Only a minority remains mentally healthy for the rest of their lives.

Most people fall ill with a mental disorder until they reach the age of majority. Regular screening of children and adults should therefore be as natural as checking blood pressure.

Most of us know at least one person who has had a mental illness before. Although such phases of life are common, they are usually considered unusual and even shameful. However, new findings from around the world, including from our research group, suggest that the majority of people will develop a diagnosable mental disorder at some point in their lives.

It has long been known that at any given time about 20 to 25 percent of the population suffer acutely from a mental illness. They are so mentally burdened that their private lives, their performance at school or at work are impaired. Most of those affected do not receive any therapy.

As early as the mid-1990s, extensive studies in the USA suggested that almost one in two people was affected at some point in their lives. These studies included thousands of participants who were representative of the entire United States in terms of age, gender, social origin and ethnicity. However, they were retrospective surveys, i.e. they were based on the respondents’ memories of feelings and behaviors months, years, or even decades ago. But our memory is fallible, as research shows: When people are asked about their mental condition, they often give changing or contradictory information. It is therefore questionable how reliable such retrospective findings are. Moreover, every third person who is invited to such studies refuses to participate. And as further surveys suggest, on average these people who refuse to respond tend to have poorer mental health.

Only about every sixth person is permanently mentally healthy.

Another approach is therefore pursued by a current study by one of us (Schaefer), which appeared this year in the “Journal of Abnormal Psychology” (the very name suggests an outdated understanding of illness). Instead of asking the subjects to think back many years, we followed a generation of New Zealanders from the same city from birth to middle age. Every few years, we looked for clues to a mental illness and found that in such regular screenings with research-based instruments, the proportion of those who suffer from a mental disorder, at least for a short time, rises to more than 80 percent. In our cohort, only 17 percent were spared until middle age. Because our team could not be sure that the participants had remained healthy in the years between the screenings, the proportion could be even lower.

“And another conclusion suggests itself: research should examine closely those people who do not get psychologically ill even once in their lives.”

In other words, the study shows that most people are likely to develop a mental disorder one day. It is more likely than diabetes, heart disease or cancer. Similar cohort studies in Switzerland and the USA have confirmed our data.

Once ill, always ill? Not true!

A common assumption is that once you become mentally ill, you will stay mentally ill for the rest of your life. According to new findings, however, this does not apply to the most common psychological complaints. “Mental illnesses are often short-lived or not so serious,” says epidemiologist John Horwood, director of a large longitudinal study in Christchurch, New Zealand. Almost 85 percent of his test subjects also suffered from a mental disorder at least once up to the age of six.

This finding could be a useful message. As social psychologist Jason Siegel says, people are more compassionate and helpful when they believe that the health problems of a friend or colleague are passing. And that’s exactly what people need: support. Because even short-term complaints can cause devastating damage in a person’s life. To be diagnosed as mentally ill, Horwood says, you have to meet very strict criteria. “The disorder must affect life considerably.

Some people may think that such findings pathologize normal human experiences. But many stakeholders of affected people contradict this view. “The numbers don’t surprise me at all,” says Paul Gionfriddo, president of Mental Health America, a national advocacy group for patients. The organization considers mental illness to be widespread, but not necessarily persistent. Three years ago, Mental Health America launched a web-based tool that allows people to independently check whether they have a mental illness and may need treatment. Since then, it has been used 1.5 million times and 3000 screenings are added every day.

High morbidity rates also have consequences for the way we investigate and treat diseases, according to Gionfriddo, a patient representative. His son had schizophrenia when he was a child and lived on the streets and ended up in prison. “Society would benefit enormously from a general screening of mental health,” says Gionfriddo.

A US prevention task force is currently recommending such screening for every child 11 years and older. And yet it is far from being routine. “It should also be common practice for adults to have their blood pressure measured,” he adds.

A robust soul can already be seen in five-year-olds

And there is another conclusion that suggests itself: research should examine those people who do not suffer from mental illness even once in their lives. Their mental constitution obviously corresponds to the physical constitution of healthy 100-year-olds: it defies all adversities. Studying her robust psyche could provide useful insights and thus help many other people.

Who are these extraordinary people? In our New Zealand cohort we found two special characteristics: First, their relatives were also rarely affected by a mental disorder. Secondly, we found beneficial personality traits in them: At the age of five, they apparently experienced less negative feelings, coped better with their peers, and had greater self-control. It should be noted, however, that in childhood they were neither richer nor smarter or physically healthier than their peers.

The most important finding, however, is that mental illnesses are almost universal. Society should therefore consider these complaints as well as broken bones, kidney stones or colds: as normal ups and downs of human life. This would enable us to provide the necessary resources for screening, treatment and prevention of mental illness. And it could also help to be more lenient with ourselves or with loved ones in difficult times.