Can What You Eat Influence Cognition, Particularly in Older Individuals?

Declining cognitive ability is a common issue as humans age. Dementia, a term that collectively refers to an impairment in the ability to remember, think, or make decisions that interferes with everyday activities. Even though dementia is most commonly observed in older adults, it is not a normal aspect of the aging process. Alzheimer disease is the most common type of dementia representing between 60% and 80% of all cases of dementia.

Mild cognitive impairment is considered to represent a transition state between normal aging and the development of Alzheimer disease. Genetically at-risk individuals have been shown to have pathophysiological changes even decades before the onset of dementia.

The composition of one's diet has been suggested to contribute to the prevention from cognitive decline. Food composition such as B vitamins, ascorbic acid (vitamin C), tocopherols (vitamin E), omega-3 fatty acids, plant polyphenols and flavonoids, as well as caffeine and the composition of gut microbiota have been implicated in cognitive improvement and to reduce the risk for dementia.

For example, it has been shown that consumption of the typical Mediterranean diet is associated with improved cognitive function as well as decreased cognitive decline.

Mediterranean Diet, Cognitive Function, and Dementia: A Systematic Review

Mediterranean Diet and Risk of Dementia

A recent review published in the journal, Nutrition, looks at the effects of diet composition on cognition in older individuals, particularly as it relates to Alzheimer disease.

Eat for better cognition in older adults at risk for Alzheimer’s disease

This review looked at numerous reports of the effects of diet on cognition. One study found that consumption of a modified Mediterranean-ketogenic diet was associated with increased cerebral perfusion and cerebral ketone body uptake decreased cerebrospinal fluid levels of the protein tau. The tau protein is predominantly localized to neurons and it becomes misfolded in the brains of individuals with Alzheimer disease. The Mediterranean-ketogenic diet has also been shown to modify the gut microbiome to a more favorable composition.

A comparison of individuals consuming a low carbohydrate diet (5%-10% of total calories) versus a high carbohydrate diet (50% of total calories) found that after 6 weeks an assessment of verbal memory showed improvement in the low carbohydrate consuming participants.

Cognition has also been shown to be improved when individuals consume a low saturated fat and low glycemic index diet for 4 weeks. This study also looked at cerebrospinal fluid (CSF) amino acid levels since changes in these constituents are linked to changes in Alzheimer disease associated CSF biomarkers.

Older individuals with mild cognitive impairment, who adhered to an intermittent fasting diet, have been shown to exhibit cognitive improvement following 3 years on the diet. These improvements were not found in similar individuals who only irregularly practiced an intermittent fasting diet.

Different dietary constituents have also been shown to exert positive effects on cognition. Diets that include sesame oil cake extract or a Mediterranean diet along with long-term high phenolic early harvest extra virgin olive oil both were associated with improvement in cognition compared to matched placebo controls. Other dietary components such as grape juice, tempeh, Brazil nuts, cosmos caudatus (also known as King's salad) have all been found to be associated with improved cognitive function.

Individual dietary constituents have also been studied for their potential benefits in relation to cognitive improvement and/or decreases in cognitive decline. Phosphatidylserine plus phosphatidic acid consumption in older adults with memory impairment for a period of 3 months was associated with dramatically enhanced memory compared to placebo controls.

In individuals with mild cognitive impairment there is an association between low vitamin B₁₂ concentrations and memory performance. Thus, adequate dietary folate and B vitamins (particularly B₁₂) may contribute to cognitive function and this is predicted to be the result these vitamins on the methylation status of specific redox-related genes. The role of folate and B₁₂ in the synthesis of S-adenosylmethionine (SAM), the methyl donor for DNA and histone methylation, is discussed in detail in my website.

Individuals who take a daily oral folic acid supplement, along with the omega-3 polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA), for 6 months showed significantly improved cognitive function. However, individuduals who took 500 mg of methylcobalamin (a form of vitamin B₁₂) and 400 mg of folic acid once daily for 2 years did not show improvements in cognitive deterioration compared to placebo controls. In addition, supplementation with B vitamins has been reported to slow cognitive decline only in individuals with higher baseline levels of omega-3 PUFA.

With respect to dietary supplementation with specific types of lipids it has been shown a ketogenic diet containing medium-chain triglycerides (MTG) composed of 60% caprylic acid and 40% capric acid resulted in improved episodic memory, processing speed, and language ability.

Supplementation with antioxidant vitamins such as vitamin A, C, and E is predicted to result in decreases in the rate of cognitive decline. However, despite significant improvements in most oxidative stress indicators, supplementation with vitamin C and E for 1 year did not improve cognitive performance compared with placebo controls.

Astazanthin is a potent antioxidant found in numerous plants and in seafood such as krill. In individuals taking astazanthin for 12 weeks there were increased measures of cognitive ability compared to placebo controls.

TAKE AWAY: A proper diet (preferably NOT the typical Western style diet) composed of specific foods and supplements can positively affect cognitive functioning as well as reduce the potential for cognitive decline.