A group of Wisconsin nuns in the 1930s proved that positive personality traits can add years to your life. Being disagreeable, on the other hand, can be deadly

Studying a group of nuns over their lifetimes, researchers were able to determine that certain personality traits contributed to longevity Photograph: Giuseppe Lami/EPA

On this day in 1930, the Mother Superior of the School Sisters of Notre Dame in Milwaukee, Wisconsin, sent a letter asking every member of the sisterhood to write an autobiography. She offered few further instructions, and so left it up to each member of the order to decide how to describe the most important episodes of their lives. Some nuns chose to insert emotional details about how their experiences had affected them. Others recounted only bald facts.

Seven decades later, researchers at the University of Kentucky found that these differences were strong predictors of how long the 180 nuns in their study lived. The more the sisters couched their accounts of personal responses to major life events in positivity, the greater their longevity.

The great benefit of studying nuns is that on all the common lifestyle factors that tend to affect longevity – living conditions, access to health care, marriage (or lack of it) – nuns live virtually identical lives to one another. The autobiographies were written when the Notre Dame sisters were around 22 years old. So this study suggests that enduring tendencies and coping mechanisms, when extended throughout our adult lives, matter substantially for health and lifespan.

These days, psychologists have reached a consensus on a more thorough way to measure personality than merely degree of positivity: they score individuals along five dimensions.

These dimensions, known as the Big Five, are each continuums: from pure introversion to exaggerated extraversion, for example, or neurotic nervousness to complete confidence. Together the Big Five compose the acronym Ocean –openness to experience, conscientiousness, extraversion, agreeableness and neuroticism (or emotional stability) – and are typically assessed using a questionnaire. Over time, researchers have come to realize that personality is at least as good at predicting longevity as socioeconomic status.

That may sound implausible, but records of 1,500 Hawaiian students illustrate how personality types can play out. In the early 1960s, some elementary school teachers in Hawaii were asked to assess each member of their young class for the Big Five dimensions.

Forty years down the line, early childhood scores for a few of these dimensions correlated strongly with a roster of risk factors for chronic illness: smoking, alcohol consumption, and excessive body mass among them.

For both sexes, the more conscientious elementary schoolers were the ones who grew into healthy adults at middle age.

For women only, smoking in one’s 40s was associated with low agreeableness (or conformity) scores in elementary school – perhaps, the study authors suggest, because these women became hooked on nicotine when smoking was considered a more rebellious behavior for women than it was for men.

Conscientiousness is undoubtedly the personality trait that matters most for longevity. It is also a remarkably stable trait across whole lifetimes. The direct health benefits of being an orderly, goal-directed person, able to control your impulses, are intuitive: not only do they mean you are psychologically equipped to resist a second slice of cake, but also that you do a good job of adhering to a doctor’s advice when you get sick.

Conscientiousness is what separates Sardinians with lots of “good cholesterol” from those with too much “bad cholesterol”; it is what predicts which patients with poorly functioning kidneys are going to snuff it first.

There are indirect advantages to conscientiousness, too. It is an excellent predictor of college GPA, even when the influence of high school SAT scores is removed using statistics. As a result, the conscientious tend to get better jobs, and in turn, better healthcare. The overall medical advantages that stem from conscientiousness are so substantial that possible methods to instill the trait have been put forward as public health policies, and medical researchers have called for measures of conscientiousness to be included in patient records.

For the remaining Big Five, the relationship with lifespan is less straightforward. Neuroticism implies never waiting long to see a doctor about a niggling medical worry, although – and unlike the long-lived nuns – a tendency towards low mood and poor ability to manage life’s stressors. Extroverts are probably good at seeking support when they need it, but they can be drawn into risky behaviors.

For agreeable people, the world is a more trustworthy place, and so they often enjoy high quality personal relationships. Yet in their obedience, the agreeable can do things they may later regret. (For example, agreeable people were especially willing to deliver a high-voltage electric shock in a Milgram-like experiment.) The fifth member of the Big Five, openness (aka creativity), can also be good or bad for health, depending on what exactly it is that an open person seeks to explore.

To clarify the health impacts of these conflicting influences, groups of Big Five researchers have mushroomed all over the world, with the intention of figuring out the common personality traits among longevity’s high achievers: the world’s centenarians. These scholars have accessed of personalities of people over 100 years of age living in Tokyo, Sweden, and the southern state of Georgia, among other places. In Australia, researchers used one-hundredth birthday letters from Queen Elizabeth II as proof of age.

Although not all centenarian studies have found the same results, generally, people who make it to very old age are predominantly emotional stable (ie non-neurotic) extroverts – in addition to being highly conscientious. In Baltimore, researchers studying the elderly calculated exactly how much this combination of traits contributed to survival. Having scores for extraversion and conscientiousness one standard deviation above average, and a score for neuroticism one standard deviation below average, adds two or three more years of life, they report.

Like the sisters of Notre Dame – many of whom wrote their autobiographies from a convent in Baltimore – these retirees were blessed with the intrinsic skills to navigate what life threw at them with aplomb. Their lesson to the unconscientious, to the natural introverts and hypochondriac wallowers out there, is to recognize how your own behavioral tendencies could be impacting your health, and take steps to address them. One day, your life may depend on it.