Can You Walk off the Risk of Breast Cancer?

One of this week’s health stories is typical of how rather unexciting research can reach the headlines by virtue of its association with a condition like breast cancer, but it also serves as a good example of two of the most common sources of sloppy reporting that plague health stories – which makes me think it a subject worthy of a blog.

The research relates to the possible effect of exercise on the risk of developing breast cancer, and the headline is Walking ‘cuts breast cancer risk’. If true, this is hardly an earth-shattering discovery. Perhaps it will add in some small way to our understanding of the mechanisms involved in the development of cancer, but this is for the journals to worry about. When it appears in mainstream media, the point is surely whether it means anything to an individual concerned about her breast cancer risk – in other words, if you want to reduce your risk of developing breast cancer, should you take up walking? Unfortunately, the way the results are reported makes it very difficult to answer this question.

 

Problem 1: associations are not the same as cause and effect

The first problem is that the study has made an observation, which has been presented as a cause. The researchers did quite a simple thing: they arranged for a group of over 73 000 post-menopausal women to complete a questionnaire at intervals over a 17 year period from 1992 to 2009, asking questions about how many hours walking the women did, and any diagnosis of breast cancer. They found that those who walked for 7 or more hours per week were less likely to have been diagnosed with breast cancer than those who walked for 3 hours or less. This does not mean that the walking caused the reduction in risk, however. It may well have done, but it could have been some other factor. There could have been a different cause that was linked to both breast cancer risk and the amount women walk. For instance, walking less could be linked to obesity, which could explain the extra breast cancer risk.

The researchers were aware of this problem, and tried to exclude some factors – for instance, it was not due to those who developed breast cancer being more overweight than those who did not – but they can never exclude all of the possible confounding influences. For instance, it may be that those who walked less were more likely to have other health problems, and the increased risk of breast cancer was in some way linked to this.

In my experience, observational health studies are very frequently reported as cause and effect. I can understand why – Walking ‘cuts breast cancer risk’ Has more of a ring to it than Walking is associated with a reduced risk of breast cancer. The problem is that the more catchy headline is misleading, and it is left to the reader to spot the error.

Problem 2: what do we mean by a reduction in risk?

The second pitfall when it comes to knowing what to make of a study like this is more serious – and more troubling, because the fault lies not with mainstream journalists trying to enhance their stories, but researchers and journal editors being guilty of the same. The problem is this: as is so often the case, the results have been presented in terms of a reduction in relative rather than absolute risk.

The trial demonstrated a 14% Relative Risk Reduction (RRR) – but is that a 14% reduction of a big number or a small number? If the Dragons in Dragons’ Den are offered a 14% share in company profit, they are very quick to ask how big that profit will be before they part with their money. The same should apply to us before we invest our energies in a health intervention. If the Dragons want to know the absolute amount of money they can expect to receive then we should expect to know the Absolute Risk Reduction (ARR) of any intervention.

The problem is that ARRs are always a lot smaller than RRRs, and so they make research look far less impressive, and researchers are reluctant to give them the attention they deserve. From the BBC article it is impossible to find the ARR, and so you have to go to the original research – and even here only the abstract is available without paying a fee and so you have to work the numbers out for yourself. It turns out that the risk of developing breast cancer over the 17 years of the study was 6.4 percent, making a 14% RRR equate to a 0.9% ARR.

Let us assume for the moment that the reduction in risk really is due to walking. Then if you are a woman after the menopause, and you walk for 7 hours a week rather than 3, then over a 17 year period you would reduce your risk of getting breast cancer by 0.9%. Put another way, if 1000 women walked the extra 4 hours a week for 17 years that would be 3 560 000 hours of walking to save 9 cases of breast cancer, or 393 000 hours of walking per case. At 3 miles per hour, it’s the equivalent of walking more than 47 times round the world! Now I do know that this statistic is probably as meaningless as being given a 14% relative risk reduction – but it was fun to work out!

That’s not to say that walking is a bad idea – there are clearly very good reasons for walking more. However, whatever the associated health benefits might be, the two most compelling reasons to walk will always be these: it’s a very useful way of getting from A to B, and most people find they rather enjoy it!

Will Exercise Help Your Depression? Only You Can tell

The long-held belief that exercise can be beneficial in treating depression was brought into question last week by a study, published in the BMJ and widely reported in the news, which reported that exercise did not improve recovery in patients suffering from depression.

Exercise
Exercise can take many forms, but will it help depression?
Image courtesy of freedigitalphotos.net

As you can imagine, the study has prompted much debate. Can such a definite statement be made about so complex and varied a condition as depression? (probably not); how do you define exercise? (your guess is as good as mine); is that really what the study showed? (not really, it just showed that patients encouraged to undertake a programme of exercise got better at the same rate as those who did not). Interesting and erudite as these discussions might be, they are not really relevant if you have depression and want to know whether or not to get your trainers on – because you don’t want to know if exercise will treat depression, you want to know if it will help withyour depression. Thankfully there is another clinical trial you can refer to – the ultimate clinical trial where n=1 – that means there is only one patient (you) trying one treatment and seeing if it works.

We do a lot of n=1 trials in medicine. Every time we try a cream for a rash, a medicine for indigestion or an antibiotic for tonsillitis we are essentially conducting an experiment: Here’s a symptom, there’s a treatment, see if it helps. If it doesn’t, try something else. It’s not great science, but it is good medicine.

Of course, an n=1 trial won’t work for everything in medicine. Firstly, you need to be sure that the treatment you are about to try doesn’t carry a significant risk (which is why frontal lobotomy as a cure for depression has somewhat gone out of fashion), and then you need to be able to know if it has worked, and in a reasonable timescale. For this second reason, a trial of treatment is not much help when it comes to deciding many of the big questions in medicine – like whether or not to take a statin for cholesterol, or to have your PSA measured to try to detect prostate cancer – for these dilemmas there is no escaping the need for large-scale clinical trials to help guide us. A statin is not going to make you feel better, so how would you know it was working? Even if it lowers your cholesterol, how do you know that this will do something that actually matters to you – like stopping you having a heart attack? There’s no value in a ‘try it and see’ approach here.

Exercise in depression, however, is ideal for an n=1 trial. Exercise is clearly a safe treatment to try – more than that, we know it has many health benefits beyond any help it might be for depression. What is more, there is good reason to think it might help lift mood – whether it is just the benefit of feeling fit, effects on serotonin levels or the magic of endorphins it seems worth looking into. What is more, those who testify to its benefits report that they actually feelbetter soon after exercise – no need for a 2-6 week trial like there is for antidepressants. Of course, you may have to try it a few times to get a feel for it. You might overdo it one day and feel worse, or find one form of exercise works better for you than another, but the message is clear – if you are going to benefit, you will feel the benefit of your experiment sooner rather than later.

So what should you do if you have a negative trial – if you give exercise a go and feel as flat as ever, or maybe even worse? Well there is still a more general principle that will work for everyone, and it is this: When you are depressed there will be some things that, when you do them, help you to feel a little bit better. Whether it is exercise, gardening, music, art stroking the cat or just getting up on time in the morning doesn’t matter – whatever it is, you’ll feel better if you do it, so try to do it more!