Like most chronic conditions and their symptoms, there is not one single cause for depression. Rather, there are several different factors which can contribute to and cause depression. When depression is not a by-product of external events, it is called endogenous, meaning “originating from within.” This kind of depression is believed to be fundamentally due to biochemical abnormalities, specifically an altered balance of the neurotransmitters serotonin, norepinephrine, and dopamine. This imbalance may occur in a number of different ways.
1) Amino acids—the building blocks of protein—are the source material for manufacturing these important brain neurotransmitters. Research has shown that imbalances or deficiencies in amino acids are very significant factors contributing to depression as they play an important role in the central nervous system’s regulation of autonomic processes including mood, energy, sleep patterns, and pain threshold. For example:
- Low levels of tyrosine or phenylalanine can result in abnormal levels of mood regulating chemicals in the brain, such as dopamine.
- Low levels of tyrosine can also cause subnormal levels of thyroid hormone. Such low levels are a well-known cause of depression.
- Low levels of S-adenosyl methionine (SAMe) have been linked to depression, though there is still inadequate research to explain the exact reason for this.
- Low levels of tryptophan—what the body uses to make the hormone serotonin—can spur an increase in depressed mood states.
2) Thyroid dysfunction, as stated previously, is a commonly observed cause of depression. Research has shown that hypothyroidism, especially lower levels of the potent thyroid hormone triiodothyronine (T3), is closely linked to mood symptoms such as depression.
3) Food and environmental allergens have also been closely associated with depression, and although some research has produced mixed results, double-blind trials have shown that food allergies can actually trigger mental symptoms, including depression.
4) Circadian Rhythm Disorder and Seasonal Affective Disorder produce depression. This is primarily due to an imbalance of the hormone melatonin, which is sometimes referred to as the body’s built-in biological clock due to its primary role in the orchestration of so many aspects of the sleep/wake cycle. Moreover, disrupted secretion patterns of melatonin can seriously interfere with sleep, thus aggravating symptoms of existing depression.
5) Dysfunction of adrenal hormones is a very significant factor in depression. An overactive Hypothalamic-Pituitary-Adrenal (HPA) axis—the body’s stress-regulation center—has proven to be a catalyst in the initial onset and progression of depression due to its secretion of heightened levels of the adrenal hormone cortisol. This is especially true when stress and obesity are also part of the clinical equation, because under both circumstances the HPA system may become hypersensitive (and thus overactive) and secrete dangerously high levels of cortisol. The adrenal hormone DHEA (a precursor of testosterone), levels of which decline with age, is responsible for counteracting or balancing out the effects of cortisol and elevating mood. Thus, it could be an important link to depression, especially when it occurs in a person over the age of 40.
6) A poorly functioning digestive system (or gastrointestinal tract) can result in the malabsorption of key nutrients necessary for maintaining healthy mood patterns and overall feelings of well-being, anxiety and depression. Low gastric acidity (a condition known as Hypochlorhydria) can lead to bacterial overgrowth in the small intestine. This in turn interferes with protein digestion and hinders the crucial task of amino acids to produce neurotransmitters; thereby potentially leading to the chemical imbalances directly linked with depression. Poor digestion also enables a certain intestinal yeast, Candida albicans, to overgrow which can also trigger mood swings, depression, and anxiety.
7) Overexposure to heavy metals, such as mercury and lead, has been clinically shown to induce psychiatric symptoms of depression and anxiety. Norwegian researchers found that 47% of patients with dental amalgam fillings reported suffering from major depression, compared to 14% in the dental control group.
8 )Mineral nutrient imbalances, such as magnesium and zinc, can also cause mood disorders such as depression.
9) An imbalance of glucose or insulin has also been shown to play a role in depression, as both are extremely important in proper brain functioning. Fluctuating glucose, or blood sugar, levels (as seen particularly in diabetic patients), can result in increased depression, tension, and fatigue. One important function of insulin is to facilitate the transport of the amino acid tryptophan, thus promoting increased production and activity of serotonin (an important mood regulator). These two critical factors are thus understandably linked to the presence of depression.1
10) A deficiency of omega-3 fatty acids, found primarily in fish oil, is yet another significant contributing factor to depression. For optimal brain functioning, there must be balance of both omega-3 and omega-6 fatty acids, and yet most people simply do not get enough omega-3 fatty acids from their diets. Some researchers speculate that this may explain why we have seen a significant rise in the number of Americans suffering from depression and other related mood disorders over the past several decades—with the age of onset growing younger and younger. In contrast, studies have shown that in areas where fish is consumed in great abundance, such as Japan, Hong Kong, and Taiwan, there is a surprisingly low incidence of depression and other chronic conditions such as heart disease.7
11) Depression is statistically twice as likely to affect women than men. Although this number may not be truly accurate due to the fact that men are much less likely to report depressive symptoms, it does represent another significant factor in the cause of depression. Female hormone imbalances, especially estrogen, can negatively impact the balanced functioning of the HPA axis and cause increased secretion of cortisol, which will in turn lower mood and, in many cases, cause depression.
12) As touched on above, pioneering researchers believe that depression is another symptom of Candida overgrowth—or more specifically, the 80 plus poisonous toxins and neurotoxins that candida yeast can produce inside the body. It is this toxic waste that they believe to be the primary cause of depression, especially for the chronically ill. These toxins can mimic and interfere with many of the body’s hormones. When this happens, feelings of intense depression may be induced.
In addition to the toxins put off by the yeast itself, Candida also survives by manufacturing toxic substances from refined carbohydrates and sugars in the digestive system. Hypersensitivity to these Candida yeast toxins, the most harmful of which is acetaldehyde (a by-product of alcohol and the chemical that naturally causes a “hangover”), can lead to anxiety, depression and impaired intellectual functioning. Sadly, this often is not recognized as a problem of Candida and will usually result in psychiatric referral. But if the problem is actually physiological and the treatment is psychological, there is little hope for success. When the treatments are unsuccessful, this increases feelings of guilt, poor self-esteem, and depression.
12) There are also certain drugs and medications that can cause depression. These include Tagamet®, Inderal®, narcotics, benzodiazepines, birth control pills, sleeping pills, prednisone, alcohol, and marijuana.
Additional Information about Depression
- Depression Overview
- Common symptoms of depression
- Help me choose a natural and alternative treatment for depression
- Dietary and lifestyle recommendations that may help in the treatment of depression
- Conventional or prescription medications used in the treatment of depression
- Additional Reading for depression