DNA tests can come with a placebo effect

Being aware of a genetic risk can cause a 'placebo effect', a recent study has found.

Researchers at Stanford University, California, found that merely receiving information about your genetic risk profile can alter your outcome on exercise endurance and food consumption tests, regardless of whether or not you are at genetic risk. 

'Receiving genetic information doesn't just make you more informed,' lead author Dr Alia Crum said. 'What this study shows is that it can also have a physiological impact on your body in a way that actually changes your overall risk profile.'

Participants were recruited for what they were told was a 'personalised medicine study'. The researchers took DNA samples from the group and later the participants were given either an exercise test or told to eat a meal. 

The cohort then received randomly assigned 'genetic information' regarding their obesity risk and exercise capacity that may or may not have been true. The tests were then repeated. Those who were told they had a gene making them less prone to obesity produced two and a half times the amount of hormone corresponding to fullness after the same meal, whereas people who were told they had a lower capacity for exercise performed much worse on a treadmill test. 

The authors of the study said that the results didn't necessarily suggest that DNA testing is good or bad. Instead they highlighted the importance of how that information is delivered by doctors or genetic testing companies. 

'The take-home message here is that the mindset that you put people in when you deliver genetic risk information is not irrelevant,' Dr Crum said. 'The mindset of being genetically at risk or protected can alter how we feel, what we do and – as this study shows – how our bodies respond.'

The researchers are now interested in methods of explaining genetic risk that reduce the effects they report in this study.

'How can you deliver genetic information in a way that has the beneficial effects in terms of motivating people to change their behaviour but that doesn't provoke a negative effect on physiology, emotions and motivation? That's where I think a lot of really good work can be done,' Crum said.

The research was published in Nature Human Behaviour.