If you or someone you know suffers from depression, this article might be worth a read. The authors claim that supplemental magnesium can help to lessen feelings associated with depression. They give enough scientific and anecdotal evidence that makes magnesium worth pursuing in trials.
Rapid Recovery From Major Depression Using Magnesium Treatment, George A. Eby and Karen L. Eby, Medical Hypotheses, 2006
The link above is to a pdf of the whole article but here are exerpts from the abstract to give you a feel for it:
Magnesium deficiency is well known to produce neuropathologies.
Only 16% of the magnesium found in whole wheat remains in refined flour, and magnesium has been removed from most drinking water supplies, setting a stage for human magnesium deficiency.
Magnesium ion neuronal deficits may be induced by stress hormones, excessive dietary calcium as well as dietary deficiencies of magnesium.
Dietary deficiencies of magnesium, coupled with excess calcium and stress may cause many cases of other related symptoms including agitation, anxiety, irritability, confusion, asthenia, sleeplessness, headache, delirium, hallucinations and hyperexcitability, with each of these having been previously documented.
They do indeed document their claims.
Interesting that taking supplemental calcium can cause a relative magnesium deficiency. This is a risk from taking any isolated supplement; it can create imbalances.
They presented 4 case studies. I’ve summarized them below:
1. A non-drinking, 59-year-old hypomanic-depressive male, having had a long history of mild depression treatable with antidepressants, suddenly became extremely anxious, insomniac, tetanic and suicidally depressed after a year of extreme personal business and noise stress and poor dietary habits (fast food). He was not responsive to treatment
with a number of antidepressants and lithium carbonate. After reviewing the report of Durlach concerning magnesium and depression , he was treated with magnesium. He was given 300 mg of magnesium, as glycinate and later as taurinate, to take orally with each meal and at bedtime.
The first night after starting magnesium, sleep was restored essentially to normal. Within the following 4 days, depression was greatly reduced for 4–6 h after each magnesium
dosage. Anxiety steadily disappeared. Tetany and headaches rapidly disappeared.
In this patient, depression always occurred 1 h after taking a 500 mg calcium (carbonate) dietary supplement, which was extinguishable within 1 h only by administration of 400 mg of magnesium. This man was extremely sensitive to calcium, and elimination of all dairy and supplemental forms of calcium was mandatory for mental stability. [Eby and Eby describe the mechanism behind this.]
2. A 23-year-old woman, who had 5 years previously suffered traumatic brain injury and lost much of her short term memory and some of her IQ, suddenly became severely depressed after experiencing long-term stress due to several stressors related to diet (fast food), work, constant noise, and especially because of very poor academic performance after having had excellent grades prior to her brain injury. Antidepressants had beneficial effects, but her concern about side effects caused her to switch to magnesium. She was given 200 mg of magnesium (as taurinate) to take with each meal and at bedtime.
After 1 week of magnesium treatment, the woman became free of depression. Unexpectedly, her short term memory and IQ also returned, benefits only previously shown in rats  when immediately treated with magnesium after traumatic brain injury. However, her mental acuity returned nearly immediately upon magnesium treatment, even though the trauma had occurred 5 years earlier.
3. A 35-year-old woman, having had three children followed by severe postpartum depression (PPD) in each case, was given 200 mg of magnesium (as glycinate) to take each meal during her pregnancy to prevent PPD during her fourth pregnancy. Antidepressants had previously had some beneficial effects, but side effects were worrisome to her. Part of her decision to take magnesium was her desire to prevent preeclampsia, a known but often ignored magnesium deficiency condition.
The woman delivered her baby on schedule without developing any aspect of postpartum depression, preeclampsia or any other illness associated with pregnancy. The baby was healthy, full weight and quiet.
4. A 40-year-old man, irritable, anxious, extremely talkative, moderately depressed, and heavily into use of food, tobacco (smoking and chewing), alcohol and cocaine, took 125 mg of magnesium (as taurinate) with each meal and at bedtime in an effort to relieve his symptoms.
The man found himself free of his symptoms within a week, and unexpectedly found his craving for smoking, dipping, cocaine and alcohol to disappear also. It seemed that magnesium deficiency caused his habituation. He also noted that his ravenous appetite was suppressed, and beneficial and desired weight loss ensued.
What is “dipping”?
While reading this, I thought many of these effects were too good to be true. Also, you have to be careful with case studies. They don’t account for the placebo effect. But in their Discussion section, they describe mechanisms and cite studies to back up their findings in these cases. It’s extraordinary that more work hasn’t been done on the link between magnesium and depression.
I’ve written about how magnesium improves sleep. (In fact, they cite one of the best magnesium/sleep studies done on humans to date, which I covered here.) Insomnia is not a mental illness in itself, but is thought to be a symptom of mental illness. The National Alliance on Mental Illness says, “more than one-half of insomnia cases are related to depression, anxiety or psychological stress.” Perhaps magnesium improves sleep because it improves symptoms of anxiety and depression?
I saw this article cited on Magnesium and the Brain: The Original Chill Pill, Emily Dean MD., Psychology Today, June 2011