Plant-based diets characterized by frequent consumption of fruits and vegetables, legumes, whole-grain products, high-quality protein and fat sourced from fish and seafood, as well as limited intake of refined carbohydrates, sodium, and saturated fatty acids, are highly encouraged as part of a healthy dietary pattern. Most well-known dietary patterns include the Mediterranean diet, the dietary approaches to stop hypertension (DASH), and traditional Japanese and Nordic diets, which have shown beneficial effects on diabetes, insulin sensitivity, blood pressure, lipid profile, and cognition. Subclinical deficiencies in essential micronutrients, such as vitamin C, vitamin E, and β-carotene, as well as vitamin B12, B6, and folate, have been associated with progressive cognitive decline. These plant-based dietary factors are considered a first-line strategy to prevent or potentially delay cognitive decline (1).

 

    Previous blogs have touched on a few plant-based factors on cognitive function such as Purple Foods Rich in Anthocyanins Can Improve Cognitive Function and Neuroprotective Effects of Ellagic Acid. This blog will talk about the role of carotenoids, which are naturally occurring pigments found in red, yellow, orange, and dark green fruits and vegetables, and powerful antioxidants in the prevention of cognitive function decline.

 

    A prospective study is a type of study where participants are enrolled in the study before they develop the disease or outcome in question. This type of study can lead to a good understanding of the contributing factors to the onset of a specific disease condition.

 

    The relationship between long-term intakes of carotenoids to subjective cognitive function (a self-reported, validated indicator of cognitive dysfunction) was examined in a prospective study. Among 49,493 female registered nurses with a mean age of 48 years of age in 1984, multinomial logistic regression to estimate the Odd ratios (ORs) relating intakes of carotenoids to self-reported subjective cognitive function in 2012 and 2014 (a 28 year follow up study). Mean intakes of carotenoids were calculated from 7 repeated Food frequency questionnaires collected in 1984, 1986, and every 4 y afterward until 2006. Self-reported subjective cognitive function was assessed by a 7-item questionnaire on changes in memory and cognition; validity was supported by strong associations with Apolipoprotein E (APOE) ε4 genotype and concurrent cognitive function and cognitive decline measured by telephone-based neuropsychological tests. The mean values of scores assessed in 2012 and 2014 were categorized as "good" (0 points, 40.8%), "moderate" (0.5–2.5 points, 46.9%), and "poor" (3–7 points, 12.3%) (2).

 

    This study showed that the higher intake of total carotenoids was associated with substantially lower odds of moderate or poor cognitive function after controlling for other dietary and non-dietary risk factors and total energy intake. Comparing the top with the bottom quintile of total carotenoids (a marker for total fruits and vegetable intake), the multivariable ORs were 0.86 (95% CI: 0.80, 0.93; p < 0.001 meaning a 14% risk reduction) for moderate subjective cognitive function and 0.67 (95% CI: 0.60, 0.75; p < 0.001 meaning a 33% risk reduction) for poor subjective cognitive function. Similar associations were found for total β-carotene, dietary β-carotene, αcarotene, lycopene, lutein + zeaxanthin, and β-cryptoxanthin. The significant associations for β-cryptoxanthin, lycopene, and lutein + zeaxanthin persisted after mutual adjustment for each other (2).

 

    Oxidative stress is involved in age-related cognitive decline. The dietary antioxidants, including carotenoids, tocopherols, and vitamin A may play a role in the prevention or delay in cognitive decline.

 

    A group of scientists analyzed antioxidant contents from samples obtained from 78 octogenarians and 220 centenarians from the Georgia Centenarian Study (3). Brain tissues were obtained from 47 centenarian decedents. Analyzed antioxidant concentrations were compared with cognitive tests designed to evaluate global cognition, dementia, depression, and cognitive domains (memory, processing speed, attention, and executive functioning). Blood carotenoid levels including lutein, zeaxanthin, and β-carotene concentrations were most consistently related to better cognition (p < 0.05) in the whole population and the centenarians. Only blood lutein was significantly related to better cognition in the octogenarians. In the brain, lutein and β-carotene were related to cognition with lutein being consistently associated with a range of measures. There were fewer significant relationships for α-tocopherol and a negative relationship between brain retinol concentrations and delayed recognition. These findings suggest that the status of certain carotenoids in the old may reflect their cognitive function (3).

