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What is a health risk?

Being alive is a health risk. Taking action with regard to your health - such as undergoing treatment - also involves some health risk. The important questions are:

• how much risk?
• is the risk worth it?

Not taking action on your health also involves risk - but this risk is often more difficult to identify or appreciate. Partly, this is because the consequences are in the future, rather than being immediate.

People often respond best to the prospect of immediate rewards, so there is sometimes little incentive to take action now for your future health, and doing/changing nothing may be the result.

Get to grips with risk

Is the risk important?

It may be that your doctor has recommended using a medication, in the hope it will relieve a troubling condition. You are told the treatment is known to carry, let's say, a 1% (or 1 in 100) increased risk of the patient having a heart attack while using the treatment. This may seem worrying - however, a closer look at the risks may help put it into context.

It may be that for someone of your age and in your state of health you already have an estimated 2% (2 in 100) risk of heart attack in the next five years. So, in effect, by taking the medication, your risk of heart attack would move up from 2% (2 in 100, or 1 in 50) to 3% (3 in 100, or about 1 in 33).

Looking at the actual numbers can help you get the information you need to make a decision and decide whether a risk is relevant in the context of both your existing overall risk and the likely benefits of a new treatment. Also see below - Absolute versus Relative Risk - which illustrates this point further.

Swapping one risk for another

You cannot avoid risk altogether - avoiding one risk may pose another. For example, if you have high blood pressure and your doctor prescribes medication to lower it, there is a risk of side effects. But by not taking the medicine to avoid the side effects you increase the risk of a stroke, or other serious life-threatening event, due to untreated high blood pressure.

Absolute versus relative risk

"Consider your individual risk of being struck by lightning. Now let's say you (for some reason) carry around a large iron bar. This increases the relative risk of being struck by lightning by 100 or even 1000 times. But the absolute risk is still tiny because the original number was so small."

- An example of the difference between relative and absolute risk, attributed to British epidemiologist Hugh Tunstall-Pedoe.

So, how risk is presented is important. Whenever anyone is trying to explain risk, it's worth finding out what sort of risk they mean. If you hear that a medication halves or doubles your risk of this or that, it is worth finding out whether this means the absolute risk changes between a 1% and a 2% risk or between a 25% and a 50% risk - otherwise you are really not being well informed.

We all perceive risks differently

Many things affect how we perceive risks. Whether a risk is judged to be acceptable can be altered by whether the risk or outcome is:

• Immediate or delayed
• Under your control or not under your control (eg, being a driver versus being a passenger in a speeding car)
• Permanent or temporary
• A dreaded situation or one not considered dreadful
• Heightened awareness (eg, stories in the media) or less commonly known about.

So, risk is perceived differently by different people. Preconceived notions play a part. GM food and mobile phones are both commonly perceived to have a (probably) small, unquantifiable and theoretical risk of harm to human health, but no one seems to want to eat GM food and everyone wants a mobile phone.

Risk per year or lifetime risk?

The Heart Foundation estimates that the lifetime smoker will, on average, have a life that is 14 years shorter than that of a nonsmoker. As this figure is an average, this could mean anything from a one to a 30-year reduction in lifespan for regular lifetime smokers.

If you said to a smoker the chances of the average smoker dying from smoking this year are about 1 in 200, they probably wouldn't bet on a horse at those odds, so probably they wouldn't be prompted to quit smoking either.

But a letter in the 27 September 2003 edition of the British Medical Journal recounts how Richard Peto (responsible for many of the big studies on the effects of smoking) tosses a coin and slaps it on the back of his hand to illustrate to his audience the (true) 50% risk of being killed from long term tobacco smoking. "It always produces a gasp of surprise."

Unlike the first example, this describes the cumulative risk - the total of the smaller (yearly) risks.

Cumulative risk can also be made up of a number of different risk factors acting on the same person's health. So when your doctor says you should get a bit more exercise, lose some weight and drink a bit less alcohol, he is looking at the "big picture". Even moderate improvements in these areas can, over the long term, mean much better health years later.

Heart disease and diabetes are two areas where the risk factors overlap, accumulate and can "ambush" you before you realise what's happening… for more on these risks, see Heart risk - tackling your risk factors.

Also see: Know Your Numbers Heart Age Calculator

Original material provided by everybody, and reviewed 2006.