Oxford researchers carried out a meta-analysis 0f 57 cohort studies with a total of 894,576 people to examine the relationship between MBI and mortality. Most of the participants were recruited during 1970s and 80s with an average of 8 years further follow up. They were aged 46 in average at enrollment with BMI 24.8kg/sq m ( BMI>30kg/sq m were considered obese).
Researchers found that people with a normal BMI (22.5 - 25kg/sq m) had the lowest overall mortality. Every 5kg/sq m rise in BMI above 25 increased the risk of death by 30% compared with people having normal BMI. They estimated that average lifespan is reduced by 8 - 10 year for people with BMI above 35kg/sq m. The greatest increase in death risk was associated with diabetes, kidney or liver disease, followed by vascular mortality. They concluded that BMI itself is a strong predictor of overall mortality.
Critics say that this research gives actual figures on mortality risk associated with obesity but they argue that the increased death rate cannot be attributed to obesity alone, diabetes, high blood pressure and bad cholesterol are associated particularly with increased risk of cardiovascular mortality with high BMI, also the effects of diet, exercise and socioeconomic status were not taken into acount.
Source: "Body-mass index and cause-specific mortality in 900,000 adults: collaborative analyses of 57 prospective studies". The Lancet 2009; early online publication, March 18
Thursday, March 26, 2009
Should clinical guidelines be avoided completely?
Researchers examined the changes in recommendations in cardiovascular guidelines from 1984 to 2008 issued by the American College of Cardiology (ACC) and the American Heart Association (AHA) and found that the recommendations are often based on lower levels of evidence or expert opinion.
The ACC/AHA guidelines use a grading system based on the level of evidence and class of recommendation. The level of evidenece includes a description of the existence and types of studies supporting the recommendation and expert consensus. The class of recommendation indicates the strength/weakness of the recommendation based on a judgement about the relative merits of the data.
Researchers found that the number of recommendations has increased 48% from the first guideline to the current version, with the biggest increase in class 2 recommendations ( those with conflicting evidence and/or divergent opinions). About half of all recommendations are based on expert opinion or case studies rather than clinical trials or meta analysis. In addition, almost half of the recommendations have a level of evidence C ( lower level with little supporting evidence). Among the class 1 recommendations of guidelines, only 19% have a level of evidence A (higher level). There is also wide variation across all fields of cardiology.
Researchers said that their findings highlight the inadequancy of definitive data for the generation of cardiovascular guidelines and suggested the medical community should focus on areas with deficient research and address practical clinical questions that do not involve new products.
Clinical practice guidelines are often regarded the standard of EBM, but the authors said these recommendations imply also "a value judgement based on personal or organisational preferences regarding the various risks and benefits of a medical intervention for a population", therefore clinicians need to be cautious when considering recommendations not supported by solid evidence.
In an accompanying editorial, the authors warned that guidelines often become marketing tools for pharmaceutical manufacturers as financial ties between guideline committee members and industry are common, their biases, values and goals which influence the recommendations they make are generally not disclosed.
They also argue that current guidelines are not patient-specific enough to be useful and lack flexibility. Many clinicians do not use guidelines because there are too many, often on the same topic and out of date. There is also concern that many guidelines which are expert consensus statements are being used as performance measures to assess the quality of care.
The researchers said if impartial recommendations are to be achieved, major changes including limiting guideline committee members with potential conflicts of interest are needed. They concluded "If all that can be produced are biased, minimally applicable consensus statements, perhaps guidelines should be avoided completely. Unless there is evidence of appropraite changes in the guideline process, clinicians and ploicy makers must reject calls for adherence to guidelines."
Sources:
1) "Scientific Evidence Underlying the ACC/AHA Clinical Practice Guidelines" JAMA. 2009;301(8):831-841
2) Editorial : "Reassessment of Clinical Practice Guidelines - Go Gently Into That Good Night" JAMA. 2009;301(8):868-869
The ACC/AHA guidelines use a grading system based on the level of evidence and class of recommendation. The level of evidenece includes a description of the existence and types of studies supporting the recommendation and expert consensus. The class of recommendation indicates the strength/weakness of the recommendation based on a judgement about the relative merits of the data.
Researchers found that the number of recommendations has increased 48% from the first guideline to the current version, with the biggest increase in class 2 recommendations ( those with conflicting evidence and/or divergent opinions). About half of all recommendations are based on expert opinion or case studies rather than clinical trials or meta analysis. In addition, almost half of the recommendations have a level of evidence C ( lower level with little supporting evidence). Among the class 1 recommendations of guidelines, only 19% have a level of evidence A (higher level). There is also wide variation across all fields of cardiology.
Researchers said that their findings highlight the inadequancy of definitive data for the generation of cardiovascular guidelines and suggested the medical community should focus on areas with deficient research and address practical clinical questions that do not involve new products.
Clinical practice guidelines are often regarded the standard of EBM, but the authors said these recommendations imply also "a value judgement based on personal or organisational preferences regarding the various risks and benefits of a medical intervention for a population", therefore clinicians need to be cautious when considering recommendations not supported by solid evidence.
In an accompanying editorial, the authors warned that guidelines often become marketing tools for pharmaceutical manufacturers as financial ties between guideline committee members and industry are common, their biases, values and goals which influence the recommendations they make are generally not disclosed.
They also argue that current guidelines are not patient-specific enough to be useful and lack flexibility. Many clinicians do not use guidelines because there are too many, often on the same topic and out of date. There is also concern that many guidelines which are expert consensus statements are being used as performance measures to assess the quality of care.
The researchers said if impartial recommendations are to be achieved, major changes including limiting guideline committee members with potential conflicts of interest are needed. They concluded "If all that can be produced are biased, minimally applicable consensus statements, perhaps guidelines should be avoided completely. Unless there is evidence of appropraite changes in the guideline process, clinicians and ploicy makers must reject calls for adherence to guidelines."
Sources:
1) "Scientific Evidence Underlying the ACC/AHA Clinical Practice Guidelines" JAMA. 2009;301(8):831-841
2) Editorial : "Reassessment of Clinical Practice Guidelines - Go Gently Into That Good Night" JAMA. 2009;301(8):868-869
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