Mastication for the mind

e goal of this literature review has been to investigate the relationship between mastication and cognition, with a special focus on ageing and dementia, and its possible underlying mechanisms. Since the relationship between mastication and cognition is not yet rmly established, and is investigated in the context of a number of di erent disciplines, a comprehensive overview will contribute to our knowledge. e results of animal and human experimental studies suggest a causal relationship between mastication and cognition. Furthermore, correlations exist between mastication and activities of daily living and nutritional status. ese ndings have compelling implications for the development of prevention strategies by which medical and nursing sta may optimize their care for the frail and elderly, su ering from dementia. is chapter has been published as: Weijenberg R.A., Scherder E.J., Lobbezoo F. – Mastication for the mind – e relationship between mastication and cognition in ageing and dementia. Neurosci.Biobehav.Rev. 35(3); 483–497, 2011. 16 • chapter 2 – mastication for the mind introduction e world population is ageing 1. For example, the senior population (persons over the age of 60) in developed regions will increase from 264 million in 2009 to 416 million in 2050 1. Given the fact that ageing is one of the risk factors for developing dementia 2, an increase in patients su ering from dementia is to be anticipated 3. ere are several risk factors for developing dementias like Alzheimer’s disease (AD), which is one of the most common subtypes of dementia 4. ese risk factors include ageing, illiteracy, a lower level of education, lower socioeconomic status 4, head trauma 5, genetic factors such as the apolipoprotein E4 (apoE4) allele 6, cardiovascular risk factors such as being overweight, smoking, hypertension and diabetes mellitus 7, an inactive lifestyle 8 and, perhaps surprisingly, loss of teeth 9,10. Loss of teeth has also been associated with malnutrition 11,12, mortality and disability 13, loss of cognitive function 14 and prevalence of dementia 12. is review will focus on the relationship between masticatory and cognitive function in ageing and dementia. e rst question we would like to answer is whether the literature supports the existence of such a relationship and whether this relationship is causal, i.e., does a deterioration of the masticatory system impair cognitive functioning in older persons with and without dementia? A related question concerns the mechanisms underlying this relationship. To our knowledge, neither question has been addressed before, which is why a literature search was performed. e literature on the relationship of mastication and cognition that will be addressed in this review will be subdivided into several categories: animal experimental studies, usually with a strong neuroanatomical focus; human experimental studies, with healthy (and typically young) subjects; and clinical studies, either cross-sectional or longitudinal, with a patient population su ering from either age-related or pathological loss of the ability to perform activities of daily living. Both physiological and behavioral changes will be discussed, where applicable.