Intended for healthcare professionals

Rapid response to:


Red meat increases risk of colorectal cancer

BMJ 2005; 330 doi: (Published 16 June 2005) Cite this as: BMJ 2005;330:1406

Rapid Response:

Cohort study, Correlation, and Causality

Dear editor,

The cohort study about the association between red meat, processing
meat, fish consumption and the risk of developing colorectal cancer, has a
huge cohort, excellent methods to measure exposure, incident, and great
data collect and analyse methods[1] Moreover I feel it is one of the best
cohort studies.

The contribution of this cohort study would be confirming a direction
for further investigation, and providing strong evidence supporting that
there is association between red meat/ processing meat consumption and the
risk of developing colorectal cancer among humans.

However causal relationships are unable/ unrealistic to be
established based on only non-experimental studies even they are
perfect(technically non-experimental study can never be perfect). Cohort
studies as well as other non—experimental studies do have their limit. For
example, if people who are genetically more likely to develop colorectal
cancer, genetically prefer the taste of red meat/ processing meat rather
than the taste of any other food—'food preference and higher risk of
developing colorectal cancers are brothers rather than son and dad'.
Though this explanation is hardly based on any ground but logically the
result of the cohort study does also support this ‘hypothesis’.

Thus I believe it would be a good idea for the public to have such an
idea that causal relationships can not be proved by cohort studies, case-
control studies and other non-experimental studies.


1 Norat, T. et al Meat, Fish, and Colorectal Cancer Risk: The
European Prospective Investigation into Cancer and Nutrition Journal of
the National Cancer Institute, 2005 Vol. 97, No. 12.

Competing interests:
None declared

Competing interests: No competing interests

23 June 2005
Wen Bin Liang
Taking master of public health
Curtin University of Technology