A little grumpiness, every now and then, is healthy. 

By Melissa Locker
December 08, 2018
Hero Images/Getty Images

What of the best lines in Steel Magnoliasis when Clairee says, "If you can't say anything nice about anyone, come sit by me." It's a delicious, hilarious jab at people who are too nice all the time. Not only are incredibly nice people boring at parties, but it turns out that they may also be more prone to developing mental illness, at least according to one scientific study.

The study, published in the journal Nature Human Behavior, showed that people who are nice, which the researchers defined as sensitive to unfairness or inequity, are more likely to show symptoms of depression than people who are more selfish and egotistical.

They made this determination by having 350 subjects take a personality test to help separate people into two groups: "pro-social" ((meaning self-sacrificing and willing to work towards equity) or "individualist" (selfish and primarily concerned with taking care of themselves). They then looked at people's willingness to share financial resources with those less fortunate than themselves by sticking the study participants in an MRI and seeing what part of their brains lit up during specific situations.

The researchers found that the brain patterns of the two groups reacted very differently to situations in which money was distributed unequally. Pro-social people showed a lot of activity in the amygdala (a part of the brain associated with feelings, including injustice and stress), while the so-called individualists had increased activity in the amygdala only when other people received more money than they did. There was also a different pattern of activity between the two groups in the hippocampus, another primitive brain region involved with automatic stress responses.

The researchers then gave the participants a questionnaire to help them determine whether these patterns of brain activity were linked with symptoms of depressions. Turns out that those with prosocial personalities and prosocial pattern of brain activity (the nice, generous types) were more likely to have symptoms of depression. That remained true when researchers followed up with participants a year later and when the experimenters controlled for age, gender and social status.

As Scientific American points out, the study doesn't necessarily mean that caring about other people will automatically lead to depression. That said, nicer people are more vulnerable to depression because they are more likely to be empathetic, feel guilty about inequity, and be stressed by unfairness. Thanks to the MRIs, the researchers know that this emotional sensitivity is hard-wired into their brains, too.

WATCH: Science Says People Who Are Always Late Are More Successful and Live Longer

That said, being kind and nice and sensitive to the plight of others, aren't guarantees of unhappiness, but they could make people more sensitive to depression. Keep an eye on your neighbors and friends and that person who volunteers for every committee at church and the PTA.