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Effects of Nutrients (in Food) on the Structure and Function of the Nervous System: Update on Dietary Requirements for Brain. Part 1: Micronutrients. 2006

The objective of this update is to give an overview of the effects of dietary nutrients on the structure and certain functions of the brain. As any other organ, the brain is elaborated from substances present in the diet (sometimes exclusively, for vitamins, minerals, essential amino-acids and essential fatty acids, including omega- 3 polyunsaturated fatty acids). However, for long it was not fully accepted that food can have an influence on brain structure, and thus on its function, including cognitive and intellectuals. In fact, most micronutrients (vitamins and trace-elements) have been directly evaluated in the setting of cerebral functioning. For instance, to produce energy, the use of glucose by nervous tissue implies the presence of vitamin B1; this vitamin modulates cognitive performance, especially in the elderly. Vitamin B9 preserves brain during its development and memory during ageing. Vitamin B6 is likely to benefit in treating premenstrual depression. Vitamins B6 and B12, among others, are directly involved in the synthesis of some neurotransmitters. Vitamin B12 delays the onset of signs of dementia (and blood abnormalities), provided it is administered in a precise clinical timing window, before the onset of the first symptoms. Supplementation with cobalamin improves cerebral and cognitive functions in the elderly; it frequently improves the functioning of factors related to the frontal lobe, as well as the language function of those with cognitive disorders. Adolescents who have a borderline level of vitamin B12 develop signs of cognitive changes. In the brain, the nerve endings contain the highest concentrations of vitamin C in the human body (after the suprarenal glands). Vitamin D (or certain of its analogues) could be of interest in the prevention of various aspects of neurodegenerative or neuroimmune diseases. Among the various vitamin E components (tocopherols and tocotrienols), only alpha-tocopherol is actively uptaken by the brain and is directly involved in nervous membranes protection. Even vitamin K has been involved in nervous tissue biochemistry. Iron is necessary to ensure oxygenation and to produce energy in the cerebral parenchyma (via cytochrome oxidase), and for the synthesis of neurotransmitters and myelin; iron deficiency is found in children with attention-deficit/hyperactivity disorder. Iron concentrations in the umbilical artery are critical during the development of the foetus, and in relation with the IQ in the child; infantile anaemia with its associated iron deficiency is linked to perturbation of the development of cognitive functions. Iron deficiency anaemia is common, particularly in women, and is associated, for instance, with apathy, depression and rapid fatigue when exercising. Lithium importance, at least in psychiatry, is known for a long time. Magnesium plays important roles in all the major metabolisms: in oxidation-reduction and in ionic regulation, among others. Zinc participates among others in the perception of taste. An unbalanced copper metabolism homeostasis (due to dietary deficiency) could be linked to Alzheimer disease. The iodine provided by the thyroid hormone ensures the energy metabolism of the cerebral cells; the dietary reduction of iodine during pregnancy induces severe cerebral dysfunction, actually leading to cretinism. Among many mechanisms, manganese, copper, and zinc participate in enzymatic mechanisms that protect against free radicals, toxic derivatives of oxygen. More specifically, the full genetic potential of the child for physical growth ad mental development may be compromised due to deficiency (even subclinical) of micronutrients. Children and adolescents with poor nutritional status are exposed to alterations of mental and behavioural functions that can be corrected by dietary measures, but only to certain extend. Indeed, nutrient composition and meal pattern can exert either immediate or long-term effects, beneficial or adverse. Brain diseases during aging can also be due to failure for protective mechanism, due to dietary deficiencies, for instance in anti-oxidants and nutrients (trace elements, vitamins, non essential micronutrients such as polyphenols) related with protection against free radicals. Macronutrients are presented in the accompanying paper.
PMID: 17066209

Effects of Nutrients (in Food) on the Structure and Function of the Nervous System: Update on Dietary Requirements for Brain. Part 2 : Macronutrients. 2006

Among polyunsaturated omega-3 fatty acids, ALA (alpha-linolenic acid) provided the first coherent multidisciplinary experimental demonstration of the effect of diet (one of its major macronutrient) on the structure, the biochemistry, the physiology and thus the function of the brain. In fact, DHA (docosahexaenoic acid) is one for the major building structures of membrane phospholipids of brain and absolute necessary of neuronal function. It was first demonstrated that the differentiation and functioning of cultured brain cells requires not only ALA, but also the very long polyunsaturated omega-3 (DHA) and omega-6 carbon chains. Then, it was found that ALA acid deficiency alters the course of brain development, perturbs the composition of brain cell membranes, neurones, oligodendrocytes and astrocytes, as well as sub cellular particles such as myelin, nerve endings (synaptosomes) and mitochondria. These alterations induce physicochemical modifications in membranes, lead to biochemical and physiological perturbations, and results in neurosensory and behavioural upset. Consequently, the nature of polyunsaturated fatty acids (in particular omega-3, ALA and DHA) present in formula milks for infants (premature and term) conditions the visual, neurological and cerebral abilities, including intellectual. Dietary omega-3 fatty acids are involved in the prevention of some aspects of ischemic cardiovascular disease (including at the level of cerebral vascularization), and in some neuropsychiatric disorders, particularly depression, as well as in dementia, including Alzheimer's disease and vascular dementia. The implication of omega-3 fatty acids in major depression and bipolar disorder (manic-depressive illness) is under evaluation. Their dietary deficiency (and altered hepatic metabolism) can prevent the renewal of membranes and consequently accelerate cerebral ageing; nonetheless, the respective roles of the vascular component on one hand and the cerebral parenchyma itself on the other have not yet been clearly elucidated. Low fat diet may have adverse effects on mood. The nature of the amino acid composition of dietary proteins contributes to cerebral function; taking into account that tryptophan plays a special role. In fact, some indispensable amino acids present in dietary proteins participate to elaborate neurotransmitters (and neuromodulators). The regulation of glycaemia (thanks to the ingestion of food with a low glycaemic index ensuring a low insulin level) improves the quality and duration of intellectual performance, if only because at rest the brain consumes more than 50% of dietary carbohydrates, approximately 80% of which are used only for energy purpose. In infants, adults and aged, as well as in diabetes, poorer glycaemic control is associated with lower performances, for instance on tests of memory. At all ages, and more specifically in aged people, some cognitive functions appear sensitive to short term variations in glucose availability. The presence of dietary fibbers is associated with higher alertness ratings and ensures less perceived stress. Although an increasing number of genetic factors that may affect the risk of neurodegenerative disorders are being identified, number of findings show that dietary factors play major roles in determining whether the brain age successfully of experiences neurodegenerative disorders. Effects of micronutrients have been examined in the accompanying paper.
PMID: 17066210