Cognitive decline is a common disorder associated with ageing, with a prevalence of between 5 to 30%. Effective strategies to prevent cognitive decline involving nutrition have centred around the use of B vitamins, following evidence that some B vitamin may be beneficial at improving aspects of memory. The association between B vitamin status and memory may be due to the high energy requirements of neuronal tissues. Such tissues would be particularly sensitive to low levels of certain B vitamins that act as co-factors in the energy production pathways. However, it is known that high levels of homocysteine can damage the endothelial lining of blood vessels, leading to atherosclerosis and a possible reduction in blood flow to brain tissue. The requirement of folate, cobalamin and pyridoxal phosphate in the normal metabolism of homocysteine may explain their benefit some in cases of memory decline.
Because of the possible involvement of some B vitamins in preventing cognitive decline, researchers are interested in investigating the effects of supplementation on elderly individuals. For example, one study published in the American Journal of Clinical Nutrition1 administered 400µg of folic acid with 100µg of vitamin B12, or a placebo, to assess their effects on depressive symptoms in a randomised controlled trial. The 900 subjects involved in the trial were all between 60 and 74 years with elevated psychological distress. Changes in cognition were examined in telephone interviews. The authors reported that folic acid plus vitamin B12 supplements improved recall from a telephone interview at 24 months when compared to the placebo. However, tests of orientation, attention, semantic memory, processing speed or informant reports were not improved. Plasma concentrations of folate and B12 increased significantly by 66.0% (573 to 951nmol/L) and 55.7% (305 to 475nmol/L), respectively.
These results support previous research suggesting that folic acid and vitamin B12 may be useful in the prevention of cognitive decline in elderly subjects. The mechanisms for this action is unknown, but may involve reductions in homocysteine levels or improvements in neuronal energy production. interestingly, in this study homocysteine plasma levels were not reduced by the supplements (homocysteine rose 8.33% in the treatment group compared to 22.5% in the placebo group), suggesting that reductions in plasma homocysteine levels were not the reasons for the improvement in memory. The weight of evidence also suggests that these vitamins do not work in a drug-like manner. More likely, B vitamin supplements reverse chronic deficiencies, caused by a deterioration in food quality and a reduction in absorption, associated with ageing. Folate and vitamin B12 may therefore benefit cognition through mechanisms other than homocysteine lowering.
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