DIETARY FIBER INTAKE AND REDUCED MORTALITY RISK
Park Y, Subar AF, Hollenbeck A, and Schatzkin A. Dietary fiber intake and mortality in the NIH-AARP Diet and Health Study. Arch Intern Med. 2011; doi:10.1001/archinternmed.2011.18
Dietary fiber, in some studies, is linked with reduced overall mortality and reduced risk for cardiovascular-related death. In addition to its effects on cardiovascular disease, it is proposed that dietary fiber may be protective against diabetes, obesity, and some cancers. However, aside from studies on cardiovascular disease, there are relatively few studies on the effects of dietary fiber on cause-specific mortality. The protective effects of dietary fiber may be related to its effects on gastrointestinal transit, excretion of toxins, cholesterol levels, or glucose handling. To better understand the role of dietary fiber intake and mortality, Park et al. examined the effect of dietary fiber on total and cause-specific death.
Data from participants enrolled in the NIH-AARP (National Institutes of Health-American Association of Retired Persons) Diet and Health Study were used. The NIH-AARP Diet and Health Study included 567,169 individuals who were between the ages of 50 and 71 years in 1995–1996. Participants completed baseline food frequency questionnaires as well as demographic, health, and lifestyle surveys. Dietary intake data were analyzed for total fiber content and food-specific fiber content. Fiber intakes were stratified into quintiles (Q1 = 12.6 g/d; Q2 = 16.4 g/d; Q3 = 19.4 g/d; Q4 = 22.9 g/d; Q5 = 29.4 g/d). The primary outcome measure was mortality and was determined through links to the Social Security Administration Death Master File and the National Death Index Plus. Deaths were classified as due to cardiovascular disease, infectious disease, respiratory disease, accidents, and all other causes.
Over an average of 9 years of follow-up, 20,126 deaths in men and 11,330 deaths in women were observed. Dietary fiber intake was associated with lowered risk for overall mortality as well as mortality from cardiovascular, infectious, and respiratory disease in both men and women. Higher dietary fiber intake from grains, but not other food sources, was significantly related to a reduced risk for mortality. The authors acknowledge that higher fiber intake may be indicative of an overall healthier diet relative to a diet lower in fiber, and that the link between high fiber intake and reduced mortality risk should not be interpreted as causative. Based on data from this large, well-conducted, prospective cohort study, the authors suggest that intake of dietary fiber, particularly whole-grain fiber, may reduce risk of premature death from cardiovascular disease, infectious disease, or respiratory illness.
Comment: Drs. de Koning and Hu in an accompanying editorial emphasize the importance making a distinction between the effects of dietary fiber and the effects of whole grains. They argue that fiber isolates or supplements would likely not confer the same benefits as whole grains and recommend that individuals focus on substituting whole grains for refined grains to maximize health benefits.
Comment: de Koning L and Hu FB. Do the health benefits of dietary fiber extend beyond cardiovascular disease? Arch Intern Med. 2011; doi:10.1001/archinternmed.2011.19
LONG-TERM EFFECTS OF ZINC AND IRON SUPPLEMENTATION ON COGNITIVE FUNCTION IN CHILDREN
Pongcharoen T, Digirolamo AM, Ramakrishnan U, Winichagoon P, Flores R, and Martorell R. Long-term effects of iron and zinc supplementation during infancy on cognitive function at 9 y of age in northeast Thai children: a follow-up study. Am J Clin Nutr. 2011; 93:636–643.
Children born in developing nations are at risk for nutrient deficiencies due, in part, to low availability of food or poor nutrient content of available food. Iron and zinc deficiencies may be of particular concern as these nutrients are essential for brain development and function. Furthermore, iron-deficiency-related anemia can negatively affect cognitive development. Supplementation with iron and zinc during infancy improves iron and zinc status, but findings related to cognitive performance have been inconsistent. Some short-term studies in infants given zinc and iron supplements suggest modest benefits in psychomotor development, while other studies show no improvement. Pongcharoen et al. examined the long-term effects of zinc and iron supplementation in infancy on cognitive performance in older children.
