American oncologists keen to add cancer to the list of dangers from obesity, poised to overtake smoking as a 'primary' cause.

There are few more publicly emotive words in the medical lexicon than ‘causes cancer’.

It is the clinical equivalent of shouting ‘fire’ in a theatre and induces the same visceral response in each of us; does that mean me?

Well if you are one of the estimated 25% of the UK population who, like me, has a body mass index of something over 25 then yes, I’m afraid they do mean us.

Not content with horror stories of heart attacks and strokes and losing limbs from type 2 diabetes, we are now being told that obesity causes cancer.

Not only that, but they suggest that if you are overweight and develop cancer you stand a much greater risk of dying from the disease than more svelte fellow sufferers.

Now I’m not saying for an instant that it’s a good thing to be overweight.

We should all try and moderate our diet and take regular exercise to stay healthy.

I am saying that neither public policy nor personal peace of mind is well served by the kind of ‘sky falling in’ rhetoric that is being employed not only by the press in this instance, but by the oncologists themselves.

It’s as if they believe that fat people have hitherto decided to risk heart disease and diabetes but might change their minds at the inclusion of cancer and say “ok then I won’t be fat any more”.

The figures they quote are certainly scary.

They claim that one in every five cancer deaths is ‘caused’ by obesity and accelerates the onset of cancer by some 20 years, so a condition that might not have developed until 80 might emerge in an obese person at 60.

The researchers went on to further claim that obese women with breast cancer were 75 per cent more likely to die and that very overweight women were six times more likely to develop womb cancers.

The nub of the arguments put forward by these doomsday presentations is that weight may overtake smoking as the primary cause of cancer and that diet and exercise should form part of any treatment of cancer in overweight patients.

In fact smoking was linked to some 78,000 deaths from cancer in 2013 but showed a reduction of nearly 20% from the 95,000 smoking related deaths a decade earlier.

That would represent about 23% of all cancer deaths in the UK, still a long way ahead of the 5% attributed to obesity by Cancer UK or even the 10% ‘caused’ by obesity according to the American oncologists.

Of course as, hopefully, smoking continues to reduce in impact it is a function of mathematics that other causes will increase.

Actually the link between excess weight and cancer has already been suggested by a variety of studies, mostly suggesting that the hormone imbalances caused by obesity feed the growth of cancer cells and make treatments like chemo and radiation far more problematic.

We should all know that being overweight means we are unhealthy and being unhealthy will only magnify the potential of cancers to cause damage.

Do we really need to be shouting ‘fire’ and increasing the potential anxiety already caused by weight gain which study after study has linked to depression?

As it turns out, the American claims are projections, not measurements, and are based on the extrapolation of existing data using computer models they created specifically for the purpose.

But that doesn't make them right and even a cursory glance at the arithmetic of our current situation should give pause.

According to Cancer UK obesity causes an estimated 5% of all cancer cases in the UK, which would mean around 16,500 out of 330,000 (2011) not the 33,000 (10%) that the Americans claim.

Around 60% of the UK population is overweight, 25% of them obese which means of some 16.2 million at risk, of whom slightly more than 1% developed cancer as a result of their weight.

Even extrapolated over several decades this doesn’t indicate any measurably greater risk than officially quoted lifetime risk of 50% for any man or woman born after 1960 already quoted by Cancer UK.

Of course if more of us are obese, more cancer patients will be obese anyway without any causal link; so while it may provide a handy and elegant solution to the question ‘what causes cancer?’ I fear that we may be leaping to conclusions again.

Just as we appear to have done with the important question ‘what causes obesity?’.


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