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How People Actually Behave When They Know Their Genetic Risks

Should you take a DNA test? Science shows knowledge of our genome affects our behavior — and not always for the better.

Credit: Andrew Brookes/Getty Images

SServices like 23andMe make it easy to learn about the history hidden inside our genetic code. Although it is fun to learn about our ancestry and whether or not we can smell asparagus in our urine, genetic testing can raise serious questions about our health. Is it helpful to find out that we are likely to suffer from cardiovascular disease or develop Alzheimer’s in our older age?

Learning about our specific genetic health profile might help us optimize our behavior and lifestyle to minimize our risks. If we know we have a high risk of cardiovascular problems, perhaps we should hop on a treadmill more regularly and take better care of our diet. On the other hand, learning about a high risk of disease is likely to make us unnecessarily anxious, and the stress may even make our health worse.

To make an informed decision about whether to offer our saliva to genetic testing companies, it helps to know how people behave once they gain knowledge about their genetic predispositions.

One group of researchers at Stanford tested the question directly. They sequenced the DNA of 116 people to understand their risk profile in relation to physical exercise capacity, focusing specifically on a gene known as CREB1. People with a high-risk CREB1 genotype, rather than a protective CREB1 genotype, typically have poorer aerobic capacity and struggle to benefit from physical exercises. So the researchers split participants into groups according to these genotypes.

Importantly, this actual genetic risk was not the only variable of interest. The researchers were trying to understand how people’s knowledge and beliefs about their genetic risks could affect their behavior, so they introduced an additional manipulation. For each of the genotype groups, the researchers randomly told half the people in the study that they had the high-risk genotype and the other half that they had the protective genotype. Of course, this involved some temporary deception for men and women who were told they had the wrong genotype, so the researchers were careful to fully debrief everyone at the end of the study to make sure they understood the experiment objectives and the true facts behind their genes.

Here’s the first important result: The belief manipulation worked. Regardless of their true genetic profiles, people who were told they had high-risk genotypes believed they were more vulnerable to poor exercise capacity than people who were told they had protective genotypes. They also expressed more worry and less control over their physical health.

To see how those beliefs affected actual behavior, everyone in the study completed a treadmill running test, both before and after they were told about their genetic risk. This allowed researchers to measure each person’s baseline physical performance before checking how their performance changed after the introduction of specific beliefs.

The people who were told they had a protective genotype showed no change between these sessions; they had the same aerobic capacity before and after the manipulation. But the people who believed they had the high-risk genotype struggled more in the second session. In their final, most demanding minutes of the exercise test, these people hit a plateau in their physiological measures, while the men and women with protective genotype beliefs kept pushing themselves harder in both the baseline and post-belief sessions.

Consistent with these physiological measures, people in the high-risk belief group declined in their running endurance. They stopped 22 seconds earlier on the treadmill compared to their baseline performance. In contrast, people who were told they had a protective phenotype showed the same physical endurance before and after their beliefs changed.

But how did the people in the study actually feel during the exercises? The researchers took several measures of subjective experience as people ran on the treadmill. Compared to their baseline, those with the protective beliefs ran 47 seconds longer before reporting that the exercise was “hard” and 67 seconds longer before saying they felt “hot.” This is true even though they ran at the same intensity during both sessions. The people with the high-risk beliefs showed none of these advantages.

Does this apply to other genes?

To prove that these effects were more than a one-hit wonder, the researchers ran a second experiment, this time isolating a different candidate gene related to obesity known as FTO. A high-risk FTO genotype is linked with reduced satiety after eating and stronger responses in appetite-related brain areas when looking at pictures of food.

Repeating the protocol from the first experiment, the researchers used a genetic test to find people with high-risk and protective FTO genotypes and told half of each group their true genotype, while making the other half believe they had the opposite genotype. But instead of asking people to run on treadmills during behavioral testing, they simply asked them to consume a meal before and after the genotype beliefs were manipulated. The researchers then examined whether the people in the study reacted differently to their meals after their beliefs changed.

Positive expectations can shift us into a productive mindset, and negative expectations can make us pessimistic about our health, fitness, and self-control.

Once again, the belief manipulations were effective because the people who were told they carried a high-risk rather than protective genotype were more worried about their ability to control their satiety.

Despite eating exactly the same meal in both sessions, the people who believed they had a protective genotype showed greater levels of a hormone related to feeling full after their beliefs changed, in comparison to their baseline. The high-risk-belief people showed no changes. Similar to the participants from the first experiment, people’s bodily functions physically changed depending on their beliefs and expectations — and their subjective experiences fit the same pattern. People with protective beliefs reported feeling more full after eating, regardless of their true genotype.

So, what does this all mean?

For now, there is no easy answer to the question of whether you should learn about your genetic health risks. Positive expectations can shift us into a productive mindset, and negative expectations can make us pessimistic about our health, fitness, and self-control. However, at least in the context of the experiments above, these effects were measured over just a single day, primarily because the ethical implications of deceiving participants about their genotypes would have grown larger with time.

Some other studies have focused on measuring the effects of genotype transparency over the course of several months. One study genetically tested older people to learn about their risk for Alzheimer’s. In that study, rather than including any kind of deception, some people were given the choice to learn their high or low risk, while others went without knowing. Months later, the people who knew they had a high genetic risk for Alzheimer’s performed worse in memory tests and judged their memory more harshly than people who never knew about their own high-risk genotype.

However, people in this Alzheimer’s study were not randomly split into groups with different beliefs, which means other group characteristics may have explained why people who chose to look at their genetic disadvantage also had worse outcomes. This is the natural downside of removing all elements of deception from belief manipulations. So we need to wait for stronger evidence before assuming cause and effect.

The results from these studies are a fascinating extension of what we know about the placebo effect. We know that the beliefs we hold — whether they are true or not — change bodies and behavior. But unlike the traditional placebo effect, people in these studies did not need to take a fake pill to be convinced that their body was being influenced. Instead, they were simply misled about the natural state of their existing bodies. The belief that they had a particular genotype forced their behavior into a mode consistent with that genotype.

For many of the outcomes in the studies, people’s beliefs about their genotypes had a more profound impact on their behavior than the actual genotypes themselves, at least in the short term. Genes are, of course, critical in our development, and these results should not encourage us to veer toward a blank-slate hypothesis where we insist that our environment matters more than our genes. It should only reiterate the boring truth about the nature versus nurture debate, which is that both matter enormously. Nature deals us our cards, and nurture determines how we play them.

Given the current unknowns, we should remain cautious. It may be that the long-term costs and benefits of learning your genetic health profile depend on your personality. If you feel you would be highly motivated to improve yourself if you found that you had a high-risk genotype, perhaps it is a good idea for you to gain some certainty about your biological makeup. But if you are particularly anxious, perhaps you are better off not knowing at all. Each of us, as individuals who care about our personal well-being, need to use the available evidence to make our own informed decisions.

As technology becomes increasingly able to reveal deeper facts about our personal identities, we will need to consider which facts we do and do not want to know. Sometimes too much information can be counterproductive and even harmful. Maintaining the ideal balance is challenging, but it is a challenge worth fighting. Our false intuitions about statistical risk and biological determinism mean that when we see our genetic vulnerabilities, we may unconsciously act as if those vulnerabilities are already at work. But if we follow the evolving scientific evidence on how expectations affect health — if we remain conscious that human beings can be their own own worst enemy — we can at least live free of fear.

Neuroscientist writing about brains, behavior, & health. “Understand more, so that we may fear less” — Marie Curie.

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