Children in this study were originally enrolled in a randomized controlled trial of iron and zinc supplementation in infants in northeast Thailand. Infants (n = 675) between the ages of 4 and 6 months were randomly assigned to one of four conditions: 10 mg/d iron (ferrous sulfate); 10 mg/d zinc (zinc sulfate); 10 mg/d each of iron and zinc; or placebo. Supplements were given daily for a period of 6 months. At baseline, the prevalence of anemia was 28%, the prevalence of iron deficiency was low (between 3.4 and 6.2%, depending on cut-off criteria), and the prevalence of low zinc status ranged from 4.5 to 6.2%. No cognitive assessments were conducted in the original study. Children (n = 560) aged 9 years were enrolled in the presently reported follow-up cross-sectional study. Cognitive performance was assessed using standard scales, including the Thai version of the Wechsler Intelligence Scale for Children–Third Edition, Raven's Colored Progressive Matrices, as well as measures of academic performance.
No differences in IQ, cognitive test performance, or academic performance were seen as a function of zinc or iron supplementation. Iron and zinc supplementation during infancy improved nutrient status and hemoglobin concentrations in these children, but supplementation was not continued through childhood. The authors suggest that brief (6-month) interventions in infancy may be insufficient to overcome prenatal and postnatal nutrient insufficiency.
FLAVONOID INTAKE AND COGNITIVE FUNCTION IN THE LOTHIAN BIRTH COHORT 1936
Butchart C, Kyle J, McNeill G, Corley J, Gow AJ, Starr JM, and Deary IJ. Flavonoid intake in relation to cognitive function in later life in the Lothian Birth Cohort 1936. Br J Nutr. 2011; doi: 10.1017/S0007114510005738
Research linking intake of flavonoid-rich foods such as red wine, tea, vegetables, fruit, and cocoa with improved cognitive function suggests that risk for age-related cognitive decline is nutritionally modifiable. Flavonoids are thought to exert protective effects on brain function via antioxidant and anti-inflammatory mechanisms, as well as via cardioprotective mechanisms. Although a number of studies suggest that diets high in flavonoids are associated with a reduced risk for dementia, these studies cannot control for the degree to which these findings are influenced by early-life differences in intelligence, education, and socioeconomic status. Using longitudinal cognitive data from the Lothian Birth Cohort, Butchart et al. investigated the role of flavonoids in cognitive aging while controlling for childhood cognitive ability.
The Lothian Birth Cohort 1936 is comprised of independently-living men and women who were born in 1936 in or near the city of Edinburgh (n = 1091). Cognitive function was assessed at the age of 11 years and again at 70 years. The cognitive tests performed at both 11 and 70 years of age assessed general intelligence and verbal reasoning with the Moray House Test. Cognitive testing at age 70 included the Mini-Mental State Exam, verbal fluency, executive function, and non-verbal memory. At age 70, participants also completed food frequency questionnaires that were validated for the Scottish population. Intake of flavonoid subclasses was estimated using a flavonoids database. Intake of flavonoid-rich foods and drinks was also analyzed.
Prior to adjusting for childhood intelligence, intakes of fruit and red wine were positively associated with higher scores on some cognitive tasks, and tea intake was associated with lower scores on some tests. However, when adjusted for childhood intelligence scores, the associations were no longer statistically significant.
The authors conclude that the present data do not support a role for flavonoid intake in the prevention of cognitive decline. They propose that childhood intelligence influences not only education and occupation, but also food choices and healthy lifestyle choices, all of which contribute to mental status in older age. A limitation to this interpretation in the Lothian Birth Cohort 1936 is that food intake was only measured at age 70, so lifetime food intake patterns are not likely reflected. This study underscores the importance of including, when available, estimates of cognitive ability in childhood when performing studies evaluating the nutrient status and cognitive performance in adults and older individuals.