IN THE 1980s, A young psychology professor in California was looking for a new way to approach an old riddle: why some people enjoy good health while others fall ill and die prematurely. Beyond the physical circumstances that set one life apart from another, wouldn’t mental factors play a part as well? Centuries of speculation had swirled around that question: pessimism, hypercompetitiveness, lack of religious devotion, being unsociable—all of those traits had at one time or another been thought to make people less well. But Howard Friedman, now distinguished professor of psychology at the University of California, Riverside, wanted good data—a smoking gun.

Friedman found a wealth of that data in Stanford University archives that had been amassed about 1,500 people, all born between 1900 and 1925. They had been followed from childhood through their adult years as part of the Terman Study, which examined leadership potential in intellectually gifted kids. In his landmark 1993 paper, Friedman reported that children whose parents and teachers rated them, at age 10, as particularly conscientious—well organized, persistent, responsible—were 30% less likely to die during any particular year in their adult lives than their less conscientious peers. In a less positive finding, the most cheerful and optimistic kids—who may have had a more laissez-faire attitude about their lives—were about 6% more likely to die.

“Friedman put personality and health research on the map with that study,” says Benjamin Chapman, associate professor of psychiatry and public health at the University of Rochester Medical Center. The research spurred interest in the connection between personality traits, disease and mortality, he says, and helped launch a new wave of investigation.

Recent work has taken these ideas in striking new directions. One study tied hostility in older women to a significantly higher risk of developing diabetes. In Europe, one broad measurement of personality known as Type D—which lumps together those more likely to experience social inhibition, irritability, anger and fear—is now considered so robust a risk factor for cardiovascular disease that it is included in the European Cardiovascular Prevention Guidelines.

Chapman’s own latest study, published last year in JAMA Psychiatry, brings this thinking to one of the most pressing issues in neurology: the origins of Alzheimer’s disease. His work demonstrates that a personality type in adolescence could predict, with impressive consistency, the people who would develop dementia more than 50 years later.

“The evidence that personality contributes to disease is consistent and powerful,” says Mark Blais, director of the Psychological Evaluation and Research Laboratory at Massachusetts General Hospital. “Personality influences our habits, the friends we make, the careers we choose, how far we go in school, our lifestyle—and all of that has health consequences, both positive and negative.”

Personality traits can also have more direct, physiological effects on health. Excessive, chronic worry, for instance, can increase the production of stress-related hormones and chronic inflammation, which in turn can lead to diseases of the heart or immune system. “Personality is statistically as important as blood pressure, obesity or cholesterol in predicting disease risk,” Friedman says.

Researchers envision a future in which doctors might give patients a quick personality survey as part of a medical exam and use the results to modify a treatment strategy. Studies have shown, for example, that personality predicts how likely people are to adhere to a treatment regimen, how well they cope with a diagnosis, how quickly they recover from serious illness and how willing they are to make changes to benefit their health.

Future research may also determine whether there are effective interventions to help people tweak their own settings—to alter damaging personality traits or to pump up those that are beneficial. The trick may lie in starting early, when personality is most malleable. “We can teach adolescents and college students the skills to improve self-control,” says Brent Roberts, a professor of psychology at the University of Illinois, “which is a key factor to avoid some of the health problems they’ll suffer later in life.”


THE TYPE A PERSONALITY was the first notable modern foray into linking disposition with disease. The term was coined by two cardiologists in the 1950s to describe common traits of their patients who had had heart attacks. These patients were perfectionists who were also super-competitive, impatient and wanted to achieve at all costs. People with relaxed, easygoing personalities—Type B—had a lower risk.

The research drew critics and the approach failed to catch on, in part because many found the divide into only two types of people crude and rigid. The second half of the twentieth century saw a number of attempts to create a more flexible system of personality factors, one that could be used across studies and diseases. By the 1990s, this had coalesced into the Big Five, a collection of widely observed traits. The Big Five consisted of conscientiousness, neuroticism, openness, extraversion and agreeableness. Each of those qualities existed on a spectrum from high to low. “Before the Big Five, the research on personality and health was a mess,” says Robert Wilson, professor of neurological sciences at Rush University in Chicago. “The Big Five imposed a common language.”

A person can be measured on any of these traits by how far from the average they score. The units are standard deviations, and most people fall within two standard deviations of the average for any personality trait. With this measurement in place, researchers could begin to explore correlations in finer detail. A 2017 study at Northwestern University Feinberg School of Medicine in Chicago, for instance, showed that subjects who were high in conscientiousness, extraversion and agreeableness had a lower risk of mortality, with conscientiousness as the most influential trait. And those who were high in neuroticism were more likely to die prematurely.

