Through summarizing the earlier studies, we found a significant association between the dietary intake of elderly people and their oral health; however, some investigators had failed to find this relationship. Several studies had demonstrated that there was an association between destroyed dentition and malnutrition within the past ten years.[29
] However, many of these studies had not considered the confounding role of the common risk factors of malnutrition in evaluating this association. Most of these studies had measured the nutritional status using inaccurate methods causing a bias in assessing the relationship between the dental and nutritional status.
A recent study[36
] adjusted the common risk factors affecting nutritional status and found that poor dental status was still related to malnutrition in elderly individuals and showed that decreased masticatory performance could increase the possibility of malnutrition; however, Mojon et al
] and Nordenram et al
] concluded that only highly impaired dentition was related to malnutrition among the elderly population.
Liedberg et al
] found no significant difference with respect to the number of teeth and inadequate nutrient intake, which was not in agreement with the finding of Marshal et al
] stating that adequate intake of calcium and folate was observed only in individuals with adequate number of teeth. However, inaccurate tests used to measure oral status and nutrient adequacy could cause a bias in making a direct comparison of studies. de Andrade et al
] showed that the number of posterior occluding pairs was the strongest predictor of a higher risk of malnutrition among three parameters of oral health. However, almost all studies using objective clinical variables, including the number of teeth, tooth distribution, number of occluding natural pairs, tooth condition or duration, and the number of chewing strokes before swallowing, concluded that there is a relationship between oral health status and food intake.[19
] Conversely, Daly et al
] found no association between these two variables in a small sample of the elderly, but the oral health status was not always consistent with the objective clinical data. A large number of cross-sectional and longitudinal studies done in Europe and the USA[19
] supported this assumption that there was a significant association between the oral health and food intake, and this association was independent of the demographic factors such as age.[45
] Inadequate intake of vitamins A, C, and B6
could cause visual, immunological, and cardiovascular disorders.[46
] Other studies had contributed to gastritis and peptic ulcers and to oral health problems, such as, impaired chewing or increased gastric acidity.[47
] According to the literature there was an inverse relation between masticatory efficiency and cholesterol intake, which meant that masticatory deficiency was an indirect risk factor for cardiovascular disease, with serious outcomes.[48
] However, further research is needed, to explore whether oral health problems are a cause or a result of these systemic diseases.
Saliva acts as a lubricant in the masticatory process[51
] and oral dryness has an important role in food choice and oral manipulation of food, which is even greater than the role of masticatory efficiency.[52
] The three main causes of xerostomia in elderly individuals include: dehydration, salivary gland deterioration, and neural transmissions interfering with salivary secretion.[53
] As salivary secretion is provoked by a normal masticatory function, decreased masticatory function may lead to salivary gland atrophy, and therefore, decreased synthesis and secretion of saliva.[54
] Even though there are numerous studies linking masticatory function and inadequate food intake, none of them established a causal relationship. Shinkai et al
] have concluded that differences in masticatory variables between all dentition groups do not affect the diet pattern, which shows the ability to compensate the reduced masticatory function among patients with impaired dentition.
Furthermore, longitudinal-cohort studies considering the role of confounding variables such as coffee or tea drinking, smoking, aging, socioeconomic status, and psychological status affecting the nutritional status, with a larger sample size, are required to better investigate the profound interactions between dental status and dietary intake. It must be acknowledged that caries and periodontal disease, which are the main causes of tooth loss, are of high prevalence among elderly individuals and both are preventable. The majority of the public health policy's focus for preventive oral health care and dietary intake modifications should be given to the elderly population because of a high prevalence of tooth loss and nutrient deficiency within this population.
The public health promotion's efforts should be developed to make the elderly individuals aware of the essential role of functional dentition on food choice and masticatory performance.
Finally, it should be noted that this review provides the background knowledge for the oral health track of the ‘Study on the Epidemiology of Psychological, Alimentary Health, and Nutrition’ (SEPAHAN).[56