Most people don’t consider their personality when they consider their health — and they should. A 1997 study published in the Journal of Personality and Social Psychology concluded personality traits are a great indicator of health-risk behavior.

The study was the first to examine the long-term effects personality has on health, where researchers followed 3-year-old children born in New Zealand in 1972-3 through their 21st birthday. At 3, researchers observed children’s temperaments; at 18, they administered a personality questionnaire; and at 21, they identified risky behaviors, such as alcohol abuse, unsafe sex, violent crime, and dangerous driving.

While over three quarters of participants didn’t participate in risky behavior, or only identified with a single risky behavior, “young adults who did engage tended to be non-traditional, not to avoid harmful situations, be less in control and careful, less social, and more aggressive than the control group.” Interestingly, researchers found children they classified as “under-controlled” at a mere 3 years old — or unable to sit still, were impulsive and irritable — were more likely to engage in risky behaviors when they turned 21.

Anti-social and aggression are two traits associated with introversion, one of the two major personality types; the other is extroversion. The key word is associated as there tend to be a lot of misconceptions surrounding each personality type. For example, it’s not right to say every introvert is a violent recluse or every extrovert is a happy-go-lucky person who always plays by the rules when those are just two extreme ends of the spectrum.

But, it is interesting to see how a child’s personality predicted risky behaviors later in life, namely behaviors known to lead to disease. Drinking too much is a primary example of how people hurt their health. The Centers for Disease Control and Prevention estimated excessive alcohol lead to 88,000 deaths and 2.5 million years of potential life lost each year in the United States between 2006 and 2010. High blood pressure, heart and liver disease, as well as liver cancer and mental health problems, like depression, are other long-term health risks linked to alcohol abuse.

Here are additional studies on the health differences between introverts and extroverts.

Obesity

The obesity rate in the United States continues to climb, with one computer program predicting it now cuts up to eight years off a person’s life. To see if personality influences a child’s eating behavior, a team of researchers at the Cornell Food and Brand Lab served elementary school children breakfast in a small or large breakfast bowl. Children indicated how much cereal and milk they wanted, while later on in the study, children were able to serve themselves.

When serving themselves, extroverted children (as decided by attending teachers and counselors) served themselves 33 percent more breakfast in the large bowl compared to their introverted classmates. This feeds into the idea extroverts rely more on environmental (or sensory) cues rather than internal cues, like introverts. In this case, the breakfast bowls are the children’s cues.

And yet, when both extroverted and introverted children were served in a small bowl by another person, they each requested 50 percent more food. Since this is the case, more research would need to be done in order to conclude whether or not extroverts are for sure more likely to be obese. 

Obesity, regardless of personality type, seriously harms health, increasing risk for cardiovascular disease, musculoskeletal disorders, like osteoarthritis, and certain cancers. 

Mental Health

The American Psychiatric Association added “introverted personality disorder” to their Diagnostic and Statistical Manual over 30 years ago; The World Health Organization has made a similar classification. While experts have argued a preference for quiet and contemplation shouldn’t necessarily mean a person has a personality disorder, separate research has confirmed introverts are prone to depression.

One study published in the Journal of Psychiatric Research found 74 percent of introverts made up the depression population, while another study published in the Journal of Personality found those who felt or acted more extroverted in daily situations were happier no matter the cultural setting. Additionally, there's research that suggests introverts experience reduced psychological well-being, as well as face a higher risk for suicide. This speaks to the hallmark (and often misunderstood) sign of introversion: retreat. 

"At the heart of it, introverts and extroverts respond really differently to stimulation," Susan Cain, author of Quiet: The Power Of Introverts In A World That Can't Stop Talking, told The Huffington Post. "Introverts feel most alive and energized when they're in environments that are less stimulating — not less intellectually stimulating, but less stuff going on."

There may also be something of introverts being more aggressive. A more recent study found dreams about murder and killing mirror real-life aggression, hostility, and — yep —   introversion. Study authors said emotions in dreams can be much stronger than emotions people, and if introverts are having more aggressive dreams, they may be keeping their feelings bottled up.

Immune System

When it comes to the overall immune system, extroverts have an advantage, according to research from the University of Nottingham. Researchers tested 121 healthy adults to determine the five basic aspects of personality, including openness, agreeableness and neuroticism. Then, they used microarray technology to examine the connection of reported traits and performance of white blood cells, which play a vital role in protecting the body against infectious disease.

The results showed those who identified more as an extrovert had better white cells, or immune system. And those who identified more as an introvert had a weaker immune system. This does not mean negative emotions dictate health issues; researchers were unable to make that conclusion. But it seems to further existing research and study.

This article originally incorrectly stated that the American Psychological Association prints the Diagnositc and Statistical Manual of Mental Disorders. It is printed by the American Psychiatric Association.