Are you worried about your cancer risk? Are you confused by the studies you see mentioned in the media about how certain substances and behaviors affect our risk of contracting cancer or developing certain diseases?
If so, it’s important that we talk about a concept that will enable you to make sense of the latest news headlines on such and such health study.
The concept is absolute vs. relative risk.
Your absolute risk is your risk of developing cancer or another disease over a specified period.
Your relative risk is the risk that one group of people compared to another group.
For example, smokers are much more likely than non-smokers to develop lung cancer.
About 80 to 90% of lung cancer cases are linked to smoking.
However, that doesn’t mean that a smoker has an 80% chance of developing lung cancer over a lifetime.
But compared to non-smokers, smokers are 15 to 30 times more likely to get cancer than non-smokers.
That’s the relative risk. So the risk of lung cancers in smokers relative to the risk of non-smokers.
The absolute risk of a smoker contracting lung cancer depends on a lot of factors, but the number will be much lower than the relative risk. It might be 10 to 20%, for example.
That means that an individual smoker may have a 10% absolute risk of getting lung cancer.
A non-smoker might have a 0.3% of getting lung cancer in absolute terms.
Alcohol and Cancer
Let’s say that we hear that drinking a beer every day increases your chance of getting colon cancer by 10%.
Again, that does not mean that any drinker has a 10% of getting this cancer.
Because the overall risk of getting this type cancer may be only 10%, an increase of 10% in drinkers means that their absolute risk is now 11%, instead of 10% before.
Meat and Cancer
Recently, the WHO has put processed meat in the “known carcinogen category.” They wrote that: “Each 50-gram portion of processed meat eaten daily increases the risk of colorectal cancer by 18%.”
In Australia, for example, the lifetime risk of being diagnosed with bowel cancer is 8.2%.
So people who eat 50 grams of processed meat per day would have a 9.3% lifetime risk. And people who do not consume any processed meat at all would have a 7.9% lifetime risk.
Now, the number is less impressive. To say “processed meat eaters have 1.1% more lifetime risk of getting bowel cancer” would probably not convince many people to give up their meat!
However, the important thing is that even though the number is less impressive when we calculate it in absolute terms, it does add up to other factors.
Someone who eats a plant-based diet, exercises, doesn’t smoke or drink alcohol and eats lots of fiber now is starting to put the odds in their favor and reduce their overall, absolute risk of cancer in a significant way.