Diet and dementia.

The ageing brain adapts to the accumulation of damage caused by oxidative stress and inflammation. Adaptive processes include neuroprotective and neurorestorative mechanisms. Individual differences in susceptibility to dementia arise when these mechanisms are impaired or are overwhelmed by the molecular pathology of Alzheimer's disease. Neuroprotection relies upon extrinsic and intrinsic defences. An adequate intake of antioxidant micronutrients (eg, vitamin C and vitamin E) and anti-inflammatory macronutrients (eg, omega-3 polyunsaturated fatty acids) forms an essential component of extrinsic defences against brain ageing. There are many epidemiological data to support an association between an inadequate intake of antioxidants and/or fish oils (an important source of omega-3 polyunsaturated fatty acids) and a greater than expected incidence of late onset dementia. These associations are confounded by established links between poverty, poor diet and failing health, especially in old age. Such links may be sufficient to explain some of the effects of an inadequate diet on the retention of cognitive function and increased risk of dementia in old age. More compelling is the association between increased plasma homocysteine concentration and later increased risk of dementia. This association is possibly caused by an inadequate intake of vitamin B(12)/folate.