One Friday morning at my practice, I meet Jake*, a 42-year-old computer engineer with an unexpected favour to ask.

I am a little intrigued to know why he is sitting opposite me. That’s because Jake is normally well and an infrequent attender – a quick look at his medical record shows me that he last attended in 2013 for ‘tennis elbow’. He has no other past medical history of note. He is a non-smoker and drinks little alcohol.

Jake starts off apologetically: if possible, could he have a blood test to check his PSA level? PSA or prostate specific antigen is a protein produced exclusively by the prostate gland. High PSA levels can sometimes be used as a marker for prostate cancer but there can be other non-cancerous reasons for PSA levels to be high, such as a urinary tract infection and inflammation of the prostate.

I wait for Jake to elaborate. Instead he reaches into his jacket and produces a computer printout – it is an essay by the actor Ben Stiller on ‘The prostate cancer test that saved my life’.

Jake has no reason to take this test – but Ben Stiller’s story seemed to touch a nerve with him

Jake has no reason to take this test – but Stiller’s story seemed to touch a nerve with him, and he is now worried. Detailed questioning reveals that he has no family history of prostate cancer and no urinary symptoms at all. So, I decline – but explain that the test is only useful to diagnose men if they are experiencing urinary problems or their prostate cancer treatment is being monitored through serial testing of PSA levels. Two thirds of men taking the test will have a positive result despite there being no cancer (called a ‘false positive’) – with the needless worry and investigations that this will entail. Conversely 15% of men will have prostate cancer with very low PSA values – in other words show a ‘false negative’ result.

As a family doctor working in the UK’s National Health Service, I often see patients’ health beliefs being influenced by the world around them, whether it is through newspapers, social media, television or experiences of those closest to them. And I find requests like Jake’s – based on a celebrity endorsement – increasingly common.

Indeed, researchers have been exploring in recent years how the health choices of the people we see in TV, movies and public life can have a significant effect on people’s decisions, worries and behaviour. This pattern has been coined as the “Angelina Jolie effect”, after what happened when Jolie wrote an influential article in the New York Times in 2013. In an emotive piece she talked of inheriting a ‘faulty gene’ which gave her an 87% chance of breast and 50% chance of ovarian cancer. She announced that she had undergone a preventative double mastectomy and endorsed gene testing in other women.

In the 15 days that followed the editorial publication, there was a stark rise of 64% in US women undergoing the test for BRCA (Breast Cancer 1 and 2) genes. However there was no overall change in mastectomy rates in women – in fact there was a fall in mastectomies in those tested for BRCA genes. It seems that simply being aware of the Angelina Jolie story was not linked to women being more informed of their choices in many cases this led to unnecessary testing and worry, whilst those at genuine risk were not targeted.

On another occasion at my practice, I speak on the telephone to a mother worried about her 12-year-old who is being selective with her eating, by excluding both dairy and gluten from her meals. In this case, the girl’s peers, coupled with celebrity endorsements, have had a more concerning kind of influence.

Our tests have excluded coeliac disease and any intolerance to food. There is no reason, except that a few of the girl’s friends are following similar diets. I arrange with Mum to meet them both the following week. We are both worried.

It’s not uncommon to see patients following gluten-free diets in the absence of a medical diagnosis. With endorsements from Gwyneth Paltrow, Novak Djokovic and Victoria Beckham, the gluten-free brigade has an impressive following.

It’s not uncommon to see patients following gluten-free diets in the absence of a medical diagnosis

But how prevalent is the intolerance? Around 1% of people have coeliac disease but only around 0.25% are diagnosed, so some of the undiagnosed may be adhering to gluten-free diets to manage their symptoms. Still, the rise in the gluten-free industry has led far more people to believe that they have coeliac disease when they do not. The vast majority of gluten-free products are being purchased by those not suffering from the condition. This is particularly true in young women, who are willing to pay substantially more for these products.

For those without coeliac disease or non-coeliac gluten/wheat sensitivity (NCGS), avoiding gluten may act as a placebo alone. It could even pose a health risk, such as in children or those with eating disorders, who could use it as an excuse to eliminate foods from their diet.

Not all celebrity endorsements are questionable, however. There have been some thoughtful and collaborative campaigns, which have aimed to promote healthy behaviours. For instance, Princes William and Harry and the Duchess of Cambridge are mental health ambassadors for the Heads Together campaign and have helped to keep children’s mental health at the forefront.

Rihanna and Prince Harry also helped raised awareness of HIV testing when they took self-tests recently in Barbados. Previous HIV testing by Prince Harry in a Facebook video resulted in a massive surge in uptake of HIV testing. In this case channelling celebrities appropriately was a cost-effective way of reaching a large audience quickly and effectively.

But in general, celebrity health endorsements must be taken with a healthy dose of scepticism. They can sometimes help, but there are often downsides.

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Zara Aziz is a doctor based in Bristol, UK. Twitter: @zara_aziz

*Names and some details have been changed

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