Do antioxidants protect against dementia?

Aging


Although the increase in life expectancy is one of the key achievements of modern societies, degenerative diseases are becoming more prevalent. Dementia is one of the most common age-related chronic diseases. Approximately 47 million people were affected by dementia worldwide in 2015 and this number is predicted to double every 20 years.1

Dementia includes disorders characterised by loss of cognitive functioning, such as thinking, remembering, and reasoning, and by impairment of behavioral abilities to the extent that daily life activities are compromised.2 Alzheimer’s disease is the most common form of dementia and is the third most expensive disease in the United States after cancer and coronary heart disease. Treatment and prevention of dementia have long been considered impossible.

The cause of dementia is multifactorial and risk factors include vascular disease, obesity, and diabetes mellitus. Emerging evidence suggests that certain lifestyle choices are related to reduced risk, and that modification of lifestyle factors could promote healthy aging.

In addition to risk factors, protective factors are increasingly receiving attention, including antioxidants. Natural antioxidants could be valuable weapons in the fight against dementia due to their effects in multiple pathways, through which oxidative stress leads to neurodegeneration and triggers neuroinflammation.

Oxidative stress is an imbalance between the production and accumulation of oxygen reactive species (ROS) in cells and tissues. The nervous system is particularly vulnerable to oxidative stress as it uses lots of oxygen for energy, has high levels of unsaturated fatty acids and relatively low levels of antioxidants.3

Higher antioxidant levels are linked to a reduced risk of developing dementia

Evidence from experimental data suggests that antioxidants may protect against neurodegeneration by influencing early stages of dementia development.

A variety of substances can act as antioxidants, including vitamin C, vitamin E, beta-carotene and other related carotenoids, flavonoids, and phenols, to prevent the overproduction of ROS.

Vitamin E

Vitamin E occurs naturally in the diet and can be found in a variety of foods, including vegetable oils and fats, nuts, and seeds.

Higher intake of foods rich in vitamin E may modestly reduce long-term dementia risk. A study published in Archives of Neurology found that participants in the highest tertile of vitamin E intake were 25% less likely to develop dementia than those in the lowest tertile.4

However, other evidence suggests that there are neither benefits or harms from vitamin E supplementation. Certain studies found that vitamin E intake did not lead to any differences in dementia development or in improving cognition (learning and memory) in people with Alzheimer’s disease.5

Flavonoids

Flavonoids are powerful antioxidant substances contained in fruits, vegetables, wine, cocoa, and tea. A study published in the European Journal of Epidemiology found that a higher intake of antioxidant flavonoids results in a reduced risk of incident dementia.6

Carotenoids

New research suggests that the most important antioxidants for brain protection may be the carotenoids lutein plus zeaxanthin and beta-cryptoxanthin. A recent study published in Neurology examined the relationship between the antioxidants lutein and zeaxanthin and beta-cryptoxanthin and the likelihood of developing dementia.7

Carotenoids are converted by the body into vitamin A. The carotenoids lutein and zeaxanthin are found in green, leafy vegetables, such as kale, spinach, broccoli, and peas. Beta-cryptoxanthin is found in fruits, such as oranges, papaya, tangerines, and persimmons.

The study involved 7,283 dementia-free people who were at least 45 years old at the beginning of the study. They had a physical exam, interview, and blood tests for antioxidant levels at the start of the study. They were then followed for an average of 16 years to see who developed dementia. The results showed that people with the highest levels of lutein and zeaxanthin and beta-cryptoxanthin in their blood were less likely to develop dementia decades later than people with lower levels of these antioxidants.

The author of this study, Dr May Beydoun, stated, “Extending people’s cognitive functioning is an important public health challenge. Antioxidants may help protect the brain from oxidative stress, which can cause cell damage. Further studies are needed to test whether adding these antioxidants can help protect the brain from dementia.”8

A limitation of this study was that antioxidant levels were based on one measurement of blood levels, which may not reflect people’s levels over their lifetime. A long-term, randomised clinical trial is required to test the effect of antioxidant supplements on the development of dementia.

More research is also required into which antioxidants are the most beneficial for reducing dementia risk due to conflicting results. Understanding the relationship between antioxidants and dementia could help in the process of diagnosing dementia earlier, as it still occurs far too late.

There is growing evidence that a balanced diet, as part of a healthy lifestyle, is beneficial in delaying age-related diseases and dementia. Fruits and vegetables are considered to be the best source of antioxidant micronutrients.9

References:

1. Perneczky R. (2019). Dementia prevention and reserve against neurodegenerative disease. Dialogues Clin Neurosci, 21(1): 53–60. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6780359/

2. Sancesario G and Bernardini S. (2018). Diagnosis of neurodegenerative dementia: where do we stand, now? Ann Transl Med, 6(17): 340. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6174181/

3. Jurcau A. (2021). The role of natural antioxidants in the prevention of dementia – where do we stand and future perspectives. Nutrients, 13(2): 282. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7909256/

4. Devore E, et al. (2010). Dietary antioxidants and long-term risk of dementia. Arch Neurol, 67(7): 819–25. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2923546/

5. Farina N, et al. (2017). Vitamin E for Alzheimer’s dementia and mild cognitive impairment. Cochrane Database Syst Rev, 1(1). Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6464807/

6. Commenges D, et al. Intake of flavonoids and risk of dementia. Eur J Epidemiol, 16(4): 357–63. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/10959944/

7. Beydoun M, et al. (2022). Association of serum antioxidant vitamins and carotenoids with incident Alzheimer disease and all-cause dementia among US adults. Neurology, 98(21): e2150–62. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/35508396/

8. Higher antioxidant levels linked to lower dementia risk (2022). EurekAlert! Retrieved from: https://www.eurekalert.org/news-releases/951218

9. Polidori M and Schulz R-J. (2014). Nutritional contributions to dementia prevention: main issues on antioxidant micronutrients. Genes Nutr, 9:382. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3968291/

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