New research shows those with depression have a five percent larger hypothalamus than those who don’t have the illness.
The hypothalamic-pituitary-adrenal axis (HPA axis), is the system that responds when we are under stress by releasing cortisol into the body, giving us more energy to react to a challenge, and then returning the body to its natural state when the stressor has been removed.
In those with mental illness, the HPA axis is dysfunctional and releases cortisol even when no real stressor is present due to the over activity of the hypothalamus. It is unclear whether the increased hypothalamus activity is leading to its increased size or not.
Regardless, the larger size could explain the increased levels of cortisol and the periods of tension often experienced by those with depression.
Source: Max Planck Institute for Human Cognitive and Brain Sciences. “In depression the brain region for stress control is larger.” ScienceDaily. ScienceDaily, 20 September 2018.