Although it is such a widespread problem, medicine is still at a loss to understand what depression is and its causes. At best, doctors believe that most cases of chronic depression are caused by a chemical imbalance-more precisely, by a low level of serotonin, a brain chemical and neurotransmitter that acts on the nervous system. As a result, every year, we take around $13bn (lb8bn)-worth of antidepressants, which include mostly SSRIs (selective sero-tonin reuptake inhibitors) such as Prozac (fluoxetine hydrochloride).
Neuroscientists believe that depression is a disorder of the brain, and magnetic resonance imaging (MRI) brain scans of depressed people indicate that it's the areas that regulate mood, thinking, sleep, appetite and behaviour that are functioning abnormally.
While these theories may hold sway, neither explains the initial cause of the chemical imbalance or why these parts of the brain are malfunctioning in the first place. Despite the 'single-bullet' approach of SSRI drugs, medicine at least recognizes that biochemistry is only one possible cause.
Depression can be many different diseases-from major depression, dysthymic (mood) disorder and psychotic depression to postpartum depression and seasonal affective disorder (SAD)-and, thus, has many causes-our genes, a separate illness, the environment or psychological factors (National Institute of Mental Health; www.nimh.nih.gov/health/publications/ depression/complete-index.shtml).
These days, doctors are having to deal with more cases of anxiety, such as post-traumatic stress disorder, obsessive-compulsive and panic disorders, and social phobia. These problems tend to escalate following a terrorist outrage or among soldiers returning from a war zone (Am J Manag Care, 2005; 11 [12 suppl]: S344-53).
But even this all-embracing view
of depression and its causes is sometimes contradicted by the research. Although doctors believe the gene theory must be right-and so look for cases of depression in family groups-individuals who don't have a family history of depression are just as likely to suffer from the condition (Tsuang MT, Faraone SV. The Genetics of Mood Disorders. Baltimore, MD: Johns Hopkins University Press, 1990).
Women are also far more likely
to suffer from depression, and this appears to support the chemical-imbalance theory, especially as depression is more common after giving birth, or in cases where pre-menstrual syndrome is especially severe, or during the menopause (Biol Psychiatry, 1998; 44: 839-50).
Yet, here again, this is only part of the story. The WHO has found that depression varies dramatically in different parts of the world. In South-east Asia, for instance, only 5 per cent of the population suffers from chronic depression, but the rate jumps to 25 per cent in Eastern European countries such as Hungary, Belarus, Latvia, Lithuania and Finland.
As we are all essentially similar in terms of our chemistry and biology, such geographical variations either contradict the prevailing view of depression and its causes or, at the very least, they suggest that some-thing else more complex is going on.
Isolation is a cause
Intrigued by the geographical and cultural differences in rates of depression, researchers Joan Chiao and Katherine Blizinsky, at North-western University in Chicago, IL, have discovered that even genetic tendencies to depression can be nullified by living in a collective or communal environment.
"A genetic vulnerability to depression is much more likely to be realized in a Western culture than an East-Asian culture that is more about we than me-me-me," said University spokeswoman Pat Vaughn Tremmel.
The research team found that
80 per cent of people living in East Asia are genetically susceptible to depression because they carry a variation of the serotonin transporter gene (STG) that invariably leads to depression. Yet, despite this greater proclivity, far fewer East Asians suffer from depression than those living in individualistic nations, such as the United States and Western European countries.
Collective or communal cultures may give people both tacit and explicit expectations of social support. "Such support seems to buffer vulnerable individuals from the environmental risks or stressors that serve as triggers to depressive episodes," said Dr Chiao, assistant professor of psychology at the Northwestern's Weinberg College of Arts and Sciences (Proc R Soc B: Biol Sci; published online October 28, 2009; doi: 10.1098/rspb.2009.1650).
Conversely, if communal living can override a genetic predisposition, it also suggests that depression is a disease of isolation and, so, can be triggered, or worsened, by a sense of loneliness and a lack of social support.
This view is supported by research into individuals who belong to a local church community that discovered, in one study of 230 church-goers, that such people are almost never depressed, not even when their income is low (Health Soc Work, 2008; 33: 9-21).
Stress is not a cause
Medicine's view of the causes of depression has been further questioned by another researcher at Northwestern who has described
the current dogma as "simplistic". Dr Eva Redei, of the Department of Psychiatry and Behavioral Science, says that her extensive research has revealed that depression is caused by neither stress nor chemical imbal-ance. As a result, mood-altering drugs such as the SSRIs almost never hit the target.
In laboratory studies, Redei and her team could find no overlap between stress-related genes and depression-related genes. In other words, chronic stress and depression are separate conditions-with little or no causal connection. Neverthe-less, doctors are more often than not prescribing antidepressants for cases of stress (presentation at The Society for Neuroscience Annual Meeting, Chicago, IL, October 2009).
Dr Redei has not been alone in questioning the chemical-imbalance theory. It has never been proven by any independent trial since the theory was first postulated in 1967. In fact, in a meta-analysis of all published as well as unpublished trials, researchers found that those trials financially supported by an
SSRI drug manufacturer either put
an unwarranted spin on the results or suppressed the study altogether if
the results did not support the theory (N Engl J Med, 2008; 358: 252-60).
In one study of serotonin, even people who were suicidal appeared to have levels of serotonin similar to those of healthy individuals, and healthy people whose serotonin levels were kept deliberately low didn't become depressed (Pharmacopsychiatry, 1996; 29: 2-11). In addition, depressed individuals who were given huge doses of serotonin failed to respond (Arch Gen Psychiatry, 1975; 32: 22-30).
So what exactly is depression?
Depression doesn't appear to be solely genetic, it probably isn't caused by stress and it almost definitely has nothing to do with an imbalance of serotonin. As depression is about to become the most prevalent chronic condition in the world, it's time that medicine reexamined its assumptions about the condition, and the way it is treated. For starters, here are some of the more likely causes.
u Social isolation. Depression appears to be a disease of loneliness and a sense of helplessness, as the latest research from Northwestern University suggests. Even severe cases of depression have been helped by the 'talk therapies', such as cognitive behavioural therapy (CBT), which gives the sufferer an opportunity to meet and talk with an empathetic listener.
u Hypothyroidism. One in five cases of chronic depression is caused by the body producing too little thyroid hormone. Although the condition is considered a genetic problem, the cause may be environmental, such as a diet that is deficient in iodine.
u Low blood sugar. Medically known as 'reactive hypoglycaemia', low blood sugar is the result of compulsive snacking on sweet or starchy foods. Removing carbohydrates from the diet can smooth out mood swings.
u Irritable bowel syndrome (IBS) and coeliac disease. Depression is a symptom observed in one-third of all sufferers of IBS. It is also commonly seen in those with coeliac disease, in which the inner lining of the small intestine is damaged by eating wheat, rye, oats or barley.
u Nutritional deficiency. The B vitamins apparently play an essential role in depression. Low levels of folic acid (vitamin B9) are frequently seen in people with chronic depression, as are low levels of B6 (pyridoxine), B2 (riboflavin) and B1 (thiamine). In the early stages of thiamine deficiency, normally healthy people become depressed, irritable and fearful.
Vitamin C deficiency is also important in maintaining an even tempera-ment and mood. The first symptoms of scurvy, the disease of vitamin C deficiency, are depression, tiredness and irritability.
Of the minerals, a lack of calcium, iron, magnesium and potassium can
all cause depression. Paradoxically, too-high levels of calcium can also induce depression.
WDDTY Volume 20 Issue 09