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BMJ. 2007 December 1; 335(7630): 1116.
PMCID: PMC2099540

Studies of environmental causes of disease need to be more rigorous, leading scientists say

Researchers and policy makers should make greater use of observational studies to identify environmental and lifestyle causes of disease, a report by leading UK scientists recommended this week. But the design of studies needs to be improved for a better understanding of causal pathways, it says.

The study assessed evidence on the use and interpretation of research in the field, reviewed the literature, and held workshops involving a wide range of stakeholders. “The evidence is clear cut,” the report says. “Environmental influences are both strong and important in the causal processes leading to most common diseases. Nevertheless, the knowledge on the specifics of environmental influences, and of the biological pathways through which they exert their causal effects, is decidedly limited.”

The authors, a working group from the Academy of Medical Sciences (an independent group of medical scientists from hospitals, academia, industry, and the public service), warned, “Scarcely a day goes by without some new report of a study claiming to have discovered a new important environmental cause of disease.

“The problem is that few of these findings are confirmed by subsequent research, and, occasionally, new studies even find the opposite. If many of these causal claims turn out to be mistaken, how should we decide what to believe and when to take action?”

Too much emphasis has been given to trying to identify the “single basic cause” of disease, the report says. The working group considered that this type of research was not responding to the right question, as most common diseases involve several environmental and genetic causes.

Instead, researchers should be asking whether a specific environmental factor has a true causal effect that contributes to the development of a disease, so that the disease would be less prevalent if that factor were absent.

The authors gave examples of non-experimental research studies that had made misleading claims about causes, including the finding that caffeine consumption during pregnancy increased the risk of low birth weight babies.

The working group says that priority should be given to high quality research designs that could help identify the environmental components of the causal pathways that lead to disease. This type of observational research can make an important contribution to formulating public health policy and treatment of individual patients, the report concludes. However, policy makers must assess the strength and reliability of evidence before using it to develop public policy and should integrate pilot stages into the implementation of all new policies.

Michael Rutter, vice president of the academy and chairman of the working group, said, “Policy makers often have to make public health decisions very quickly, using existing evidence rather than waiting for further research. It is therefore imperative that rigorous piloting is included in the implementation of new policies and practice. Such piloting may indicate the desirability of modifying the new policy, and, occasionally, even the need for a complete rethink.”

The group set out new guidelines to improve the quality of research into the environmental causes of disease, which include considering the relative merits and limitations of different research designs and planning to get the best possible groups for comparison. Analyses should be planned to avoid later dredging of data and should be adequately statistically powered. Researchers should pay careful attention to other research when reporting findings and should “resist any pressures . . . to exaggerate the claims.”

Notes

Identifying the Environmental Causes of Disease: How Should We Decide What to Believe and When to Take Action? is available at www.acmedsci.ac.uk/publications.


Articles from The BMJ are provided here courtesy of BMJ Publishing Group