Apparently the young are all dying of cancer because they’re all so damn fat. That’s the conclusion to draw from this latest research – the young are showing disturbing incidences of obesity related cancers. Sadly, there’s a logical error here. Or at least a potential logical error. We don’t actually know that the cancers are being caused by obesity. Could be something else. Might, just to invent some reasons, be sugar consumption, lack of exercise or the existence of Simon Cowell. That last has certainly soured a few guts in its time.
Normally this isn’t a problem in epidemiology. We’ve a correlation here and that’s what we’re exploring, obesity rates and cancer rates. But we do have a problem because of the way we decide that a cancer is obesity related. We just assume that some percentage of cancers are, of their type, caused by obesity. Which again is usually fine. But that doesn’t work if we think we’re seeing a structural change in the world. A structural change pretty much being defined by our thinking that we’re seeing a change in the rates of incidence.[perfectpullquote align=”full” bordertop=”false” cite=”” link=”” color=”” class=”” size=””] Rates of obesity-fuelled cancers are now rising in successively younger age groups, a landmark study shows. Experts said “shocking” levels of disease linked to growing waistlines across the globe threaten to reverse decades of progress in the war on cancer. The Lancet study shows that rates of obesity-related cancers are rising faster in adults aged 25 to 49 than in older generations – despite the fact cancer is seen as a disease of old age. The research, which examined 12 types of cancer linked to obesity, divided patients into five-year age groups from 25-29 to 80-84 years old. In six of the main cancers – including bowel, pancreatic and kidney disease – it was found that the younger the age group, the greater the increase in incidence. [/perfectpullquote]
We start by stating that certain cancers are obesity related. As with booze deaths, 25% – or whatever the number – of exploding livers are assigned to booze as a cause. Now we see a rise in exploding livers, we say that booze related exploding livers are rising. By 25% of the total number. But that doesn’t work if there’s some new thing causing livers to explode – say, Hepatitis C, or E,F,G, however far we’ve got in exploring. We can’t and shouldn’t assign 25% of the deaths from that to booze. But we will do, given that we count 25% of all deaths from exploding livers as coming from booze.
We might well be seeing a rise in youth cancers. And they might well be those types of cancer which we associate with obesity. But the next step, the rise in cancer is being caused by the rise in obesity, this isn’t something we can say. Because we’re not actually checking that the cancers are being caused by obesity, we’re assuming it.
Not that that will stop those who insist we should all starve ourselves into being whippets but it’s worth pointing it out.