Here's a great scientific reason to be nice. American psychologists have shown that having a hostile attitude could be bad for your health, especially if you are someone judged by society to be of lower social status.
Benita Jackson and colleagues measured the hostility and lung function of 4,629 healthy participants aged between 18 and 30 years, living in Minneapolis, Birmingham, Chicago or Oakland, USA.
Reduced lung function is a risk factor for chronic obstructive pulmonary disease – the sixth most common cause of death worldwide. Greater lung capacity in youth is known to provide protection from the illness later in life. Meanwhile, hostility is associated with immune functioning and hormonal activity, and it's via these biological pathways that the researchers predicted hostility might have an adverse effect on lung function.
Lung function was gauged by asking participants to wear a nose clip and blow into a machine. Hostility was measured by participants' agreement with statements like “I am easily angered” and “I strongly defend my own opinion as a rule”.
Those participants who were more hostile in nature also tended to have relatively poorer lung function, regardless of whether they were a smoker or not. This could leave these participants at greater risk of pulmonary disease later in life.
“It appears that hostility hurts, insofar as it is associated with lowered pulmonary function,” the researchers said.
The association held true for black men and women, and white women, but did not quite reach statistical significance for white men. The researchers surmised this could be because black people and white women who have a hostile demeanour are chastised by society for their attitude, thus causing them harmful stress. By contrast, a hostile demeanour in white men might be treated by society as a sign of authority.
The cross-sectional nature of the research means a causal link between hostility and lung function has not been irrefutably established. It's possible, though intuitively unlikely (given the levels talked about here), that poorer lung function causes hostility, and it's also possible that one or more unknown factors have a concurrent effect on both lung function and hostility.
Jackson, B., Kubzansky, L.D., Cohen, S., Jacobs Jr., D.R. & Wright, R.J. (2007). Does harbouring hostility hurt? Associations between hostility and pulmonary function in the Coronary Artery Risk Development in (young) Adults Study. Health Psychology, 26, 333-340.