By Micha Shalev
An estimated 5.3 million Americans of all ages have Alzheimer’s disease (AD), the most common type of dementia. Due to the increasing longevity of the U.S. population, the increasing incidence with age, and the lack of effective treatment options for AD, a dramatic rise in AD prevalence is expected. Thus, effective strategies for early prevention or delayed onset of AD, among them identifying risk-reducing modifiable environmental/lifestyle factors such as diet, are needed.
Although a great interest on the association between diet and AD has emerged, much of the efforts have been spent over the years on studying individual nutrients or food items. However, current literature is inconsistent. This could be partly due to the fact that humans eat meals with complex combinations of nutrients or food items that are likely to be synergistic (or antagonistic) so that the action of the food matrix is different from the individual nutrients or food items. In addition, nutrients or food items are highly correlated within foods, so it is difficult to examine their individual effects. Furthermore, the effect of a single nutrient may be too small to detect, or, a statistically significant association might be simply found by chance alone, due to an increased type 1 error in the case of multiple comparisons of a large number of nutrients.
Limited evidence suggests that a dietary pattern containing an array of vegetables, fruits, nuts, legumes and seafood consumed during adulthood are associated with lower risk of age-related cognitive impairment, dementia and Alzheimer’s disease. Although the number of studies available on dietary patterns and neurodegenerative disease risk is expanding, this body of evidence, which is made up of high-quality observational studies, has appeared only in recent years and is rapidly developing. It employs a wide range of methodology in study design, definition and measurement ascertainment of cognitive outcomes and dietary pattern assessment.
Nutrition is an important modifiable risk factor that plays a role in the strategy to prevent or delay the onset of dementia. Research on nutritional effects has until now mainly focused on the role of individual nutrients and bioactive components. However, the evidence for combined effects, such as multi-nutrient approaches, or a healthy dietary pattern, such as the Mediterranean diet, is growing. These approaches incorporate the complexity of the diet and possible interaction and synergy between nutrients. Over the past few years, dietary patterns have increasingly been investigated to better understand the link between diet, cognitive decline and dementia.
The role of the Mediterranean diet on cognitive decline and dementia risk was only recently systematically reviewed by Lourida et al. (8). This review included literature published until January 2012. In addition, Alzheimer’s Disease International published a report on the available evidence on this subject in the beginning of 2014.
Still there is more unknown in the field.
Additional research is needed.
- Cognitive impairment represents an array of disease processes with unique etiologic risk factors incorporating genetic and environmental variables. Thus, future studies of dietary relationships should increasingly focus upon clearly defined disease subtypes and employ precise diagnostic criteria and quantitative outcomes relevant to the specific disease process.
- Improvements in the objective measurement of cognitive outcomes, standardization of tools and measurement over multiple time points in prospective population studies are needed. Several studies included in this review did not measure decline per se, but cognitive function at a single time point. Future studies should measure cognitive function prospectively to assess changes over time using methods appropriate for cognitively impaired participants.
- Improve methods for assessing dietary patterns more comprehensively, precisely and with standardization so that investigators can better define habitual food intake behaviors in populations and allow more informative comparisons of results among studies. These efforts in the area of cognitive impairment may require unique tools as impaired individuals may not provide accurate data on past or current intake.
- Examine dietary patterns and associations with cognitive impairment, dementia and Alzheimer’s disease in studies with strong methodological design (i.e., longer duration of follow up, assessment of dietary intake at various time points over the course of the study, adjustment for potential confounders and assessment of exposures and outcomes using validated methods). Examine a range of clearly defined patterns consumed in the United States (e.g., the Dietary Guidelines for Americans, vegan, Mediterranean).
- Determine the relationships between dietary patterns at early time points the life cycle and risk of cognitive impairment, dementia and Alzheimer’s disease later in life.
- Determine if dietary patterns impact cognitive impairment, dementia and Alzheimer’s disease in diverse populations with varying cultural, ethnic and socioeconomic backgrounds.
- Use the results from observational studies to design targeted interventions that test the impact of dietary pattern change on cognitive impairment, dementia and Alzheimer’s disease in combination with relevant pharmacologic and behavioral interventions.
Micha Shalev MHA CDP CDCM CADDCT is the owner of The Oasis at Dodge Park, Dodge Park Rest Home and The Adult Day Club at Dodge Park located at 101 and 102 Randolph Road in Worcester. He is a graduate of the National Council of Certified Dementia Practitioners program, and well-known speaker covering Alzheimer’s and dementia training topics. He can be reached at 508-853-8180 or by e-mail at [email protected] or view more information online at www.dodgepark.com.