Historically, conventional science used to claim that depression stems from a chemical imbalance in the brain,1 such as if you have too much or insufficient amounts of a particular brain chemical.2 Most pharmaceutical-oriented solutions for this mental disorder revolved around this theory.3
However, the chemical imbalance theory is not entirely true — in fact, it was actually a massive marketing gimmick to promote the use of expensive and potentially toxic antidepressants.
Today, we know that depression is much more complicated than what was previously believed, and that it can stem from a wide variety of unexpected biological, environmental and psychological factors.
Chronic Inflammation: an Oft-Ignored Cause of Depression
A growing number of scientists are claiming that depression may primarily result from inflammation caused by your immune system.
In fact, depressive symptoms may actually be downstream manifestations of inflammation. This is because when cytokines, a group of proteins, trigger inflammation in your body, it causes your brain to go into “sickness mode.” 4
George Slavich, a clinical psychologist at the University of California, who has spent years studying depression, said:
“I don’t even talk about it as a psychiatric condition any more. It does involve psychology, but it also involves equal parts of biology and physical health.”
There is a lot of evidence supporting this claim, such as that people suffering from inflammatory diseases like rheumatoid arthritis5 are often at a higher risk of depression.
In cancer patients, a drug called interferon alpha causes depression, and here’s why: It boosts the patient’s inflammatory response to help fight the disease.6 Vaccines that lead to a spike in inflammation can also put people in a depressed state.7
Researchers also found that certain classes of depression such as postpartum depression, melancholic depression and bipolar disorder are actually linked to elevated cytokine levels, along with decreased cortisol (a stress hormone that also protects against inflammation) sensitivity.8
Experiencing a Traumatic Life Event Is Also a Potential Cause
Losing a loved one, relationship problems, financial issues, tragic accidents and other significantly painful life events can severely affect an individual, and research found that these types of traumatic events may play a role in your risk for depression.
In fact, a team of researchers studied this, with the goal of determining what role life events play in mental health. Based on surveys completed by almost 33,000 participants, they found that undergoing traumatic life events was the single biggest determinant of both anxiety and depression.
Other factors followed, such as family history of mental illness, education and income levels and relationship status.9
A Certain Gene Variant May Also Be a Primary Cause of Depression
Studies found that having low levels of brain derived neurotrophic factor (BDNF) are seen in depressed individuals, meaning it may be a primary cause for this ailment.
Further research confirms that an alteration known as a single nucleotide polymorphism (SNP) in the BDNF gene may also play a role in a person’s risk for depression, anxiety and memory loss. Having just one “letter” in the genetic code misspelled can already cause this alteration.
Twenty percent of Americans are said to have this BDNF alteration, which leads to neuron shrinkage in the hippocampus, reducing the connectivity between brain cells. One of the researchers emphasized:
“Just like hypertension contributes to the risk for heart disease, the BDNF alteration increases the risk of depression, anxiety and memory disorders — but is not the sole reason why they occur."10
The Link Between Optimal Brain Function and Your Gut
Inflammation specifically in the gut may have a possible role in the development of depression. Having poor levels of good bacteria in your gut can actually impact your mental health, leading not only to depression and anxiety, but even autism. It’s believed that a disruption in the gut-brain axis is the main cause of inflammation. Keep in mind that your gut is your second brain, as it is made from the same tissue as your brain during fetal development.
In fact, your gut bacteria are essential to serotonin regulation, as they actually produce more serotonin than your brain. A 2011 Hungarian scientific review highlights this link between the gut and the brain, stating that:11
• People with gastrointestinal inflammation and autoimmune diseases (brought on by chronic low-grade inflammation) suffer from depression, and may actually be a “neuropsychiatric manifestation of a chronic inflammatory syndrome.”
• Attenuating pro-inflammatory stimuli, which improves brain function, may help treat gastrointestinal inflammation and may be possible with the help of probiotics and vitamins B and D.
Lastly, Poor Vitamin D Levels May Be an Underlying Factor
Vitamin D deficiency has been a well-recognized cause of seasonal affective disorder (SAD), one of the common types of depression. This just stresses why getting enough sun exposure is crucial to your wellbeing. In a 2006 study, it was found that elderly people with vitamin D levels below 20 ng/ml are 11 times more likely to experience depression than those with higher vitamin D levels.12
So, if you’re dealing with depression, you might benefit from having your vitamin D levels checked so you can address any deficiency. The best way to optimize your vitamin D levels is through sun exposure, but if that’s not possible, taking a vitamin D3 supplement may be the next best strategy.