Maintaining cognitive health is an essential aspect of healthy ageing. As people live longer and the population ages, age-related cognitive decline and neurodegenerative disorders, such as dementia, are becoming a growing concern for public health. Dementia, especially Alzheimer’s disease, is currently one of the top ten causes of mortality among all diseases and a significant cause of disability and dependency among older adults worldwide. The physical, psychological, social, and economic impacts of cognitive decline and dementia not only affect the individuals themselves but also their caregivers, families, and society at large. Therefore, addressing this issue is crucial for promoting public health.
A recent analysis of epidemiological literature on the relationship between nut consumption and cognitive activity identified a total of 15 papers, including seven cross-sectional and eight prospective cohort studies. Thirteen of these studies demonstrated a positive correlation between nut intake and cognitive function, although not all cognitive tests showed favourable relationships in every study. The findings were published in the journal Nutrients.
The researchers also noted that some cross-sectional studies have shown that nut consumption is associated with better cognitive functioning. For instance, a cross-sectional investigation was conducted as part of the Prevención con Dieta Mediterránea (PREDIMED) project, which examined the relationship between different diets and cognitive function. This study found that coffee, olive oil, wine, and walnuts, but not total nuts, were associated with improved cognitive function, regardless of known risk factors for cognitive decline and other dietary consumption. Interestingly, the study also found that total urinary polyphenol excretion, an objective indicator of consumption of polyphenol-rich foods, had a direct correlation with working memory function.
When it comes to specific types of nuts, walnuts were the most extensively examined and were reported to be connected with improved cognitive performance compared to low or non-consumers. But most studies analyzed the total nut intake as a whole and either did not or could not differentiate the analyses according to the different varieties of nuts.
In two PREDIMED sub-studies that were both long-term and well-powered, the impact of nut-supplemented Mediterranean diets on cognitive performance was assessed. These studies showed that older individuals at high risk of cardiovascular disease benefited from the intervention, although it should be noted that improved cognitive functioning may not have been solely due to nut consumption, as other components of the Mediterranean diet were also modified.
Still, the Mediterranean diet supplemented with nuts was shown to decrease the relative risk of stroke by around 50% in the PREDIMED study, providing further evidence for the neuroprotective effects of nuts.
But it’s important to acknowledge the limitations of the current evidence and to consider these when planning future research. There is a shortage of studies investigating the relationship between nuts and cognition, particularly in individuals under the age of 60, and no research has yet examined whether diets containing nuts have any impact on hard clinical outcomes such as dementia or Alzheimer’s disease.
Based on the strength of the evidence regarding the relationship between nut and walnut consumption and heart disease, the US Food and Drug Administration released qualified health claims for these foods in 2003 and 2004, respectively. The claims stated that “supportive but not conclusive research shows that eating 1.5 ounces per day of nuts/walnuts, as part of a low saturated fat and low cholesterol diet and not resulting in increased caloric intake, may reduce the risk of coronary heart disease.” This beneficial effect has been confirmed by research over the last two decades, and a similar qualified health claim has more recently been issued for macadamia nuts.
Considering the shared risk factors between common heart and brain diseases, as well as the numerous beneficial effects and safety of nut consumption, this recommendation for reducing the risk of coronary heart disease through nut consumption may also be applied to the prevention of cognitive decline and dementia, pending additional evidence.
The study’s findings indicate that although the clinical, epidemiological, and mechanistic evidence for the impact of nuts on cognitive functioning is not strong or definitive, the results suggest that nuts could contribute to maintaining cognitive function and potentially reducing cognitive decline in individuals of all ages, particularly older adults. Given the potential cognitive health benefits of nuts, including them in a healthy diet could be a viable public health strategy for preventing cognitive decline in the majority of people.
