COGNITION

CAROTENOIDS ENHANCE COGNITIVE HEALTH AND FUNCTION

Cognition

The brain is a physical organ and core part of the central nervous system. Cognition refers to the mental process that the brain uses to acquire information and understanding through thoughts, experiences and the senses. Our cognitive abilities can be broadly classified into two groups: crystalized and fluid abilities. Crystallized abilities refer to skills and memories that we have acquired over our lifetime e.g. general knowledge, vocabulary. Fluid abilities refer to our capacity to process, manipulate and transform information to complete a task at a point in time e.g. problem-solving, reasoning.

Cognition can also be divided into specific domains such as memory, perception, language, decision-making, planning and reasoning.

As we age, some cognitive domains such as speech, language and procedural memory (e.g. remembering how to play the piano) will remain stable while other domains such as prospective memory (e.g. remembering to perform a specific action in the future) and executive function (e.g. multi-tasking or planning) will decline with increasing age. Different parts of the brain are affected differently by age and some regions (e.g. the prefrontal lobe, which is responsible for decision making; and the hippocampus, which is involved in short- and long-term memory and spatial memory) are affected more than others (e.g. the occipital lobe, which is important for visual function). When initial age-related changes occur, our brain is able to compensate (e.g. by using additional brain regions and neural circuitry) and this enables us to continue to function normally. However, as neuronal damage increases (due to a variety of reasons ranging from genetics to life events), our brain can no longer compensate for these changes and we begin to show subtle cognitive decline. This reduces the efficiency and effectiveness of neurons to communicate to one another and leads to signs and symptoms of cognitive decline.

Carotenoids and the Brain

A number of carotenoids (nutrients) have been identified in brain tissue including the hippocampus, cerebellum, and frontal, occipital, and temporal cortices.[1] Lutein is the most concentrated xanthophyll carotenoid in the brain and so much of the research that has been completed to date involves this nutrient. Research by the Nutrition Research Centre Ireland (NRCI) has shown that patients with Alzheimer’s disease are deficient in serum carotenoid lutein and zeaxanthin concentrations and macular pigment levels (see below).[2, 3]

Macular Pigment and the Brain

The carotenoids lutein, zeaxanthin and meso-zeaxanthin are preferentially concentrated in the central retina (which is part of the central nervous system) where they are collectively referred to as macular pigment. Interestingly, macular pigment levels correlate positively and significantly with brain concentrations of lutein and zeaxanthin.[4] Therefore, the measurement of macular pigment can be used as a non-invasive clinical biomarker of brain nutrition and potentially of cognitive health, given that higher macular pigment levels have been associated with better cognitive performance in both healthy and cognitively impaired individuals.

Carotenoids and Cognition

Population-based studies have shown that higher concentrations of carotenoids (measured in blood and from questionnaires) are associated with better cognitive performance in healthy individuals.[5-7] Higher consumption of green leafy vegetables (rich in the xanthophyll carotenoid lutein) in particular has shown to be significantly related to slower rates of cognitive decline in cognitively healthy individuals. Interestingly, studies have shown that carotenoid concentrations are lower in individuals with cognitive impairment in comparison to cognitively healthy individuals.

When carotenoids are consumed by healthy individuals in high concentrations (i.e. from nutritional supplements), studies have found improvements in a number of cognitive domains including attention, episodic memory (e.g. remembering where you parked your car in a multi-story car park), processing speed and reaction time.[8] To date, no improvements in cognition have been observed among patients with Alzheimer’s disease following carotenoid supplementation, suggesting that earlier nutritional intervention is important. However, pilot work by the NRCI has shown improvements in quality of life (mood, memory and vision) of patient with Alzheimer’s disease following supplementation with carotenoids and omega-3 fatty acids.[9] A

Function of Carotenoids
in the Brain

Research is ongoing in order to fully understand the relationship between carotenoids and brain health. However, advances in science and technology have increased our capacity to fully understand the unique neuroprotective mechanisms of carotenoids that are likely to be driving the positive results that have been observed. The suggested neuroprotective properties of carotenoids are likely due to the chemical structure of the carotenoids, their locations within cells and their lipid solubility. 

These neuroprotective properties include:

Reducing oxidative stress
Carotenoids are powerful antioxidants and so they can reduce levels of oxidative damage. This is likely due to the chemical structure of the carotenoids, their locations within cells and their lipid solubility.

Reducing neuro-inflammation
Carotenoids also play a role in reducing inflammation of the nervous tissue (i.e. neuro-inflammation) by modulating inflammatory cells and pro-inflammatory enzymes, and down-regulating the production of pro-inflammatory molecules and inflammatory gene expression.

Positively affect the structural properties of membranes
Carotenoids can also affect the structural and dynamic properties of the membranes (e.g. thickness, permeability). For example, it has been suggested that the xanthophyll carotenoid lutein can facilitate the transfer of compounds (e.g., molecules or nutrients) from one cell to another.

Improve neural efficiency
It has also been shown that the xanthophyll carotenoids lutein and zeaxanthin can positively impact neural efficiency, whereby individuals with higher levels of these xanthophyll carotenoids required less brain power to complete the same tasks as individuals with lower levels of these carotenoids.

Reference List

1. Johnson, E.J., et al., Relationship between Serum and Brain Carotenoids, alpha-Tocopherol, and Retinol Concentrations and Cognitive Performance in the Oldest Old from the Georgia Centenarian Study. J Aging Res, 2013.

2. Nolan, J.M., et al., Macular Pigment, Visual Function, and Macular Disease among Subjects with Alzheimer’s Disease: An Exploratory Study. Journal of Alzheimer’s Disease, 2014.

3. Nolan, J.M., et al., The impact of supplemental macular carotenoids in Alzheimer’s disease: a randomized clinical trial. J Alzheimers Dis, 2015. 44(4): p. 1157-69.

4. Johnson, E.J., et al., Relationship between serum and brain carotenoids, alpha-tocopherol, and retinol concentrations and cognitive performance in the oldest old from the Georgia Centenarian Study. J.Aging Res., 2013. 2013: p. 951786.

5. Feeney, J., et al., Low macular pigment optical density is associated with lower cognitive performance in a large, population-based sample of older adults. Neurobiol Aging, 2013. 34(11): p. 2449-56.

6. Feeney, J., et al., Plasma Lutein and Zeaxanthin Are Associated With Better Cognitive Function Across Multiple Domains in a Large Population-Based Sample of Older Adults: Findings from The Irish Longitudinal Study on Aging. J Gerontol A Biol Sci Med Sci, 2017. 72(10): p. 1431-1436.

7. Vishwanathan, R., et al., Macular pigment optical density is related to cognitive function in older people. Age Ageing, 2014. 43(2): p. 271-275.

8. Power, R., et al., Supplemental Retinal Carotenoids Enhance Memory in Healthy Individuals with Low Levels of Macular Pigment in A Randomized, Double-Blind, Placebo-Controlled Clinical Trial. J Alzheimers Dis, 2018. 61(3): p. 947-961.

9. Nolan, J.M., et al., Nutritional Intervention to Prevent Alzheimer’s Disease: Potential Benefits of Xanthophyll Carotenoids and Omega-3 Fatty Acids Combined. J Alzheimers Dis, 2018. 64(2): p. 367-378.