A team of researchers based at the Renmin Hospital of Wuhan University in China has identified a possible link between a type of gut bacteria and depression in women who have not yet entered menopause.

The microbe, Klebsiella aerogenes, was found to break down a form of estrogen called “estradiol.”

Estradiol is a female sex hormone produced by the ovaries, placenta, and adrenal glands. It plays a vital role in the reproductive system, helping to regulate the menstrual cycle, ovulation, and pregnancy. Estradiol also affects bones, cholesterol levels, and other tissues in the body. Additionally, it has been shown to have an impact on mood and cognitive function, with lower levels of estradiol being linked to an increased risk for depression, anxiety, and other mood disorders.

K. aerogenes is a species of gram-negative bacteria commonly found in the environment, particularly in soil and water. While it is typically considered a harmless commensal bacterium in the human digestive system, it has been associated with opportunistic infections in people with weakened immune systems, particularly in hospitals where it can spread through contaminated medical equipment. These new findings suggest that there could also be an association between this type of gut bacteria and depression in women.

What the gut bacteria and depression study found

The study measured blood estradiol levels in 189 premenopausal women. The researchers found that average estradiol levels were almost 43% less in women with depression. This was compared to those who did not have the mood disorder.

Researchers then took gut bacteria from fecal samples provided by the volunteers and mixed them with estradiol. After doing this, they found that the gut bacteria from depressed women broke down the estradiol more rapidly compared to the bacteria from non-depressed women.

The team identified K. aerogenes as the microbe responsible. It also found that it was 14 times as prevalent in stool samples from participants with depression as those without.

Additionally, female mice fed K. aerogenes for four weeks displayed more depressive symptoms than those not given the bacterium.

The findings suggest that K. aerogenes could be contributing to depression in women. However, it is currently unclear how significant of an effect the microbe has on mood in humans. The study could, however, guide the development of new drugs targeting specific microbes and their metabolic processes.

The study appears in the April 4, 2023 issue of the journal Cell Metabolism.

Photo by Edward Jenner