Part D. Chapter 2: Dietary Patterns, Foods and Nutrients, and Health Outcomes - Continued
Dietary Patterns and Neurological and Psychological Illnesses
Existing Evidence around Foods and Nutrients and Neurological and Psychological Illnesses
Neuropsychological development and function is increasingly recognized as a high national priority for health promotion and chronic disease prevention. Two major components of neuropsychological function are cognition, the ability to reason, and mood, balanced and appropriate to enable optimal cognition.
Nutrition for optimal neurodevelopment in very young children has long been a subject of research. The 2010 DGAC concluded that moderate evidence supported a positive relationship between maternal dietary intakes of n-3 from seafood and improved cognitive ability in infants.151 The rising numbers of U.S. older adults and the potential human and financial cost of age-related cognitive impairments, such as Alzheimers disease and other dementias, also have helped drive national interest in chronic mental disease.152 153 Separately, depression affected 8 percent of Americans for at least two weeks annually from 2007-2010, and of these, 80 percent report functional impairment.154 Many preclinical and human studies have established relationships between traditional nutrients (e.g., omega-3 fatty acids) and central nervous system composition and function. Studies appearing in the last few years reflect the increasing research interest in the links between diet and neurological health.
The hypothesis that nutrition can reduce and/or play a role in the treatment of these mental diseases and their related burdens has been studied in relation to several nutrients and foods, including the B vitamins, vitamin E, and selenium.155 156 The omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are among the most studied nutrients for neural health, in part because DHA is a major component of the brain, specifically gray matter and its synapses, and the specialized light detecting cells of the retina. DHA, in particular, supports the amplitude and signaling speed of neural response. EPA has emerged as a nutrient with antidepressive properties and continued studies to define its role in prevention and therapy are underway. Sufficiently strong medical evidence has been obtained for EPA and DHA such that supplements are now considered as complementary therapy for major depressive disorder by the American Psychiatric Association157 and more recent data from a meta-analysis has found them effective.158 Before 2010, the number of published dietary pattern studies was small. However, a more substantial literature on dietary patterns and neuropsychological health has been published since 2010. The DGAC was therefore able to consider prevention of adult neuropsychological ill health for the first time.
Question 6: What is the relationship between dietary patterns and risk of neurological and psychological illnesses?
Source of evidence: NEL systematic review
Limited evidence suggests that a dietary pattern containing an array of vegetables, fruits, nuts, legumes and seafood consumed during adulthood is associated with lower risk of age-related cognitive impairment, dementia, and/or Alzheimers 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. DGAC Grade: Limited
Limited evidence suggests that dietary patterns emphasizing seafood, vegetables, fruits, nuts, and legumes are associated with lower risk of depression in men and non-perinatal women. However, the body of evidence is primarily composed of observational studies and employs a range of methodology in study design, definition, and measurement of dietary patterns and ascertainment of depression/depressive signs and symptoms. Studies on dietary patterns in other populations, such as women in the post-partum period, children and adolescents, as well as those in various ethnic and cultural groups, are too limited to draw conclusions. DGAC Grade: Adults Limited; Children, adolescents, and women in the post-partum period Grade not assignable
Dietary patterns emphasizing vegetables, fruits, seafood, legumes and nuts similar to those that achieve chronic disease risk reduction are consistent with maintaining neurocognitive health, including cognitive ability in healthy aging, and balanced mood.
Review of the Evidence
Dietary Patterns and Cognitive Impairment, Dementia, and Alzheimers Disease
This systematic review includes 30 articles (two articles analyzed data taken from RCTs and 28 articles used data from prospective cohort studies) published since 1980 (with all but two published since 2008) that examined the relationship between dietary patterns and age-related cognitive impairment, dementia, and/or Alzheimers disease.159-188 Twenty of the articles included in this review assessed the relationship between dietary patterns and cognitive impairment, 10 articles examined cognitive impairment or dementia, and eight articles looked at Alzheimers disease.
The articles used several different methods to assess dietary patterns. Two articles analyzed data from RCTs that tested or described dietary patterns, 23 articles used indices/scores to assess dietary patterns quality or adherence, three articles used data-driven methods, and three used reduced rank regression. Most (18 of 28) articles found an association between dietary patterns and age-related cognitive impairment, dementia, and/or Alzheimers disease. Despite some heterogeneity in this body of evidence, some common elements of dietary patterns were associated with measures of cognitive impairment, dementia, and/or Alzheimers disease:
- Patterns higher in vegetables, fruits, nuts, legumes, and seafood were generally associated with reduced risk of age-related cognitive impairment, dementia, and/or Alzheimers disease.
- Patterns higher in red and/or processed meats were generally associated with greater age-related cognitive impairment. Relatively few studies reported on refined sugar and added salt, and patterns including these nutrients tended to report greater cognitive impairment.
Although some studies included participants from a range of race/ethnic and socioeconomic groups, the results are most applicable to the general healthy aging population. In addition, dietary patterns were derived using dietary intake measured at baseline only, and therefore, may not reflect patterns consumed throughout relevant periods of life before enrollment in the study, or changes in intake that may have occurred over the duration of the study. Similarly, several studies measured cognitive function only at a single time point (follow-up), and therefore, could not assess change in cognitive function over time. Finally, though these studies controlled for a number of confounders, not all apparently relevant potential confounders were adjusted for (e.g., existing or family history of cognitive decline, dementia, or Alzheimers disease; baseline health status; changes in dietary intake over time) and, as with all association studies, residual confounding is possible.
Dietary Patterns and Depression
This systematic review includes nineteen articles (17 from prospective cohort studies, and 2 using data from RCTs) published since 1980 (all of which were published since 2008) that assessed the relationship between dietary patterns and depression.175 182 189-205
The articles used several different methods to assess dietary patterns. Two studies tested the effects of dietary patterns as part of an RCT, six articles used indices/scores to assess dietary patterns, 10 articles used data-driven methods, and one used reduced rank regression. Despite methodological and outcome heterogeneity in this body of evidence, some protective dietary patterns emerged:
- Patterns emphasizing seafood, vegetables, fruits, and nuts, were generally associated with reduced risk of depression.
- Patterns emphasizing red and processed meats and refined sugar were generally associated with increased risk of depression.
This body of evidence did have several limitations. There was considerable variability in how the outcome of depression was assessed, with some studies using various depression scales, some using physician diagnosis/hospital discharge records, and others using proxies such as use of depression medication. Although most studies make extensive efforts to include participants across a wide range of race/ethnic groups and across the socio-economic continuum, there still may be some subgroups for which the association between dietary patterns and depression risk cannot be reliably assessed and therefore conclusions cannot be drawn for them. Research is needed to determine whether dietary patterns are associated with risk of depression in particularly vulnerable subgroups, specifically children, adolescents, young adults, and women during the post-partum period. Additional limitations within this body of evidence make it difficult to draw stronger conclusions, including assessment of dietary patterns and depression outcomes at a single point in time, potential for residual confounding despite adjustment for a number of factors, and few studies conducted in U.S.-based populations.
For additional details on this body of evidence, visit: http://NEL.gov/topic.cfm?cat=3352