting health problems than the general population, writes Rahul Rao of the South London and Maudsley NHS Trust.

For example, 34% of Irish men drink above the weekly recommended limit of 21 units of alcohol, compared with 29% of the general Irish population and 27% of the general British population. A similar problem exists in south Asian (Sikh) male migrants to the UK and Hispanic men in the United States.

Both alcohol misuse and ethnicity are bound to social disadvantage, says the author. Considerable stigma also surrounds alcohol misuse in minority ethnic groups, particularly for Asian communities in the UK, where people from an older generation are unwilling to recognise alcohol misuse within their communities.

As a result, people with alcohol problems may try to cope on their own rather than use alcohol services, or they may be unaware of alcohol services. In turn, health providers may avoid developing services for ethnic minorities.

Alcohol misuse cannot simply be tackled using a broad population approach without culturally appropriate services to meet the needs of minority ethnic groups, he writes. This in turn cannot be achieved without a knowledge base drawn from high quality research within specific populations.

Some progress has been made in developing culturally appropriate services over the past 10 years. But at present, such knowledge remains patchy, he concludes.

Contact:

Rahul Rao, Consultant and Honorary Senior Lecturer in Psychiatry, South London and Maudsley NHS Trust and Institute of Psychiatry, London, UK
Email: tony.rao@kcl.ac.uk

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