What fuck is it? Is it neurological? Hormonal? Behavioral ?
We don’t know.
Pharmaceutical companies claimed it’s due to not enough serotonin, but there really isn’t any evidence of that and animal studies suggest it’s wrong.
>The main areas of serotonin research provide no consistent evidence of there being an association between serotonin and depression, and no support for the hypothesis that depression is caused by lowered serotonin activity or concentrations. [https://www.nature.com/articles/s41380-022-01661-0](https://www.nature.com/articles/s41380-022-01661-0)
If you actually look at labels for SSRIs, you’ll see that the mechanism of how they work is unknown.
>The mechanism of action of citalopram is unclear [https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/020822s041lbl.pdf](https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/020822s041lbl.pdf)
It’s likely due to the brain not functioning properly in some way.
For your brain to work properly you need to exercise, have a good diet and good sleep. So when someone doesn’t do all of these then the brain won’t work properly and could show up as mental illnesses such as depression.
This is why sleep, diet and exercise are shown to have a causative positive impact on depression.
>The diet may have a significant effect on preventing and treating depression for the individual. A diet that protects and promotes depression should consist of vegetables, fruits, fibre, fish, whole grains, legumes and less added sugar, and processed foods. In the public health nurse’s preventative and health-promoting work, support and assistance with changing people’s dietary habits may be effective in promoting depression. From [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7084175/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7084175/)
>Current evidence supports the finding that omega-3 PUFAs with EPA ≥ 60% at a dosage of ≤1 g/d would have beneficial effects on depression https://www.nature.com/articles/s41398-019-0515-5
Sleep is really important, if you aren’t sleeping properly you have have a tenfold higher risk of depression,
>People with insomnia , for example, may have a tenfold higher risk of developing depression From [https://www.hopkinsmedicine.org/health/wellness-and-prevention/depression-and-sleep-understanding-the-connection](https://www.hopkinsmedicine.org/health/wellness-and-prevention/depression-and-sleep-understanding-the-connection)
Finally studies show that exercise is just as effective as medicine.
>Four trials (n = 300) compared exercise with pharmacological treatment and found no significant difference (SMD -0.11, -0.34, 0.12). From [https://pubmed.ncbi.nlm.nih.gov/24026850/](https://pubmed.ncbi.nlm.nih.gov/24026850/)