A hormone released by fat cells that is associated with a reduced risk of type 2 diabetes could also protect against depression.

Blood levels of the hormone adiponectin are positively correlated with insulin sensitivity. Xin-Yun Lu at the University of Texas at San Antonio and her colleagues manipulated levels of adiponectin in the blood and brains of mice, and assessed the animals' likelihood of exhibiting depression-like behaviours in response to stressors. The researchers found that mice with low blood levels of the hormone were more likely to show signs of depression than were control animals. Injecting adiponectin-neutralizing antibodies into the mouse brain also increased the likelihood of depression-like symptoms. By contrast, injecting adiponectin into the brain had an antidepressant-like effect in both normal-weight and obese, diabetic mice.

The findings could explain why depression is twice as prevalent in people with type 2 diabetes as in the general population.

Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1202835109 (2012)