It is often assumed that cognitive decline is a normal part of ageing, and to some extent this is true. However, the decline if often exaggerated considerably by poor diet and Western lifestyle habits. Evidence from populations that eat high quality diets for their entire life, such as found in Sicily in Italy, do not show this decline and often remain fully cognitive efficient even into old age. The decline in cognitive ability seen in Western nations is termed mild cognitive decline, to distinguish it from the more serious dementias that can also develop. In fact, mild cognitive decline is considered to be transient in state between full cognitive efficiency and dementia. Dementia is characterised by an atrophy in the size of the brain, and this can be seen also in mild cognitive decline, although at a much slower rate. Decreasing the rate of the decline in brain size is therefore pivotal to preventing the ultimate deterioration into dementia seen with ageing. A number of nutritional strategies have been shown to aid this protective process.
Omega-3 fatty acids, particularly docosahexaenoic acid (DHA, C22:6 (n-3)) have been shown to be beneficial to the health of the brain, during both development, and ageing. The brain is made up of high amounts of lipids and the nature of the lipids supplied to the brain from structural integrity appears to dramatically affect the function of the brain. Supplying increased amounts of DHA, present in high concentrations in fish oils, can provide significant cognitive benefits. However, supplying just fish oils to the brain may not be the most effective way to provide cognitive benefits, as nutrient often interact and the metabolism of one nutrient may require accessory nutrients in order to be able to have beneficial effects. This interaction between nutrients was demonstrated clearly in a study that examined the effects of B vitamins on the brain atrophy in older individuals. Subjects were fed 0.8 mg folic acid, 20 mg vitamin B6 and 0.5 mg vitamin B12 and their plasma omega-3 fatty acid levels were assessed.
The supplementation lasted for 2 years and during this time an magnetic resonance imaging device was used to asses the size of the brain. The results of the study found that there was a significant interaction between the B vitamin and the omega-3 fatty acid content of the plasma. Subjects with omega-3 fatty acid levels above 590 μmol/L showed a significant 40 % reduction in the rate of brain atrophy compared to the placebo. However, in those subject with baseline levels of omega-3 fatty acids below 390μmol/L in their plasma, there was no significant effect on brain atrophy rates. These results suggest that the omega-3 fatty acids present in the subjects required B vitamins to have beneficial effects in the brain. The subjects may have been deficient in B vitamins and this may have prevented them utilising the omega-3 fatty acids. B vitamins also play an important role in energy metabolism, and act as cofactors in a number of enzymes. Neurons require high amounts of energy and so B vitamins are important to brain health.
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