Microbiota and Depression: How Are They Related?

The state of our intestinal microbiota directly influences our nervous system and our behavior. How is this possible? In this article, we'll explain.

Written and verified by the psychologist Montse Armero.

Last update: 15 December, 2022

Microbiota and depression are two concepts that belong to different semantic nodes and that would appear to have nothing to do with each other. However, they’re actually related. In fact, to a greater extent than scientists thought just a few decades ago.

To date, in the 21st century, a large number of research teams have devoted significant resources to studying the digestive tract and how it influences other organs. The results show bidirectional communication between different systems. This means that what happens in one organ directly or indirectly affects other organs.

Gut microbiota

Intestinal microbiota were formerly known as intestinal flora. They’re a set of microorganisms that live in the intestine. There are about one hundred trillion of these microorganisms. They include more than 400 species of bacteria, various fungi, viruses, protozoa, and other microbes.

The gut microbiota have important roles in the physiology and pathophysiology of health and disease. Some of the most important are the following:

• Digestion and absorption of nutrients.
• Synthesis of vitamins K, B5, B8 (biotin), and B9 (folic acid).
• Intestinal absorption of iron, calcium, and magnesium.
• Synthesis of short-chain fatty acids (SCFA).
• Neuroendocrine regulation (gut-brain axis).
• Modulation of the immune system.
• Energy homeostasis.
• Barrier function against pathogens.
• Neurotransmitter synthesis.
• Regulation of intestinal transit.

The link between microbiota and depression

Some studies claim that the communication between the microbiota and the brain is bidirectional. They state that the nervous, endocrine, and immune systems are involved in this communication.

The microorganisms present in the microbiota produce substances that can cross the intestinal epithelium, enter the blood, cross the blood-brain barrier, and reach the brain. The reverse process also occurs. In other words, the nervous system acts on the intestinal bacteria and modulates them.

We now know that 95 percent of serotonin, is produced in the gut. Serotonin is one of the most important neurotransmitters in mood regulation. Other important agents in gut-brain communication are short-chain fatty acids (acetate, propionate, and butyrate), hormones such as cortisol, and neurotransmitters like GABA.

Altered microbiota and depression

The balance of the microbiota can be affected by multiple factors. For example, diet, antibiotics, chronic stress, a sedentary lifestyle, or a lack of continuous rest are some of the most important.

In fact, when the composition of the microbiota is altered and an imbalance is produced. This is known as intestinal dysbiosis. It can contribute to the appearance or worsening of the symptoms of depression.

As we explained earlier, the reverse process also occurs. Therefore, a depressive state can modify certain species of bacteria in the microbiota. In turn, the altered microbiota worsens the depressive picture.

Improving the condition of the microbiota

As human beings, we can’t control many of the external negative factors that happen to us. For instance, crises, pandemics, accidents, or deaths. Nevertheless, these are situations that can become extremely harmful. In fact, they can predispose us to suffer from depression.

However, we have great power to act on what happens inside us, both physically and mentally. Thus, given the knowledge we have today, it’s key that we take care of the factors that most influence the balance of the microbiota.

Diet

A diet based on real foods and not processed products is essential to maintain a good intestinal balance. The foods that are most recommended to consume for a low-inflammatory diet are vegetables, fruits, nuts, seeds, fish, eggs, and unprocessed grass-fed meat.

On the contrary, ultra-processed foods, and alcoholic and sugary drinks can cause inflammation in the intestine. Low-grade inflammation sustained over time favors the development of multiple, mostly avoidable diseases. For that reason, it’s important that we follow a diet that’s as little processed as possible.

Antibiotics and probiotics

Taking antibiotics destroys the balance of intestinal bacteria. Therefore, probiotics are increasingly prescribed alongside antibiotics. However, these don’t always comply with what’s described on the labels. In order to find out if a probiotic is of quality or not, the product description should be examined to see that it includes the following :

• Identification of genus and species of microorganisms.
• Strain designation.
• Storage conditions.
• Safety.
• Recommended dose.
• Exact description of the physiological effects.

Chronic stress

Chronic stress is one of the factors that most influence people’s psychological distress. In addition, it significantly alters the balance of the microbiota.

Because of this, it’s important that we look for ways to manage stress more adequately. Some of the most effective methods are practicing mindfulness, meditation, and taking nature walks. As a matter of fact, the undertaking of any kind of physical activity that gives us the chance to escape from our most harmful thoughts.

Physical activity

Done consistently, physical exercise increases the diversity of the gut microbiota. In addition to its myriad physical benefits, physical activity prevents certain diseases. For instance, colorectal cancer, obesity, anxiety, and depression.

Physical activity especially benefits people suffering from depression, stress, and anxiety. Not only does it improve mood, but the microbiota is also indirectly favored.

Insomnia

Bad sleep patterns over time alter many of the body’s functions. This includes the digestive function. Therefore, when we sleep badly, our digestion worsens.

In the long term, gut microbiota are also affected by poor quality sleep. For this reason, if we go through a time when we suffer from insomnia, it’s important to find a way to solve it.

Final thoughts on microbiota and depression

Every day, more research appears that links the balance of intestinal microbiota with mood. Obviously, we can’t always decide what experiences we’re going to live through. However, we can develop a proactive attitude toward everything that we’re able to control.

Taking care of our intestinal microbiota favors the correct functioning of our nervous system. That’s because it regulates neurotransmitters such as serotonin that are so important in cases of depression.

In addition, having healthy microbiota contribute to the balance of other systems that are so basic for our well-being. For example, the immune or endocrine systems.