Discrimination and prejudice are serious social issues in today’s society, but who knew they were also a biological issue?

According to new research from Northwestern University, everyday feelings of discrimination can do weird things to the body’s hormones, particularly the stress hormone cortisol. They also found that the teenage years are a critical time in terms of sensitivity to discrimination, in terms of the effect on adult cortisol levels.

One of the first studies to look at the biological impact of prejudicial treatment, the research looked at both black and white experiences to compare the two.

"We found cumulative experiences matter and that discrimination mattered more for blacks," said study lead author Emma Adam, a developmental psychologist at Northwestern's School of Education and Social Policy, in a press release. "We saw a flattening of cortisol levels for both blacks and whites, but blacks also had an overall drop in levels."

Adam said the surprise came when researchers saw that discrimination during adolescence was particularly harmful.

Using data that had been collected over 20 years, the team showed that the more discrimination people faced during their early adulthood, the more dysfunctional their cortisol rhythms were by age 32. Cortisol is released during times of stress, along with several other hormones. Ideally, these levels are high in the morning to give us energy for the day, and they slip down at night as we prepare for slumber.

Having unusual or flattened cortisol levels is most commonly linked with disturbed mental health, higher fatigue, cardiovascular disease, and cognitive problems involving memory.

"We've been trying to solve the mystery behind why African-Americans have flatter diurnal cortisol rhythms than whites," said Adam, a faculty fellow at Northwestern's Institute for Policy Research.

There has been a fair amount of research on how discriminatory behavior affects individuals at that moment in time, according to Adam, but not a sufficient amount on long-term effects. This study offers the first empirical demonstration that discrimination can affect us biologically, and in ways that accumulate over time.

The study even controlled for other factors including income, education, depression, wake up time, and other health behaviors. Adam said that it was unlikely these other factors played a role.

"Adolescence might be an important time period because there are a lot of changes in the brain and body," Adam said. "When you experience perceived discrimination during this period of change, it's more likely that those effects are built into the system and have a bigger impact."

Source: Adam E, Heissel J, Zeiders K, Richeson J, Ross E, Ehrlich K, et al. Developmental histories of perceived racial discrimination and diurnal cortisol profiles in adulthood: A 20-year prospective study. Psychoneuroendocrinology. 2015.