• National Dementia Conference 2018

Dietary Determinants of Dementia

By Brendan Hutchinson
Bachelor of Science in Psychology
University of Canberra

Discuss the following statement providing evidence for nutrition-related factors associated with the development of dementia and translate this evidence into prevention strategies for the disease: “Dementia is a mental health disorder that is common in the elderly and has been associated with poor nutritional status”.

The layman will often consider both mental and nutritional health as mutually exclusive. Dementia is a disease of the mind and is characterised by a decrease in cognitive functioning. It is poorly understood, and yet it prevails across millions of individuals, most common to the elderly. Contemporary research has shown a far more prominent link between mental and nutritional health than was once presumed. An increasing amount of epidemiological research among varying populations suggests a strong association between many nutrition-related factors and dementia. The inference can be made from research that both vascular and oxidative pathways are relatively interrelated in the pathology of dementia. The vascular hypothesis suggests nutritional disorders such as obesity, diabetes and dyslipidemia all have dementia-related outcomes. Research supports the role of all three and places emphasis on middle age as a critical period for weight management in the development of dementia. The role of diet has also been well established. Research into the Mediterranean diet shows strong support that nutrient regulation can help prevent dementia. This diet includes unsaturated fatty acids, fruits and vegetables. Key nutrients have also been identified as having a protective role, such as the antioxidant vitamin E. The methodological plurality of evidence is sound, as support has been shown in varying research paradigms. Relevant preventative strategies will then be discussed. If implemented, they are likely to help raise awareness of the relationship between diet and dementia, and ultimately aid in reducing its worldwide prevalence. To begin, vascular pathology as rooted in malnutrition need be understood.

Recent research has accumulated suggesting the aetiology of dementia to be rooted in vascular pathology. Based on the vascular hypothesis, nutritional pathology may moderate vascular health and result in the development of dementia [1]. Vascular risk factors have been identified including stroke, high systolic blood pressure, low diastolic blood pressure, and heart failure [1]. A plethora of research has found links between dementia and various nutrition-related conditions such as obesity, diabetes, and dyslipidemia. For example, obesity has been directly associated with the deterioration of cognitive functioning [2]. In a cohort study on middle-aged US men and women, obesity was shown to increase the risk of dementia by up to 74%, while being overweight increased the risk up to 35% (P = 0.01) [3]. In a longitudinal study among over 3000 middle-age men, skin fold thickness (a popular measure of body fat estimation) was shown to increase the risk of dementia by upwards of 50% [4]. The study controlled for age, race, sex, education, and marital status, and this effect was only enhanced after controlling for co-morbid conditions. A meta-analysis by Beydoun et al [5] revealed a U-shaped relationship between body mass index (BMI) and cognitive decline; in middle age, a BMI that is either excessively low (underweight) or high (overweight) is a risk factor for developing dementia later in life [6]. This pattern was found to be significant even after controlling for socio-demographic variables and other health-related comorbidities [5]. Follow-up studies have found this relationship to be inversed in old age; a reduction in BMI may indicate the onset of dementia, while an increase in BMI may protect against it [6]. When baseline age was below 60 years the relationship between obesity and dementia was stronger, and was enhanced as the time period of the study increased [5]. While complex, this relationship provides support for the importance of body weight maintenance in maintaining healthy cognitive functioning. Indeed, controlling for these may help prevent or postpone dementia [6]. However, further research complicates the matter.

Investigations have found insulin resistance to explain a significant portion of the relationship between cognitive performance and obesity in adults over the age of 70 [2]. Insulin resistance is a dysfunction of body cells in responding to the hormone insulin, and primarily occurs in diabetes [7]. Several longitudinal studies have reported an association between diabetes and dementia [6]. This effect was strongest in middle age, although borderline diabetes and impaired glucose tolerance increased risk of dementia in old age [6]. One nine-year-long prospective study on elderly Catholics found that after adjusting for age, sex, and education, type 2 diabetes increased the risk of cognitive decline by 65% (P = 0.06) [8]. Further evidence comes from a longitudinal study on the elderly, showing a significant interaction between hypertension and diabetes, both of which predicted cognitive decline (P < 0.05) [9]. Finally, a study by Yaffe et al [10] showed that women with impaired fasting glucose were at twice the risk of developing dementia. There are several potential pathways by which diabetes may have this effect. These include oxidative stress, neuronal degeneration through hyperglycaemia, or alternatively due to co-morbid diseases such as dyslipidemia [6]. Dyslipidemia is an abnormal amount of lipids in the blood, and may result from prolonged elevation of insulin levels [11]. Dyslipidemia in the elderly has been linked to an increased risk of dementia and other cognitive impairments [12]. An increase in blood lipids may result in blood brain barrier impairment, therefore taxing the brain’s uptake of key micro nutrients like the antioxidant vitamin E [2,13]. In fact, antioxidants may be key in understanding the diet-disease relationship.

