Dietary patterns for healthier cognitive ageing

<p>With ageing of our population and the accompanying increase in the number of people living with dementia, it is important to find modifiable risk factors to postpone the onset of cognitive decline. Diet has been proposed such a modifiable risk factor. To date, numerous studies have been conducted demonstrating a possible role of specific nutrients and foods in cognitive functioning. However, as people do not consume single nutrients, the research field has shifted towards studying dietary patterns in which synergistic effects of single nutrients and/or foods can be studied. The main aim of this thesis was to study the association of healthful dietary patterns with cognitive functioning. In addition, nutrient intake inadequacies were assessed and the potential to change dietary intake in older adults aged 65 years and older was studied.</p> <p><strong>Chapter 2</strong> describes nutrient intake of 245 Dutch adults aged 65-80 years. We identified the contribution of nutrient dense foods, fortified foods and dietary supplements to the total intake of micronutrients. Nutrient density of foods was evaluated using the Nutrient Rich Food score 9.3. Nutrient intake inadequacies were observed for vitamin D, vitamin B6 and selenium. Conventional foods were the main source of vitamin D, vitamin B6 and selenium intake. Foods with the highest nutrient density contributed most to total vitamin B6 intake. In order to optimize nutrient intakes of elderly, combinations of natural food sources, fortified foods and dietary supplements should be considered.</p> <p><strong>Chapter 3</strong> provides a systematic review of the literature on human studies up to May 2014 that examined the role of dietary patterns in relation to cognitive decline or dementia. The results demonstrate that better adherence to a Mediterranean diet was associated with less cognitive decline, dementia or Alzheimer’s Disease (AD) in four out of six cross-sectional studies, six out of 12 longitudinal studies, one trial and three meta-analyses. Other healthy dietary patterns, among which the Healthy Diet Indicator, have shown to be associated with reduced cognitive decline and/or a reduced risk of dementia in all six cross-sectional studies and six out of eight longitudinal studies. The conclusion of this literature review was that more conclusive evidence is needed to come to more targeted and detailed dietary guidelines to prevent or postpone cognitive decline.</p> <p>In <strong>chapter 4</strong> the association between the Healthy Diet Indicator (HDI) and cognitive functioning in older adults from three different cohort studies was investigated. The cohorts included in total 21,837 subjects from Europe (SENECA and the Rotterdam Study [RS]) and the Unites States (Nurses’ Health Study [NHS]). Cognitive functioning was measured using the Mini-Mental State Examination (MMSE) in SENECA and RS, and the Telephone Interview for Cognitive Status (TICS) in NHS. In all three cohorts, the HDI was not significantly associated with cognitive decline, nor with cognitive function.</p> <p>In <strong>chapter 5</strong> the association of long-term adherence to the Dietary Approaches to Stop Hypertension (DASH) diet with cognitive function and decline in older American women was examined. A total of 16,144 women from the Nurses’ Health Study, aged ≥70 years, who underwent cognitive testing a total of 4 times by telephone from 1995-2001 (baseline), with multiple dietary assessments between 1984 and the first cognitive exam were studied. Greater adherence to long-term DASH score was significantly associated with better average global cognition, verbal memory and TICS score at older ages, but not with cognitive decline.</p> <p>In<strong> chapter 6</strong>, the same cohort as in chapter 5 was studied to examine the association between long-term adherence to a recently developed Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet with cognitive function and decline. Higher MIND diet scores were associated with better verbal memory at older ages, but not with cognitive decline over 6 years in global cognition, verbal memory or TICS.</p> <p><strong>Chapter 7</strong> provides an overview of the NU-AGE (NUtrients and AGEing) dietary intervention study. The NU-AGE study is a randomized one-year intervention in 1,250 apparently healthy, independently living European subjects aged 65 to 80 years. Subjects were randomised into either the intervention group or the control group. Participants in the intervention group received dietary advice aimed at meeting the dietary recommendations of the ageing population. At the start of this thesis, the NU-AGE study was the first dietary intervention investigating the effect of a whole diet and providing targeted dietary recommendations for optimal health and quality of life in apparently healthy European elderly.</p> <p>In <strong>chapter 8</strong>, we evaluated if the NU-AGE intervention could be effective to shift the dietary intake of apparently healthy older adults aged 65-80 years living in Italy, the UK, the Netherlands, Poland, and France towards a more healthful diet. The NU-AGE index was created to assess adherence to the NU-AGE diet. At baseline and after one-year follow-up dietary intake was assessed by means of 7-day food records. In total, 1,296 participants were randomized and 1,145 participants completed the intervention (571 in intervention group, 570 in control group). After one-year follow-up, the intervention group improved mean intake of 13 out of 16 dietary recommendations of the NU-AGE diet (p&lt;0.05) with a significant increase of the total NU-AGE index, compared to the control group (mean change in NU-AGE index 21.3±15.9, p&lt;0.01). The NU-AGE dietary intervention, based on dietary recommendations for older adults, may be a feasible strategy to improve dietary intake in an ageing European population.</p> <p><strong>Chapter 9</strong> shows the results of the NU-AGE parallel randomized dietary intervention study on cognitive functioning in the Dutch NU-AGE subpopulation, including 252 older adults aged 65-80 years (123 intervention, 129 control). The primary outcome was one-year change in global cognition and in four cognitive domains as measured through a comprehensive neuropsychological test battery. Comparing the intervention with the control group, there was no effect of the intervention on cognitive functioning.</p> <p>In <strong>chapter 10</strong> the main findings of this thesis were summarized and a reflection on methodological aspects was given. When grading the reported associations in previous studies and studies in this thesis, it was concluded that there is <em>probable</em> evidence for a role of the Mediterranean diet on cognitive functioning. For the DASH and MIND diet there is a <em>possible</em> link with cognitive functioning; for the HDI and the NU-AGE diet there is <em>no sufficient</em> evidence yet to conclude that there is a relation with cognitive functioning. Not only is there a need for well-designed intervention and prospective studies, we also call for communication strategies to the general public about the consumption of healthier diets to not only impact cardiovascular but also potentially impact brain health as many individuals will face progressive cognitive decline in the near future.