ABSTRACT
The association between nutrition and cognitive performance has become a topic of increasing scientific and public interest.1 Nutrition may be an important, modifiable, life-style factor in age-related cognitive decline and there is a growing interest in the development of nutritional supplements as therapeutic agents aimed at enhancing or maintaining cognitive function or delaying cognitive decline.2 The role that food and nutrition has in the course of age-related cognitive change is yet to be clearly defined. However, early findings from epidemiological and experimental studies suggest that there may be a role for dietary components such as: folate and vitamins B-12 and B-6, antioxidants, omega 3 fatty acids, and herbal supplements like Ginkgo biloba. The assumption that food and its components can impact on cognitive performance and age-related cognitive change is based on the knowledge that the central nervous system (CNS) depends heavily for efficient functioning on a constant supply of almost all of the essential nutrients as well as glucose and oxygen.3 If brain function is optimised, one would expect cognitive function to be optimised as well. Understanding this link between brain function and cognitive function is important in the formulation of hypotheses about diet-cognition links and how we might test them. We need to base research in the area of diet and cognition on hypotheses about the mechanisms by which nutrients or other aspects of the diet might impact on the brain, and how this in turn affects cognitive performance. Nutrients may impact on the brain in
a number of ways such as: on neurotransmitter synthesis, on the structure of neurons, and on the vasculature of the brain. The effects of nutrients on the brain may be short-term and acute, or more longer-term due to dietary habits over an extended period of time. Importantly, if we understand the mechanisms by which nutrients affect the brain, we can more accurately predict the role that nutrients may have in cognitive ageing and which aspects of cognition are likely to be affected by nutritional factors. At a very basic level, we might expect nutritional factors to impact on fluid, rather than crystallised, abilities among older adults.4 Fluid ability is thought to reflect innate information processing that is determined by genetic and physiological factors such as the integrity of the CNS. Fluid ability is demonstrated in the capacity to process novel information, that is, to apply mental processes to situations that require no previous knowledge. Crystallised ability refers to the application of learned information and cultural experience acquired over the lifetime and therefore depends on our store of knowledge, education and cultural background. Due to its reliance on the integrity of the CNS, we might expect nutritional factors to have more of an impact on fluid, rather than crystallised, ability. Furthermore, there are some aspects of cognition that show marked agerelated decline, such as memory performance and cognitive resources, that may also be sensitive to nutritional factors. Cognitive resources refer to our mental capacity to perform cognitive tasks. The three identified cognitive resources are: speed of information processing (how fast we can think); working memory capacity (how much information we can simultaneously store and work on); and attentional capacity (how long we can concentrate for). Because these resources are so important for the efficient working of the cognitive system,5 any investigation of the links between nutrition and cognitive performance should include measures of cognitive resources.4 In summary, because cognition is multidimensional, it is crucial that pertinent tests of cognitive performance be selected in order to test hypotheses that specify the impact that nutritional factors might have on the cognitive system.