 

    To test whether healthy dietary supplementation may improve cognitive function, cognitively healthy individuals aged 65+ years (n=30 each group) consumed daily 1 g fish oil (of which 430 mg docosahexaenoic acid, 90 mg eicosapentaenoic acid), 22 mg carotenoids (10 mg lutein, 10 mg meso-zeaxanthin, 2 mg zeaxanthin), and 15 mg vitamin E or placebo for 24 months in a double-blind, placebo-controlled, randomized clinical trial (4).

 

    Following 24-month supplementation, individuals in the active intervention exhibited improvements in working memory. Spatial working memory total errors: the number of times a box is selected that is certain not to contain a token and therefore should not have been visited by the individual. A significantly less number of errors was observed between active and placebo groups for both spatial working memory task (SWM) total errors at stage 8 (stage 8 involves 8 boxes) and SWM total errors across all stages (all stages is the sum of stages 4, 6, and 8). The magnitude of change of carotenoid concentrations in tissue, and ω-3FA and carotenoid concentrations in blood were related to the magnitude of change in working memory performance (4).

 

    Working memory is a key component of executive function that is responsible for the temporary holding of information for later access and application (e.g. holding a person's telephone number or address in mind, listening and responding to information spoken during a conversation). Brain regions involved in working memory include the prefrontal cortex, parietal regions, and hippocampus. More specifically, working memory involves the encoding of stimuli (e.g. words, pictures) and can involve attending to just one feature of a stimulus (i.e. selective attention) (e.g. tuning out the various sounds in a busy restaurant to listen to your friend tell a story), or attending to multiple features of a stimulus (i.e. divided attention or multi-tasking) (e.g. singing along to a song on the radio while driving). In terms of clinical significance, the observed improvements in working memory can translate into practical benefits for day-to-day function. Improved working memory can enhance the capacity to retain information and prioritize the steps needed to make decisions and solve problems. Enhancing working memory can also aid individuals in focusing on the task at hand such as planning and prioritizing tasks for the day ahead or remembering key information (e.g. keeping appointments) (4).

 

    As a representative marker of a plant-based diet, carotenoids had been shown to exist in higher levels in the blood and brain tissues which were associated with better cognitive functions in humans (2, 3), and supplementation of carotenoids could lead to improved working memory (4).

 

    Carotenoids are phytochemicals that only plants can produce, we humans cannot synthesize thus have to obtain them via dietary intake. A plant-based diet has many health benefits. A previous blog of Gou Qi Zi – A Gift from Nature talked about the benefits of carotenoids lutein and zeaxanthin on vision. Both eyes and the brain belong to the central nervous system. A plant-based diet (carotenoids rich diet) is beneficial for keeping both visual and mental sharpness.

 

References:

1. Kouvari, M., et al. (2022) Metabolic Syndrome, Cognitive Impairment and the Role of Diet: A Narrative Review. Nutrients. 2022 Jan; 14(2): 333. doi: 10.3390/nu14020333

2. Yuan, C., et al. (2020). Long-Term Intake of Dietary Carotenoids Is Positively Associated with Late-Life Subjective Cognitive Function in a Prospective Study in US Women. The Journal of Nutrition. doi:10.1093/jn/nxaa087

3. Johnson, E. J., et al. (2013). Relationship between Serum and Brain Carotenoids,α-Tocopherol, and Retinol Concentrations and Cognitive Performance in the Oldest Old from the Georgia Centenarian Study. Journal of Aging Research, 2013, 1–13. doi:10.1155/2013/951786 

4. R. Power et al. (2022) Omega-3 fatty acid, carotenoid and vitamin E supplementation improves working memory in older adults: A randomised clinical trial. Clin Nutr; 41(2):405-414. doi: 10.1016/j.clnu.2021.12.004.