Antioxidant nutrients may have an important role in the prevention of dementia by protecting neuronal tissue from oxidative damage. Oxidative stress is widely considered an inherent physiological pathway for the development of dementia [6,14]. Antioxidant micro nutrients include carotenoids, flavonoids, vitamin C and vitamin E [14]. Among these, vitamin E is the most prevailing fat soluble vitamin to be used by the brain [13]. Several studies have reported a decrease risk of dementia after increasing intake of vitamins E and C [6]. Indeed, plasma levels of antioxidant micronutrients have been shown to be reduced in sufferers of dementia [6]. For example, Helmer et al [15] found reduced plasma levels of vitamin E was associated with an increased risk of dementia. One of the functions of epidemiological research is to search for patterns within specified populations and trace those to disease outcomes. Epidemiological studies have consistently found an inverse relationship between dietary vitamin E intake and dementia [14]. In a randomised clinical trial, vitamin E supplementation was found to have a significant effect on the rate of cognitive decline in women with low dietary intake at baseline [14]. Other antioxidants have also been found to be important; Supplementation of b-carotene over an 18-year period was shown to significantly reduce cognitive decline and the risk of dementia [14]. A longitudinal study by Devore et al [16] on nurse health also found carotenoids to potentially benefit cognition in the elderly over the age of 70. Of course, antioxidants need to be considered as part of the wider scope of a nutritionally sound diet. One diet in particular has great support for its protection against dementia.

Several epidemiological studies have shown a specific dietary pattern commonly referred to as the Mediterranean diet to be associated with the prevention of the most common form of dementia known as Alzheimer’s disease [1]. Common to countries such as Spain, Greece, and Turkey, it is often considered a standard for healthy eating [17]. The distinctive features of the Mediterranean diet include a large consumption of unsaturated fatty acids primarily from fish and olive oil, plenty of fruits and vegetables, cereals, and legumes [18]. The diet also consists of a low intake of red meat and wine [2,17]. Scarmeas et al [19-21] conducted several longitudinal studies over different populations in those aged 60 years or over. Patterns of findings consistently indicate that the Mediterranean diet is associated with a reduced risk of developing Alzheimer’s disease, cognitive functioning impairment, and a reduced risk of mortality in those with Alzheimer’s disease. Several key markers of the Mediterranean diet have been studied independent of one another and found to reduce the risk of cognitive decline and dementia. These include fish consumption, light to moderate alcohol use, and both monounsaturated and polyunsaturated fatty acids [14,17, 22]. However, the analysis of single nutrients ignores important interactions between dietary components. Clearly, adherence to the Mediterranean diet appears to protect against dementia. An explanation may be found in a reduced risk of developing vascular diseases associated with dementia such as coronary artery disease and hypertension [17]. Alternatively, the Mediterranean diet may aid in gene regulation during proposed critical developmental periods of dementia [17]. Regardless, the finding that a specific diet may have a protective role against dementia is extremely important when considering preventative strategies, as it allows us to infer general guidelines that need be met.

Research findings indicate the pathways between diet and dementia are complex and therefore several nutritional guidelines need be implemented. Currently, there is no attempt at identifying suspected risk factors of dementia in a cognitively healthy population [17]. Therefore, strategies aimed at preventing dementia are of utmost importance. To begin, we must emphasise the importance of long-term nutritional goals; The Latent Early-Life Association Regulation model suggests that dietary patterns may alter gene regulation during early life periods that results in pathology later in life [17]. This highlights the importance of viewing nutritional goals as a lifelong process. However, awareness that middle age could be a critical period for the onset of dementia should be promoted. The importance of diet need be made exceptionally clear during this developmental period. To better maintain healthy weight within the population, a preventative measure must entail an alteration of currently implemented dietary guidelines. First, there must be a greater emphasis on the energy content of individual foods. This can be done by clearly labelling every food packaging with its energy content. Also, the average energy content in popular food items that generally remain within a fixed energy limit (ie fruits, cereals) should be more easily accessible (eg through posters in supermarkets, advertised on TV, and given through dietary guidelines such as the Australian Guide to Healthy Eating). This should then be combined with promoting a better understanding of individual energy requirements. This can be done through promoting online energy calculators. While no calculator will be completely accurate, they are generally easy to use, readily accessible, and will give some point of reference to the individual’s energy needs. A greater amount of physical activity has been associated with reduced risk of dementia [5], and appears to have benefits in global functioning [12]. Therefore, these dietary strategies should be combined with physical activity and promotion of regular exercise. Physical activity will also help in the prevention of obesity and maintenance of a healthy weight. Finally, nutritional guidelines should include recommendations of eating a diverse diet that includes fish, unsaturated fatty acids, fruits, vegetables, nuts, legumes, and foods high in vitamin E (ie nuts, olives, spinach).

Dementia is characterised by a decline in cognitive capacity. There is clearly strong evidence supporting the role of nutritional-related factors. Obesity, diabetes, and dyslipidemia have all been linked to the onset of cognitive decline. This has been shown to come about through various pathways. Dietary patterns that encompass higher intake of unsaturated fatty acids, fruits and vegetables, nuts, legume, and antioxidant nutrients appear to protect against dementia. Middle age appears to be an important period of time, when special care must be given to maintain a healthy body weight range. Sustaining or even increasing body weight may be important as age increases, as a reduction in weight may indicate onset of dementia. The preventative strategy proposed is multifaceted. A deeper understanding of individual energy requirements and energy contents of foods need be promoted. Relevant dietary guidelines should be updated to place emphasis on foods rich in unsaturated fatty acids and vitamin E. While the aetiology of dementia is not completely understood, it seems clear that diet must play a role. This does not mean there is reason to panic. Instead, this is more a reason to abide by the basic healthy lifestyle choices that have been recommended for some time: maintaining a healthy weight, partaking in exercise, and consuming a diverse diet filled with plenty of unsaturated fats, fruits and vegetables.

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