More precisely, one standard deviation in neuroticism increased the risk of an early death by 5%. The highest scores for neuroticism—falling, say, four standard deviations above the average—increased the risk to 20%.

Those broad outlines of those findings—that conscientiousness and neuroticism have a profound impact on health—appear in study after study. Count yourself lucky if you rank high in conscientiousness; that is, you are goal-oriented, delay gratification, follow rules, are organized and have good impulse control. Highly conscientious people tend to go to college, achieve career success, and have more stable marital and social connections. All of these correlate strongly with good health, and the group’s being more likely to achieve above-average socioeconomic status alone reduces the risk of developing 18 diseases or health conditions, according to new research from Finland. The most conscientious people also tend to take better care of their health and better cope with stress.

Contrast them with people who rank high in neuroticism, making them prone to anger, frustration, jealousy, depression and anxiety. High neuroticism and low conscientiousness are associated with health-damaging behaviors that include overeating, smoking and a lack of exercise. The negative emotions of neuroticism may contribute to chronic stress, which in turn may help spur physical harm in the form of excessive levels of triglycerides, cortisol and inflammatory C-reactive protein. The cards are indeed stacked against them.

RUSH UNIVERSITY BEGAN ITS Religious Orders Study in 1993. Its object was to look at aging and the brain by closely following the lives of 1,100 Catholic priests, nuns and brothers. From the outset, the study was designed to look at the role played by personality traits. “We were taking a chance, hypothesizing that personality and its influence on thinking and behavior might predict cognitive decline and dementia,” says study researcher Wilson.

It had already been observed that Alzheimer’s disease tends to bring personality changes—toward greater neuroticism and less conscientiousness—and that those shifts sometimes come years before the usual signs of dementia. The big question for Wilson was the order of events: whether people who display these traits are at higher risk for Alzheimer’s or whether their increasing neuroticism and declining conscientiousness might be symptoms of the disease.

During their lifetimes, the volunteers have regular exams of cognition and personality assessments. The study has found that those who ranked highest in neuroticism at older ages had a threefold higher risk of both developing Alzheimer’s disease and experiencing more rapid cognitive decline than those who scored lowest. At the other end of the scale, participants who scored high on conscientiousness had an 89% reduction in risk of Alzheimer’s disease compared with those who had the lowest scores.

Researchers then autopsied the brains of deceased study participants to look for physical changes. That’s where the shock came. Most of the brains, whether or not the person had dementia, showed surprisingly similar signs. Almost three of four participants who died in their eighties and nineties had the same amyloid-beta plaques and tau protein tangles that are hallmarks of Alzheimer’s disease, regardless of whether they had experienced cognitive problems.

“It’s very common in old age to have these kinds of dementia-related pathologies—the plaques and tangles—and those pathologies do affect cognitive function,” Wilson says. “But the pathologies explain only about half of who gets Alzheimer’s disease. There are other factors at play, and we think personality-driven behaviors and lifestyle account for a very meaningful 15% to 20% of the risk.”

But how does that personality-driven part of the risk work? Wilson is looking into how neuroticism seems to affect memory and thinking in old age. He believes that chronic psychological distress may cause as-yet unidentified structural and neurochemical changes in brain regions that regulate stress-related behavior and memory—a distinct novel mechanism. The brains of those in the study who had ranked high in conscientiousness, on the other hand, showed better functional and structural characteristics in the frontal lobe.

“We have no evidence yet that personality causes the underlying pathologies of dementia,” Wilson says. “We think instead that personality affects your ability to tolerate and be less vulnerable to the dementia-related changes that normally occur in old age,” helping your memory and cognition remain intact, he says. Data taken from a second longitudinal study begun in 1997, Rush’s Memory and Aging Project, involves a more diverse group of subjects from all walks of life but has yielded results similar to those from the Religious Orders Study.

A new study from the University of Geneva in Switzerland also suggests that personality can affect the structure of areas of the brain related to memory. The 65 elderly study participants underwent functional and structural brain imaging for almost five years. The researchers found that people who scored low in agreeableness (who were unpleasant, not afraid of conflict, anti-conformists) and high in openness (curiosity, desire to learn, interest in the world) had distinct brain features. They showed less lost volume in the hippocampus, temporal lobe and other regions that tend to deteriorate during normal aging and especially after the onset of Alzheimer’s disease.

