Of all the cultural beliefs about health and illness that saturate the developed world, there is none so pervasive and deeply held as the idea that you can “battle” an illness by sheer force of will.

We admire people like AFL great Jim Stynes who show a brave and positive face to the public when confronted with a diagnosis of cancer, and somehow expect that a positive and determined mindset will help “overcome” the disease.

The underlying assumption here is that the mind and body are separate, a philosophical stance known as dualism.

In contrast, the scientific viewpoint is that the mind is caused by the brain. And all the neuroscientific data points this way.

So what, you may say. Even if the mind is caused by the brain, I can still consciously control my thoughts, and therefore I can influence things that go on in my body. This is quite true.

The next question, then, is whether there is evidence that optimism, positive thinking or learning to control your thoughts in some way will be enough to have a significant influence on any disease process.

It’s important to note that we’re not talking about quality of life. We’re interested in whether the actual course of a disease can be changed by purely mental effort.

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It’s common sense (and supported by mountains of positive studies) that sick people’s quality of life can be improved by having a positive outlook.

The consensus is that optimistic people turn up for their treatments more regularly and are more likely to find resourceful ways to get as much as they can out of their life with chronic illness.

Interestingly, pessimism may be more predictive of a bad outcome than optimism is of a good one.

What does the evidence say?

The most comprehensive summary of the evidence on the subject of optimism and health is this 2010 analysis of 83 studies . Most of the studies take a cohort of subjects, score them by questionnaire to rate their levels of optimism, then sit back and watch what happens.

There are no control groups and no intervention to assess – the researchers just trawl the data for a correlation. If links are found, which isn’t always the case, a press release is issued and everyone marvels at how amazing the mind-body connection is.

Even if you find a robust and reproducible correlation, it doesn’t automatically follow that the link is causal. This is especially true if the study was not specifically set up to show the exact link you are looking for, with all bias and potential distractions removed.

I couldn’t find any studies that were set up to look at the effect of becoming more optimistic, or switching from pessimism to optimism, on a person’s disease.

But at least there’s no harm in being positive, right?

There’s not, but it’s possible that being blindly and unrelentingly positive can be a burden to disease sufferers.

US researcher James Coyne makes this point in his 2010 paper critiquing the positive psychology movement in cancer care. Coyne notes that enforcing a cultural expectation of positivity leaves many cancer patients scared that they’re reducing their chance of survival every time they feel scared, depressed or angry about their disease.

The paper quotes Dutch Olympian Maarten Van der Weijden, who rejected being identified with Lance Armstrong’s approach of “fighting” cancer:

What he basically says is that it is your own fault when you don’t make it… You always hear those stories that you have to think positively, that you have to fight to survive. This can be a great burden for patients.

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Cancer patients should be reassured that their disease was not caused by personality or emotional factors. Such a callous and false conclusion follows logically from a serious acceptance of the myth. It also would follow that cancer, multiple sclerosis, stroke or any other serious disease could be curable by addressing the emotional issues that supposedly underlie it.

So if there’s little evidence that just being an optimistic person is good for your health, there’s even less evidence that forcing yourself to use positive thinking can beat your disease. Positive psychology interventions have only really been studied in mental health diseases such as depression and there seems to be no attempt to use thought to cure disease.

If faced with a serious illness, you’re likely to have a better quality of life if you have good social supports and avoid giving in to complete pessimism. Nobody can tell you the perfect formula to deal with the impact of a serious diagnosis.

But don’t believe those who tell you your illness is your fault somehow, or that you wouldn’t have it if you’d somehow been a better person.

You don’t need to feel that you should be completely positive 100% of the time, because not only does that not happen, it’s not healthy either. Coping the best way you know how to is all you should be aiming to do.