Can drinking coffee relieve depression? What are the health effects of coffee?

There are a variety of conclusions about the effects of coffee on health, and people don't know what to do. Some say it's good for your health, others say it's bad-it's hard to know whether that cup of coffee in the morning is a health elixir or chronic poison.

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In a major recent study of caffeine, researchers at the Harvard School of Public Health found that drinking two to four cups of caffeinated coffee a day was associated with a reduced risk of suicide in adults.

The study, published in the World Journal of Biology and Psychiatry, is a meta-analysis of three large health research projects in the United States, involving 43599 men and 164825 women. Every four years, the subjects' intake of caffeine (from drinks such as tea, soda and Coca-Cola), coffee and decaffeinated coffee were assessed by questionnaire. Caffeine from coffee accounted for the vast majority of all three studies, accounting for 71%.

For deaths that occurred during the study, the researchers looked at death certificates to track the cause of death; 277 deaths were caused by suicide.

The analysis showed that adults who drank 2 to 4 cups of coffee (equivalent to about 400 milligrams of caffeine) a day had a 50% lower risk of suicide than adults who drank decaffeinated coffee or less than one cup of caffeinated coffee. Drinking more than four cups of coffee a day did not further reduce the risk of suicide.

Like all relevant results, it is worth noting that the analysis did not show a causal relationship between coffee drinking and a reduced risk of suicide, and there is no evidence in this study that a sudden and significant increase in your caffeine intake relieves depression. It is also worth noting that the three studies investigated in this study are all cohort studies, which means that these studies track multiple health risk factors in large clusters over a period of several years. It can be surprisingly difficult to control multiple variables. Statisticians do not often use the results of group studies.

That said, the neurochemical analysis behind the discovery makes some sense. The effect of caffeine is similar to a chemical called adenosine found in the brain and other parts of the body. Adenosine is produced by neurons and restricts balance; the more adenosine is produced, the less active the nervous system is until we finally fall asleep and rejuvenate.

Acting like adenosine, caffeine blocks receptors in the nervous system from receiving signals that reduce energy consumption. When this happens, levels of neurostimulants-dopamine and glutamate-rise in the brain, and we experience the stimulating effects of drinking a large cup of Java coffee.

In this respect, coffee may act like a mild antidepressant, at least to some extent. Previous studies have found similar correlations, further suggesting that coffee, the world's most frequently ingested psychoactive substance, can help ease the likelihood of depression.

However, this study must be treated cautiously, and its results are by no means conclusive. Given the shortcomings of the group study, the latest findings are likely to be an "illusion", and outside this particular study, the correlation is likely to be untenable.