Many things can trigger depression. It is common during life changes such as adolescence, marriage, birth and menopause. It can be a consequence of your upbringing - such as whether or not you were taught effective coping skills as a child. There is a genetic component to depression, and influences such as diet, stress and illness also play a part.

Being depressed can make you feel out of control and helpless, yet there are many ways to avoid falling into depression.

* Examine your diet. What you eat - or don’t eat - can influence your mood. The same diets that can cause heart disease and arthritis in some individuals - one that is high in sodium and saturated fat, and low in whole, fresh plant foods and unrefined essential fatty acids (EFAs) - can cause depression in others. Likewise, food allergies can also alter brain function and trigger depression (Biol Psychiatry, 1981; 16: 3-19). Wheat, milk, corn, beef and eggs are common culprits (Ann Allergy, 1982; 48: 166-71). But bear in mind that food allergies linked to depression often have an addictive quality - so whatever you eat compulsively may be contributing to the problem.

* Psychotherapy is as effective as drugs. Cognitive behavioural therapy can help those at risk of depression to become more conscious of negative thoughts and attitudes that feed into their depressions. Patients undergoing such therapy can learn to change (or at least mitigate) these unhelpful tendencies (J Consult Clin Psychol, 1989; 57: 414-9).

* Drug-induced depression is very common. Around 200 different classes of drugs have been implicated, including beta-blockers, tranquillisers, corticosteroids and birth-control pills, as well as alcohol and recreational drugs. If you think you may be reacting to a drug, consider switching to another family of drugs or trying other options.

* Environmental pollutants such as heavy metals, petrochemicals, pesticides and other toxins can disrupt the nervous system and lead to mild, but chronic, mood disorders, including depression (Med Clin North Am, 1990; 74: 325-45). Similarly, exposure to electromagnetic fields (EMFs), especially at work (West J Med, 2000; 173: 94-100) can lead to more depression and suicide in some vulnerable individuals (Bioelectromagnetics, 2001; [Suppl 5]: S132-43).

* St John’s wort is the most effective herbal remedy for mild depression because it works in a similar way to conventional antidepressants. A standardised extract (0.03 per cent hypericin) usually at a dose of 300 mg three times a day can be just as effective as antidepressant drugs (BMJ, 1996; 313: 253-8). What’s more, the side-effects are minimal.

* Traditional acupuncture can be as good as conventional drugs for preventing relapses in depression (Compl Ther Med, 2001; 9: 216-8).

* Electroacupuncture can benefit those suffering from major depression who cannot tolerate the side-effects of antidepressant drugs (Psychiatry Clin Neurosci, 1998; 52 [Suppl]: S338-40).

* Stay active. People who exercise regularly have less depression (Prev Med, 2003; 36: 698- 703). Typically, any aerobic exercise, such as walking or jogging, for 20-30 minutes three or four times a week will benefit mild-to-moderate depression (BMJ, 1985; 291: 109).

* Acknowledge your feelings. Depressed individuals often try to suppress their ‘bad’ feelings, especially those concerning distressing life experiences. ‘Confessing’ your most troubling feelings and experiences in a private diary can have significant long-term benefits on both mental and physical health (J Abnorm Psychol, 1986; 95: 274-81; J Consult Clin Psychol, 1989; 57: 414-9).

* Get a good night’s sleep. Since depression and lack of sleep can form a vicious circle, make sure you sleep well. Stick to regular bedtimes; having curtains that keep the light out will help regulate night-time melatonin secretion; and don’t exercise or take stimulants such as coffee or alcohol before going to bed.