Nerve tissue possesses the highest concentration of fatty acids after adipose tissue. The long chain fatty acids (omega-3 and omega-6) provided in food are essential for the structure and function of nerve cells.
A change to the level of essential fatty acids in synaptic membranes can affect neurone function, firstly by altering the way the receptor membranes, ion channels and enzymes function, and secondly by affecting the transmission of intra- and inter-cellular signals generated by secondary messengers, of which long-chain fatty acids are the precursors. Omega-3 essential fatty acids also directly influence the production and release of some neurotransmitters such as serotonin and dopamine.
In addition, for cultured nerve cells to differentiate themselves, multiply, and capture and release neuromediators, the medium must contain long-chain polyunsaturated fatty acids.
Omega-3 and depression: scientific data
Results from a scientific study suggest that omega-3 fatty acids promote transmission of the neurotransmitters associated with emotional stability (e.g. serotonin) and positive emotions (e.g. dopamine) (Chalon, Delion-Vancassel and al. 1998).
The existence of a link between depression and too low a level of omega-3 fatty acids in the body has been indicated in several scientific studies. For instance, two different studies concluded that depressed patients have lower reserves of omega-3 acids than normal subjects (Maes, Smith et al. 1996; Maes, Smith et al. 1998; Peet, Murphy et al. 1998).
Another study showed that the lower the reserves of omega-3 acids in patients, the more severe their symptoms (Adams, Lawson et al. 1996).
A fourth study showed that the richer the subjects' current diet in omega-3, the less tendency there was for them to become depressed (Edwards, Peet et al. 1998).
Extensive population surveys in Finland and Holland have tended to confirm that the higher their current diet in omega-3 fatty acids, the less people suffer from symptoms of depression (Tanskanen, Hibbeln et al., 2001; Tiemeier, van Tuijl et al. 2003).
At Harvard, Doctor Andrew Stoll was the first to show that emotional stability can be improved by adjusting the level of omega-3 fatty acids in nutritional intake. In a group of patients who all suffered from frequent and serious swings between depressive and manic episodes (bi-polar disorder, or manic-depression), treatment based on 9 grams per day of DHA and EPA combined in the ratio 1: 1.5, considerably reduced the incidence of mood swings. Among the group of patients in the study who took omega-3 acids, only one relapsed.
The results were so conclusive that the researchers had to stop the study after four months. Patients in the control group - who received only a placebo based on olive oil (which, although it has beneficial properties as an anti-oxidant, does not contain omega-3 acids) - relapsed so much more quickly than those in the omega-3 group that it would have been contrary to medical ethics to deprive them any longer (Stoll, Severus et al. 1999).
Since then, in Israel, Doctor Nemets and his staff have compared the effectiveness of purified fish-oil extract, ethyl-eicosapentaenoic acid (pure EPA) with an equivalent dose of olive oil in treating patients suffering from depression (with no manic episodes). The group of patients had relapsed into depression despite treatment with anti-depressants. Over half these patients experienced an overall improvement, with depressive symptoms reduced by 50% or more, in under three weeks (Nemets, Stahl et al. 2002).
Another study, this time in Britain, has been published in the Archives of General Psychiatry. It reached the same conclusion, and its results also suggest that omega-3 fatty acids improve the whole range of depressive symptoms: feelings of sadness and energy loss, anxiety and insomnia, loss of libido as well as suicidal tendencies (Peet and Horrobin 2002).
Finally, another study in a Harvard hospital has been published recently in the American Journal of Psychiatry. The subjects were women with difficult mood swings that complicated their emotional relationships and made them feel that their emotions were often "out of control". After eight weeks of treatment with an omega-3 supplement rich in EPA, they were in more positive spirits and they were overall less aggressive to their families and friends (Zanarini and Frankenburg 2003).
The relationship between EPA and DHA
|The studies suggest that it is EPA that promotes positive emotions, rather than DHA (Nemets, Stahl et al. 2002; Peet and Horrobin 2002). Studies using pure DHA have shown it has no more effect than a placebo (Marangell, Martinez et al. 2003). In addition, a competition mechanism means DHA prevents
EPA being completely assimilated and used (Horrobin, 2002), while by contrast, the body can transform EPA into DHA as required.