Although being a highly agreeable person—cooperative, wishing to please others, eager to avoid conflict—is generally considered a positive personality trait, it might not hold a continued value for brain health. “In older age, agreeableness may have a deleterious effect on brain integrity when the need for social adaptation is less imperative,” says study leader and psychiatrist Panteleimon Giannakopoulos, professor and department head of the Geneva University Hospitals of Psychiatry, whose findings were published in Neurobiology of Aging. Other studies have shown that high agreeableness in older people tends to be associated with less effective executive performance and other cognitive functions, Giannakopoulos says.

Additional compelling evidence that personality is a risk factor for Alzheimer’s disease comes from another recent study, which links personality in the teenage years to the development of dementia 50 years later. Chapman, from the University of Rochester Medical Center, analyzed the personality profiles of 82,000 people who underwent personality tests in 1960 as part of Project Talent, a national study of U.S. teenagers. He then scoured Medicare records of Project Talent participants when they were about 70, searching for those who had received a dementia diagnosis.

The personality tests for Project Talent had been administered before the advent of the Big Five, but children who had shown higher levels of vigor (roughly corresponding to the extraversion category on the Big Five), calm (low neuroticism) and maturity (high conscientiousness) had a lower risk of dementia, and teens who scored at the other end of the scale for those traits—low extraversion, high neuroticism and low conscientiousness—were more likely to develop dementia.

“The kids who were bursting with energy and said that their lives were full of fast-paced activities probably liked to exercise during adulthood and may have felt they had purpose in life and more social engagement,” Chapman says. Vigor had a protective effect regardless of whether the teens came from rich or poor families.

Chapman is now looking at specific causes of death of Project Talent participants. In general, those who as children scored high in vigor, calm, maturity and social sensitivity had the lowest rates of premature deaths. Not so for the teens who were most impulsive. Chapman wonders whether he’ll find that many of the latter group have deaths related to overeating, drinking and smoking.


IF MOUNTING EVIDENCE SHOWS that personality affects health, that leads to another question: Are personality traits innate or can they be modified? Also, can interventions by physicians nudge patients toward the healthier outcomes of “better” personality traits?

Researchers long believed that personality is immutable, but that view has changed. “We know now that personality develops until about age 35,” says MGH’s Blais, who notes that upbringing and early life experiences play a big role in shaping personality. “But after that point, life-changing events—positive or negative—and even aging itself can alter personality traits. We know that, even after personality has stabilized, some traits can be reduced if they are extreme or increased if they are too low.”

Roberts, at the University of Illinois, looked at some of the ways that this might happen. In a study published in 2017, he examined the results of 207 clinical trials in which therapists were experimenting with some new type of therapy—a variation on standard cognitive behavioral therapy, for example. The investigators in those studies measured personality traits of the participants before and after the intervention, in addition to the behaviors they were most interested in changing, such as depression, anxiety, substance abuse or being overweight. “The studies showed without a doubt that personality can change, and much faster than we thought, especially regarding the trait of neuroticism,” Roberts says.

“Training programs in which participants learn some type of life skill appear to be especially effective in changing personality traits,” he says. “For example, a mindfulness intervention was associated with changing conscientiousness, agreeableness, empathy and emotional stability among medical residents.”

On average, the six- to eight-week psychological interventions in these studies changed personality by about half as much as would normally happen between ages 20 and 60, Roberts says. “That is a remarkable amount of change—half a life’s worth of change in a few weeks,” Roberts says.

In a similar vein, an ongoing study is exploring whether psychological interventions for heart disease patients might be helpful. MGH psychiatrists Jeffery Huffman and Christopher Celano are studying whether positive psychology exercises can enhance happiness, gratitude and optimism in patients with heart disease or diabetes—and, as a result, promote well-being and better health behaviors and cardiac outcomes. “Basically, they’re treating neuroticism without identifying it as such, and we are getting promising results altering behaviors,” says Nicholas Kontos, a psychiatrist at MGH.

It will be fascinating if clinicians can bring personality research into the clinic to predict disease or to tailor treatment to a patient’s personality traits. But perhaps more important is using this knowledge to keep people healthy, says UC Riverside’s Friedman. “We can’t expect physicians to undo all the habits that began in their patients’ lives many years before,” he says. “Nor should we attempt to make everyone highly conscientious and expect them to follow the same path to college and beyond.”

Instead, Friedman urges a conceptual shift in how we think about health. “It is much more than the absence of disease,” he says. “We need to put more emphasis and resources on prevention, and we need to emphasize the social and educational variables that we now know lead to good health—having a purpose, meaningful work, positive social ties and the leisure to enjoy nature. Ultimately, the study of personality and disease is so important because it forces us to think about what it means to be a healthy person,” he says.