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      N-of-1 Clinical Trials in Nutritional Interventions Directed at Improving Cognitive Function

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          Abstract

          Longer life expectancy has led to an increase in the prevalence of age-related cognitive decline and dementia worldwide. Due to the current lack of effective treatment for these conditions, preventive strategies represent a research priority. A large body of evidence suggests that nutrition is involved in the pathogenesis of age-related cognitive decline, but also that it may play a critical role in slowing down its progression. At a population level, healthy dietary patterns interventions, such as the Mediterranean and the MIND diets, have been associated with improved cognitive performance and a decreased risk of neurodegenerative disease development. In the era of evidence-based medicine and patient-centered healthcare, personalized nutritional recommendations would offer a considerable opportunity in preventing cognitive decline progression. N-of-1 clinical trials have emerged as a fundamental design in evidence-based medicine. They consider each individual as the only unit of observation and intervention. The aggregation of series of N-of-1 clinical trials also enables population-level conclusions. This review provides a general view of the current scientific evidence regarding nutrition and cognitive decline, and critically states its limitations when translating results into the clinical practice. Furthermore, we suggest methodological strategies to develop N-of-1 clinical trials focused on nutrition and cognition in an older population. Finally, we evaluate the potential challenges that researchers may face when performing studies in precision nutrition and cognition.

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          Dementia prevention, intervention, and care

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            A literature review on the representativeness of randomized controlled trial samples and implications for the external validity of trial results

            Randomized controlled trials (RCTs) are conducted under idealized and rigorously controlled conditions that may compromise their external validity. A literature review was conducted of published English language articles that reported the findings of studies assessing external validity by a comparison of the patient sample included in RCTs reporting on pharmaceutical interventions with patients from everyday clinical practice. The review focused on publications in the fields of cardiology, mental health, and oncology. A range of databases were interrogated (MEDLINE; EMBASE; Science Citation Index; Cochrane Methodology Register). Double-abstract review and data extraction were performed as per protocol specifications. Out of 5,456 de-duplicated abstracts, 52 studies met the inclusion criteria (cardiology, n = 20; mental health, n = 17; oncology, n = 15). Studies either performed an analysis of the baseline characteristics (demographic, socioeconomic, and clinical parameters) of RCT-enrolled patients compared with a real-world population, or assessed the proportion of real-world patients who would have been eligible for RCT inclusion following the application of RCT inclusion/exclusion criteria. Many of the included studies concluded that RCT samples are highly selected and have a lower risk profile than real-world populations, with the frequent exclusion of elderly patients and patients with co-morbidities. Calculation of ineligibility rates in individual studies showed that a high proportion of the general disease population was often excluded from trials. The majority of studies (n = 37 [71.2 %]) explicitly concluded that RCT samples were not broadly representative of real-world patients and that this may limit the external validity of the RCT. Authors made a number of recommendations to improve external validity. Findings from this review indicate that there is a need to improve the external validity of RCTs such that physicians treating patients in real-world settings have the appropriate evidence on which to base their clinical decisions. This goal could be achieved by trial design modification to include a more representative patient sample and by supplementing RCT evidence with data generated from observational studies. In general, a thoughtful approach to clinical evidence generation is required in which the trade-offs between internal and external validity are considered in a holistic and balanced manner. Electronic supplementary material The online version of this article (doi:10.1186/s13063-015-1023-4) contains supplementary material, which is available to authorized users.
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              Homocysteine, B Vitamins, and Cognitive Impairment.

              Moderately elevated plasma total homocysteine (tHcy) is a strong modifiable risk factor for vascular dementia and Alzheimer's disease. Prospectively, elevated tHcy is associated with cognitive decline, white matter damage, brain atrophy, neurofibrillary tangles, and dementia. Most homocysteine-lowering trials with folate and vitamins B6 and/or B12 tested as protective agents against cognitive decline were poorly designed by including subjects unlikely to benefit during the trial period. In contrast, trials in high-risk subjects, which have taken into account the baseline B vitamin status, show a slowing of cognitive decline and of atrophy in critical brain regions, results that are consistent with modification of the Alzheimer's disease process. Homocysteine may interact with both risk factors and protective factors, thereby identifying people at risk but also providing potential strategies for early intervention. Public health steps to slow cognitive decline should be promoted in individuals who are at risk of dementia, and more trials are needed to see if simple interventions with nutrients can prevent progression to dementia.
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                Author and article information

                Contributors
                Journal
                Front Nutr
                Front Nutr
                Front. Nutr.
                Frontiers in Nutrition
                Frontiers Media S.A.
                2296-861X
                23 July 2019
                2019
                : 6
                : 110
                Affiliations
                [1] 1Integrative Pharmacology and Systems Neurosciences Research Group, Neurosciences Research Program, Hospital del Mar Medical Research Institute (IMIM) , Barcelona, Spain
                [2] 2Department of Experimental and Health Sciences, University Pompeu Fabra , Barcelona, Spain
                [3] 3Department of Statistics and Operations Research, Universitat Politècnica de Barcelona/Barcelonatech , Barcelona, Spain
                [4] 4CIBER de Fisiopatología de la Obesidad y la Nutrición (CIBEROBN), Instituto de Salud Carlos III , Madrid, Spain
                Author notes

                Edited by: Yuanlong Pan, Nestlé R&D, United States

                Reviewed by: Esther Aarts, Radboud University Nijmegen, Netherlands; James William Simpkins, West Virginia University School of Medicine, United States; Jiong Shi, Barrow Neurological Institute (BNI), United States

                *Correspondence: Rafael de la Torre rtorre@ 123456imim.es

                This article was submitted to Neuroenergetics, Nutrition and Brain Health, a section of the journal Frontiers in Nutrition

                Article
                10.3389/fnut.2019.00110
                6663977
                31396517
                9a58c766-a654-4a44-9278-e0203e0a5281
                Copyright © 2019 Soldevila-Domenech, Boronat, Langohr and de la Torre.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                History
                : 26 November 2018
                : 08 July 2019
                Page count
                Figures: 3, Tables: 3, Equations: 0, References: 236, Pages: 20, Words: 17520
                Funding
                Funded by: Instituto de Salud Carlos III 10.13039/501100004587
                Categories
                Nutrition
                Review

                n-of-1,personalized nutrition,prevention,alzheimer's disease,multimodal interventions,cognition,cognitive decline

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