Because scientists have not been able to pin point exact cause of cancer, other factors, like, life style, food habits and their relation with cancer causation has been a hot area of scientific pursuit. It must be pointed out that scientific reports published in medical journals deal with investigation of milk (or in general, other dietary factors) as a risk factor and NOT AS A CAUSAL FACTOR. However, while reporting in the general newspapers, the terminology is changed (I suspect it to be intentional), obviously to attract attention of unsuspecting public.

To understand the concept of risk factor it is important to understand the disease causal mechanism. The Koch and Henle Postulate in early years were regarded as landmark criteria for establishing the cause of a disease. A draw back of this postulate was that the diseases were wrongfully labeled as due to only a single cause. For example, tuberculosis was regarded to be a disease caused by Mycobacterium tuberculosis (many doctors still do that). However, now it has been shown that mere presence of the tuberculosis bacteria is not sufficient to produce the disease but other factors, such as, malnutrition, breakdown in immunity, etc., are important contributing factors. Thus, Mycobacterium organism is an essential causal component; it becomes sufficient only when other factors are also present. Factors, such as, malnutrition, immune status, etc., will be called risk factors. It would be wrong to indict malnutrition as the cause of tuberculosis. Now, we know that most of the diseases are multi-factorial. Taken these together, the three factors constitute a sufficient causal model. Like this, for each disease there could be more than one sufficient causal model.

While reporting on the involvement of risk factor in a disease, the whole thing is distorted and it is made out as if the risk factor is the cause of the disease. A risk factor by itself is not a sufficient causal factor. The disease can be caused only when several risk factors are present in association with the causal factor. A risk factor however by itself can not cause a disease. While sensationalizing identification of a risk factor this precise difference is deliberately overlooked by the science reporters and such risk factors are wrongly indicted as the causal factor. If the public can appreciate this difference, they would not be misguided by the hype.

This reminds of a "so called" scientific lecture I sat through wherein the learned speaker, a very senior medical scientist, admitted that although he had been smoking since student days, he is hale and hearty, whereas his colleagues who never smoked or drank, died of cancer at a young age. He also cited several examples of families who suffered from cancer although they led pious life. So without a wink he thundered "How smoking can be indicted for cancer?" and added " so friends, go ahead and enjoy your cigarette." This confusion was because he wrongly considered smoking to be the sole cause of cancer, which is not correct. Smoking, at best, would only increase risk of cancer but it is not the sole factor or causal factor for cancer. IF THIS SOUNDS INTERESTING, WE GO AHEAD AND DISCUSS HOW SCIENTISTS IDENTIFY RISK FACTORS FOR A DISEASE.

This science is called Epidemiology and it largely relies on collection of data from a target population and applying mathematical or statistical tests to interpret the data. For example, if a scientist is interested in knowing if milk is a risk factor for prostate cancer, one approach will be to first identify males diagnosed for prostate. Their diet habits, specially, quantity and frequency of milk consumption, is noted by asking questions (in person or through questioner by post). Similar number of healthy males (but otherwise comparable) are also studied as control. The data is then analyzed to find out the proportion of cancer cases that consumed milk or milk products as compared to control. The second approach is to follow up x number of persons (milk consumers and non-milk consumers) over a period of time (generally years) and identify the numbers that develop prostate cancer in both the groups. With this approach the effect of a number of factors, such as, nutrition status, life style, profession, etc. can also be compared. In all such studies the most crucial factor is the way study units have been selected. In many cases, it is random sampling but in some studies (like the second approach), the selection is purposeful. In both the cases, the extrapolation of findings on a larger group of population can not be carried out. For example, if an epidemiological study is done in North America, it necessarily can not be applied for Indian or Asian population. Therefore, next time you read such report in a newspaper first confirm if the study pertains to your country, otherwise the results are only suggestive.

Now let us revert to the issue of prostate cancer. We still do not fully understand how prostate cancer is caused. All we know is that there are several risk factors associated with it. Dr. Chan, an epidemiologist with Harvard School of Public Health whose work is often referred by anti-milk lobby conducted his investigations by collecting diet information about the people who were already undergoing a long-term study. From the data, he deduced that men consuming dairy products and calcium appeared to have moderately higher risk. The researchers postulate that the effect of milk might be mediated through high calcium intake. Thus, a similar moderate increase in risk is likely to be with any another food rich in calcium. The researchers themselves have reported serious constraints with their methodology. Thus, the findings can not be regarded as unequivocal.

"Milk consumption is associated with increase in serum levels of IGF1. Which causes cancer in human."
- Mr. Robert Cohen, Executive Director, Dairy Education Board, New Jersey.