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---
  layout: post
  title: Hazard and risk
  author: Joe Schwarcz
  source: McGill Blogs
---
  HYPERLINK "http://blogs.mcgill.ca/oss/2015/11/26/hazard-and-risk/" 
Hazard and risk 

  If you watched the news, read newspapers or surfed the web recently
you will have been inundated with pictures of bacon and headlines
describing it as carcinogenic. That’s because the International Agency
for Research on Cancer (IARC) classified processed meats as being
carcinogenic, placing them in the same category as tobacco smoke,
asbestos, oral contraceptives, alcohol, sunshine, X-rays, polluted air,
and inhaled sand. However, it is critical to understand that the
classification is based on hazard as opposed to risk. Hazard can be
defined as a potential source of harm or adverse health effect. Risk is
the likelihood that exposure to a hazard causes harm or some adverse
effect. If a substance is placed in IARC’s Group 1, it means that
there is strong evidence that the substance can cause cancer, but it
says nothing about how likely it is to do so. That likelihood depends on
several factors including innate carcinogenicity, extent of exposure and
personal liability. Ultraviolet light, a component of sunlight, is a
good example to illustrate the difference between hazard and risk

Light can be thought of as being composed of packets of energy called
photons. When a photon impacts a molecule of DNA it can damage it,
triggering an irregular multiplication of cells, in other words, cancer.
X-rays are also made up of photons, but these are more energetic than
the photons of ultraviolet light so they are more likely to damage DNA.
Although both sunlight and X-rays are in Group 1, X-rays are clearly
more capable of triggering cancer than sunlight. But exposure matters. A
single chest X-ray is not a problem but repeated baking in the sun is.
More photons of lower energy can have a greater effect than fewer
photons of greater energy. Then there is individual liability. A person
with dark skin is less at risk for developing cancer than someone with
pale skin even at the same ultraviolet light exposure.

Inhaled sand is also listed in Group 1. That’s because studies have
shown that workers engaged in occupations that can result in inhaling
sand show a significantly increased risk of cancer. But this doesn’t
mean that going to the beach and frolicking in the sand is a risky
business. Tobacco smoke is also in Group 1because there is no doubt that
it causes lung cancer. In fact about ninety percent of all lung cancer
cases can be attributed to smoking. Alcohol is also in this category
because it is known to increase the risk of oral cancers as well as
breast cancer, yet nobody worries about drinking a glass of wine.
Listing processed meat in IARC’s Group 1 just says that like alcohol,
like tobacco, like sunshine, and some 180 other chemicals, mixtures and
exposure circumstances, it is capable of causing cancer. It does not
mean that if you have a bacon lettuce and tomato sandwich you are
putting yourself at risk.

Let’s clarify what is meant by processed meat. Grinding meat into
hamburger does not result in processed meat. But smoking, fermenting or
adding chemicals such as salt or nitrites to either extend the
product’s shelf life or change its taste does. We’re talking about
bacon, sausages, hot dogs, salami, corned beef, beef jerky and ham as
well as canned meat and often meat-based sauces.

The evidence that these tasty morsels are linked to cancer comes from
observational studies, which of course do not prove cause and effect.
But they are quite consistent in demonstrating that populations that
consume lots of processed meats have higher cancer rates, particularly
colorectal cancer, even when corrections are made for smoking, other
foods eaten and activity levels. Furthermore, there are theoretical and
experimental foundations for declaring some components found in
processed meat, like polycyclic aromatics, heterocyclic amines,
nitrites, insulin-like growth factor and heme-iron, carcinogenic.

The evidence is certainly not ironclad, but science rarely is. It comes
down to making educated guesses and evaluating the downside of such
guesses. There is no significant downside to limiting processed meat,
especially if it is replaced by plant products.But the significant
question to ask is how much can we reduce our risk of colorectal cancer
by robbing our taste buds of the taste of bacon and such? The risk of
this cancer in the general population is roughly six in a hundred. After
poring through some 800 peer-reviewed publications, IARC estimates that
eating 50 grams of processed meat every day over a lifetime increases
risk by about 18%. In other words, if a hundred people follow such a
regimen over a lifetime, there will be seven cases of colorectal cancer
instead of six. So for an individual, the chance of getting colon cancer
because of eating processed meats is about 1 in 100. That is a very
small risk, but because there may well be millions of people following
such a diet, the impact on the population can be significant, in
IARC’s estimate, about 34,000 cases a year.

What do we do with this information? A one in a hundred chance is not
insignificant and it makes sense to try to reduce it. That means
consuming less than 50 grams of processed meat a day on average. To do
that we need to keep some numbers in mind. Two to three strips of bacon
add up to 50 grams, as do two slices of ham, 4 slices of salami or one
hot dog. Remember though that we are talking averages here. Certainly a
couple of hot dogs, a salami sandwich and a couple of bacon and egg
breakfasts a week is not a great risk. But if you have a smoked meat
sandwich, well, you have used up your weekly allotment. But remember
that all these numbers are estimates, basically educated guesses, and
are not based on hard evidence.

Joe Schwarcz – Nov 26th/2015