You may have heard how excellent gut health benefits both physical and mental health. It might have been hard for you to imagine when you first heard it.
Why not? It's difficult to envision how the intestine, far down in the torso, can be linked to the brain. They're literally miles apart.
Yet, the gut-brain axis is a thing, and you may be less prone to stress-induced depression if your gut microbiome is healthy.
Can gut issues cause depression?
Yes, gut issues may lead to depression.
Researchers have recently discovered how gut health can impact mental health. There is an intestinal immune cell that impacts the gut microbiota (total microorganism in the gut), which consequently affects brain functions associated with stress-induced behaviors like depression. These immune cells are known as intestinal gamma delta cells.
In a healthy gut, there's a favorable balance of bacteria, fungi, and viruses. Previous studies suggest that stress-induced disorders like depression may result when there's an imbalance in the gut microbiome.
So researchers from Johns Hopkins Medicine went ahead to conduct another study to understand how that imbalance may lead to depression.
They conducted the study in mice by subjecting them to stress.
Studying gut bacteria and depression in mice
Some of the mice were stress-resilient, i.e., they didn't show psychiatric symptoms when subjected to stress. Others showed social avoidance, a depression symptom, under the same conditions.
On analyzing the mice's fecal matter, the researchers discovered the stress-prone mice had less L. johnsonii, a good bacteria, in their gut. Those that remained normal under stress had more good bacteria in their gut.
And when the stress-prone mice were given the good bacteria L. johnsonii, they stopped exhibiting psychiatric symptoms when under stressful conditions.
So it was pretty evident and a proof of what we originally knew: stress-induced depression symptoms may result from a gut microbiome imbalance.
But there's a nagging question: what causes that imbalance in the first place?
What causes gut microbiota imbalance leading to depression?
Remember the immune cells (intestinal gamma delta cells) we mentioned earlier?
There's a protein receptor known as dectin-1 found on the surface of these immune cells. This receptor instructs immune cells to act in certain ways, which may involve altering the microbiota balance in the gut. Consequently, it may lower the amount of good bacteria, resulting in stress-induced depression symptoms.
The researchers found that the protein receptor dectin-1 increases under stress, thereby altering the microbiota to a large extent and consequently leading to social avoidance.
When the stressed mice were given L. johnsonii, the dectin-1 receptor went to normal levels, and their mood stabilized.
Amazing, and what does that tell us? Increasing L. johnsonii levels and targeting the dectin-1 protein receptor in the gut could be a potential treatment for stress-induced mental issues.
Gut bacteria and depression in humans
The researchers went ahead to conduct a similar study on humans. This time, it was explicitly for depression and anxiety.
People with a higher abundance of lactobacillus in their gut had a lower risk of depression and anxiety when under stress. Those lacking this "good" bacteria were more likely to exhibit stress-induced depression and anxiety.
The study indicates that the amount of lactobacillus in the gut may influence how one responds to stress and the onset of depression and anxiety.
The good news here is this. In addition to probiotic (good bacteria) supplements, developing drugs to target those receptors in the gut may be a breakthrough in preventing stress-induced disorders like depression and social avoidance.