Below is a summary of published research that has been supported in part by California Walnut Commission on life expectancy, healthy aging, and cognitive function.
Walnuts and Longevity
According to a study2 by researchers from the Harvard T.H. Chan School of Public Health, higher walnut consumption – both in terms of the amount and frequency – may be associated with a lower risk of death and an increase in life expectancy among older adults in the U.S., compared to those who do not consume walnuts. This study found five or more servings of walnuts per week (one serving = one ounce) may provide the greatest benefit for mortality risk and life expectancy. Eating five or more servings per week was associated with a 14% lower risk of death (from any cause), 25% lower risk of dying from cardiovascular diseases, and a gain in about 1.3 years of life expectancy, compared to those who didn’t consume walnuts. As a prospective observational study, these results do not prove cause and effect, but they do shed light on how walnuts may support an overall healthy lifestyle that promotes longevity.
Walnuts and Physical Function
Findings published in The Journal of Nutrition suggest that consumption of 1-2 servings of walnuts per week (1/4 cup per serving) was associated with reduced risk of developing impairments in physical function in older women, which may help to maintain independence throughout the aging process.3 Researchers looked at data from 54,762 women in the Nurses’ Health Study, which tracked women for over 30 years. This paper emphasized that overall diet quality, rather than individual foods, may have a greater impact on reducing risk of physical function impairments. Specifically, diet quality traits most associated with reduced rates of incident physical impairment were higher intake of fruits and vegetables; lower intake of sugar-sweetened beverages, trans fat, and sodium; and moderate alcohol intake. Among food components, the strongest relations were found for increased intakes of oranges, orange juice, apples, pears, romaine or leaf lettuce, and walnuts. Study limitations should be considered. The sample only included women, so these results may not be generalizable to men. Additionally, participants were not assigned to eat walnuts or other foods, and were just asked about their dietary choices. It is also possible that subjects may have misreported their dietary intake since this information was collected by questionnaires. In addition, because this is an observational study, residual confounding cannot be ruled out (i.e., that other lifestyle habits which are more common in adults who eat walnuts could contribute to the study findings) and, thus, the results should be interpreted with caution.
Walnuts and the Fight Against Alzheimer’s Disease
An animal study published in the Journal of Alzheimer’s Disease found that a diet including walnuts may play a role in reducing the risk of Alzheimer’s disease.4 Researchers examined the effects of dietary supplementation with 6% or 9% walnuts in mice (equivalent to 1 ounce and 1.5 ounces of walnuts per day in humans) compared to a control diet with no walnuts. The study found significant improvement in learning ability, memory, reducing anxiety, and motor development in mice fed a walnut-enriched diet. Since this study was performed on animals, findings cannot yet be correlated to humans. Animal studies are provided as background and used to formulate hypotheses for additional research needed to determine the effects on humans.
Walnuts and Memory
A publication in The Journal of Nutrition, Health & Aging revealed that eating walnuts was associated with improved performance on cognitive function tests, including those for memory, concentration, and information processing speed.5 Participants included adults ages 20-59 as well as 60 and over. Cognitive function was consistently greater in adult participants that consumed walnuts, regardless of age, gender, or ethnicity. Given this was an observational study, the findings cannot prove causality and there may have been underlying differences between the study groups. The findings are based on single 24-hour recalls, which reflect only one day of food intake. Additionally, the presence of an effect in studies of older individuals, but not among young college students, might reflect a greater vulnerability in older subjects and therefore a greater potential benefit.
Mediterranean Diet and Cognition
Eating a Mediterranean diet supplemented with olive oil or nuts (primarily walnuts) may reduce the risk of age-related cognitive decline in an older population, according to a study published in the Journal of the American Medical Association Internal Medicine.6 Participants, a subcohort of the Prevención con Dieta Mediterránea (PREDIMED) trial, were randomly assigned to a Mediterranean diet supplemented with mixed nuts (15g walnuts, 7.5g almonds, and 7.5g hazelnuts per day) or extra virgin olive oil (at least 50g or 4 tablespoons per day), or a low-fat diet (control group). The study found that participants who consumed a Mediterranean diet with nuts, including walnuts, showed improvements in memory compared to a control diet. Study limitations to consider are that this is an analysis of a subsample in a larger clinical trial that was not specifically designed to examine cognition and the overall sample size was small. Due to the differential results for the Mediterranean diet on cognitive composites, it is difficult to precisely delineate what part of the diet was associated with preventing cognitive decline. Researchers experienced losses to follow-up, predominantly in the control group, probably because participants did not receive food incentives. Given the long recruitment period, intervals of follow-up cognitive assessments were unavoidably unequal. Additionally, the cohort was selected for high vascular risk, which prevents generalizing the results to the average elderly population.
Nuts and Healthy Aging
A study found that women who consumed at least two servings of walnuts per week during their late 50s and early 60s were more likely to age healthfully compared to those who did not eat nuts. In this study, “healthy aging” was defined as having no chronic diseases, reported memory impairment, or physical disabilities as well as having intact mental health after the age of 65. Researchers looked at data from 33,931 women in the Nurses’ Health Study to evaluate the association between nut consumption and overall health and well-being in aging. After accounting for various factors that could impact health in older adults such as age, education, income, BMI, calorie intake, smoking, physical activity, and diet quality, researchers found a significant association between total nut intake (including peanuts, walnuts, and other nuts) and higher odds of healthy aging.
