Acides gras ω-3 et troubles psychiatriques Omega-3 fatty acids in psychiatry

Résumé

Les acides gras ω-3 ont été parmi les premiers nutriments dont un effet sur la structure et la fonction du cerveau a été démontré. L’exceptionnelle richesse de cet organe en acides gras ω-3 explique, au moins en partie, l’étude de l’influence des apports alimentaires en ces nutriments sur certaines maladies psychiatriques et sur le déclin cognitif lié au vieillissement. Au final, les acides gras ω-3 semblent efficaces dans la prévention du stress, de la dépression et de la démence, notamment au cours de la maladie d’Alzheimer. Si leur rôle comme régulateur de l’humeur demeure hypothétique, ils pourraient être impliqués dans la dépression, notamment celle du post-partum, et dans le trouble bipolaire. Enfin, le rôle des acides gras ω-3 alimentaires dans l’autisme et la schizophrénie doit encore être démontré. Les relations établies entre ces apports alimentaires et certains troubles mentaux justifient que l’on se préoccupe de l’insuffisance en acides gras ω-3 dans le régime de la population française (moins de 50 % des apports conseillés pour l’acide α-linolénique), d’autant que ce déficit pourrait être facilement résorbé, notamment par la consommation d’huile de colza.

Summary

The brain is one of the organs with the highest level of lipids (fats). Brain lipids, formed of fatty acids, participate in the structure of membranes, for instance 50 % fatty acids are polyunsaturated in the gray matter, 1/3 are of the omega-3 family, and are thus of dietary origin. The omega-3 fatty acids (mainly alpha-linolenic acid, ALA) participated in one of the first experimental demonstration of the effect of dietary substances (nutrients) on the structure and function of the brain. Experiments were first of all carried out on ex vivo cultured brain cells, then on in vivo brain cells (neurons, astrocytes and oligodendrocytes) from animals fed ALA deficient diet, finally on physicochemical (membrane fluidity), biochemical, physiological, neurosensory (vision an auditory responses), and behavioural or learning parameters. These findings indicated that the nature of polyunsaturated fatty acids (in particular omega-3) present in formula milks for human infants determines to a certain extend the visual, neurological, and intellectual abilities. Thus, in view of these results and of the high polyunsaturated fatty acid content of the brain, it is normal to consider that they could be involved in psychiatric diseases and in the cognitive decline of ageing. Omega-3 fatty acids appear effective in the prevention of stress, however their role as regulator of mood is a matter for discussion. Indeed, they play a role in the prevention of some disorders including depression (especially post partum), as well as in dementia, particularly Alzheimer’s disease. Their role in major depression and bipolar disorder (manic-depressive disease), only poorly documented, is not clearly demonstrated. The intervention of omega-3 in dyslexia, autism, and schizophrenia has been suggested, but it does not necessarily infer a nutritional problems. The respective importance of the vascular system (where the omega-3 are actually active) and the cerebral parenchyma itself, remain to be resolved. However, the insufficient supply of omega-3 fatty acids in today diet in occidental (less than 50 % of the recommended dietary intakes values for ALA) raises the problem of how to correct inadequate dietary habits, by prescribing mainly rapeseed (canola) and walnut oils on the one hand, fatty fish (wild, or farmed, but the nature of fatty acids present in fish flesh is the direct consequence of the nature of fats with which they have been fed), and eggs from laying hens fed omega-3 fatty acids.