According to a new study, men and women have different immune responses to bipolar disorder. The findings have big implications for future diagnostic tests, as well as treatment for men and women with this disease.
Researchers have long observed that men and women experience the effects of bipolar disorder differently. In particular, women with the condition experience depressive episodes, mixed mania, and rapid cycling more often than their male counterparts. Women are also more likely than men to experience post-traumatic stress disorder, migraines, and disruptions in their sleep pattern that lead to dysregulated mood. Bipolar prevalence also varies between the sexes, with bipolar II more commonly seen in women than men.
Penn State researchers also note that bipolar disorder also alters the immune system, causing low but potentially harmful inflammation in the brain. "When a person has mania or depression, certain parts of their brain are affected," said Erika Saunders, professor and chair of psychiatry at Penn State College of Medicine, and the study’s senior author. "For example, the hippocampus, which is important in memory formation, shrinks, and the connections between different parts of the brain are affected. We think that inflammation is playing a role in some of those changes that are then associated with poor functioning in bipolar disorder."
Given these observations, Saunders’ team hoped to identify some immune differences that would distinguish bipolar in men versus women. They analyzed immune biomarkers for 27 participants with bipolar disorder versus 31 participants who were otherwise healthy. Specifically, the team measured two immune system factors, zinc and neopterin, both of which are involved in inflammatory responses.
When the data were compared between the healthy versus the sick group, the team found small differences in zinc levels – people with bipolar disorder seemed to have lower levels of zinc than healthy people.
However, when the researchers looked at differences between the genders, more striking differences emerged for both biomarkers. In particular, both biomarkers seemed to be linked to the severity of depression or mania and the person’s gender. For example, women who had high concentrations of zinc were more likely to experience worse depression, whereas men with high concentrations of neopterin were more likely to experience worse mania.
Of note, the results deviate slightly from previous studies which found zinc deficiency to be associated with depression. Saunders and her team plan on investigating this surprising result, and they suspect zinc levels may be different in blood versus the brain. And as such, the authors are quick to caution against any self-medication with zinc supplements.
“What we are aiming for ultimately as a field and as a research group is to have a blood marker that we can use in the clinic that will help us predict when someone is developing a bipolar episode, and conversely when a treatment is working," Saunders said. "The work that we're doing in conjunction with the work of others across the country is understanding each individual factor that can then be put together in a larger way."
The results of the study suggest there are differences at the cellular level for men and women with bipolar disorder. And if these biological differences can be further teased apart, we may be able to improve diagnosis and treatment for people with the disorder.
Additional source: Penn State