Introduction
Dyslexia is a neurological difference which comes under the umbrella of neurodiversity. Dyslexia can range from mild to severe, with a genetic component, as it often runs in families. Dyslexia has been associated with increased creativity and an enhanced ability to reason, as well as difficulties with reading, writing and sensory and information processing. Individuals with dyslexia may also have difficulties with remembering visual and aural information (1) (2).
Background
Dyslexia is a lifelong condition, and individuals with dyslexia should be supported and celebrated for their unique perspectives and abilities, which are a great strength to society. There are many notable dyslexic individuals making significant contributions to fields such as astronomy, physics, business and the arts (3). However, some research has shown that genetic and environmental factors may play a role in the development of dyslexia, and additionally individuals with dyslexia may have additional requirements for key nutrients, such as omega 3, as well as certain micronutrients such as zinc.
Hypothesised Caused of Dyslexia
Magnocellular Deficit Theory and Noise Exclusion Deficit Theory and Dyslexia
The Magnocellular Deficit Theory of Dyslexia posits that dyslexia occurs following disruption to the Magnocellular system. Magnocellular (M) nerve cells are responsible for the control and visual guidance of eye fixations, and therefore essential for perception and formation of letters and words when reading and writing (4). The Magnocellular Deficit Theory has been scrutinised recently as it does not take into account other factors, such as noise exclusion deficit.
A recent study sought to test the Magnocellular Deficit Theory in a sample of Chinese school children with dyslexia, whilst taking into account noise exclusion deficit. A sample of schoolchildren, with and without dyslexia, were subjected to a variety of reading, writing and aural based assessments, untaken either with no noise or a high noise stimuli in the background. Results indicated that children with dyslexia exhibited a higher threshold to the noise stimuli, supporting the noise exclusion deficit hypothesis. However, the study was unable to further substantiate the magnocellular deficit theory of dyslexia (5)
Genetic Causes of Dyslexia
Some specifically identified genetic variations have been suggested to play a role in the development of dyslexia.
DYX1C1 and DCD2 genes
The DYX1C1 and DCD2 genes are involved in modulating cilia. Cilia are cellular structures with a hair-like appearance, which are present on many cell surfaces, including brain cells. Dysfunctional cilia in the brain have been associated with abnormalities in brain development and function (6) (7). DYX1C1 is involved in motility of cilia, whereas DCD2 modulates length and signalling of cilia. When the functioning of these genes
ATP2C2 gene
The ATP2C2 gene has been hypothesised to be involved in Calcium ion transport, as well as Calcium and Manganese ion homeostasis. This gene has also been theorised to be a major component of various membranes across the body, such as plasma membranes (8). Impaired functioning of ATP2C2 could therefore be a key consideration perhaps for Magnocellular (M) nerve cells in the eyes, disruption of which is implicated in Dyslexia (4), although further research is warranted to explore this further.
KIAA0319 gene and chromosome 18 candidate gene
There is developing research into the role of the KIAA0319 gene, which is hypothesised to have a role in modulating development of magnocellular neurones (9. Regarding genetic variations to the chromosome 18 candidate gene, it has been hypothesised to be involved in the metabolism of omega 3. Therefore a present hypothesis is that individuals with dyslexia with variations to these genes, may have a higher requirement for omega 3 (10). The Dyslexia Research Trust have suggested that increasing omega 3 should be an area of further research to investigate whether it may help to support magnocellular neurone function and therefore improve reading capability in individuals with dyslexia (11).
Nutrition & Lifestyle Interventions
Omega 3
A study measured whole blood fatty acid content of 493 schoolchildren, aged 7–9 years, from mainstream schools in England. They found that lower blood levels of the omega-3 DHA were associated with poorer reading ability and working memory ( 12). A further was conducted where capsules with either fish oil (containing EPA and DHA as well as 20% evening primrose oil) or olive oil were administered to 117 school children aged between 5 and 12, who met the criteria for Developmental Coordination Disorder/Dyspraxia. Results demonstrated that supplementation with fish oil capsules for 3 months was related to an improvement in reading, spelling and behaviour. In this trial, the ratio of omega-3 to omega-6 used in the fish oil capsules was 4:1. Research suggests that the ratio of omega-3 to omega-6 may be important when considering dyslexia (13). Two further studies have suggested that low omega-3:high omega-6 ratios were associated with dyslexia in adults (14) (15).
Key Actions for Increasing Omega 3
Increasing dietary intake of oily fish such as mackerel, salmon, trout or sardines. An omega-3 supplement may help to increase omega-3 levels in the blood as well as increasing overall omega-3 to omega-6 ratio. For vegan and vegetarians, there are many plant based omega 3 supplements available derived from algae.
Side effects: Omega 3 supplements can cause loose stools in sensitive individuals if they are started on too high a dose.
Contraindications with medication: Omega 3 supplements may have a ‘blood-thinning’ effect and should not be mixed with ‘blood thinning’ medication, such as warfarin or heparin.
Zinc
Research suggests that zinc may also be important for learning disorders and cognitive function.
Zinc is a micronutrient vital for the hippocampal region of the brain, which is crucial for memory function. One study found that the zinc levels of children with dyslexia were significantly lower than matched controls without dyslexia (16).
A recent study by indicated that some individuals with dyslexia have a genetic polymorphism on the GRIN2B gene, which is involved in creating a protein present in NMDA receptors of nerve cells as the foetus’ brain develops in utero. NMDA receptors are involved in brain development, learning, memory and synaptic plasticity. The study indicated that zinc levels mediated the expression of the GRIN2B gene (17).
There have been many animal studies into the effects of zinc deficiency, including one which found that rats fed a zinc-deficient diet had significantly impaired learning behaviour. They also reported a decrease in hippocampal size when the zinc-deficient diet was fed for 12 weeks or more (18).
A study of school children found an association between higher dietary zinc intake and increased performance in tests that included memory. Although these findings do not pertain specifically to dyslexia, it does suggest that zinc may be beneficial in managing learning and memory symptoms associated with dyslexia. Further research is needed in this area (19).
Key actions for Increasing Zinc: Shellfish, oysters, red meat, poultry, pumpkin seeds, cashew nuts, beans and legumes are good sources of zinc. Try to include these foods each day in your diet.
Side effects: Some individuals can be allergic to shellfish. Supplemental Zinc, although generally well tolerated, has been associated with adverse side effects like nausea, vomiting, diarrhoea, and stomach pain in some people. It has been suggested that exceeding 40 mg per day of elemental zinc can cause flu-like symptoms like fever, coughing, headache, and fatigue .
Contraindications with medication: zinc supplements can interact with and reduce the effectiveness of many medications, so it is essential to discuss with your doctor before taking zinc supplements.
Selenium
Some preliminary research from China has indicated that children with lower urinary levels of Selenium had a significantly higher risk of developing dyslexia (20). This is an area that really require further research to explore the exact mechanisms involved here.
Key actions for Increasing Selenium: Foods highest in selenium include seafood, organ meats, and Brazil nuts. However, in terms of Western diets, most selenium is obtained from breads, cereals, poultry, red meat, and eggs.
Side effects: Selenium supplements can cause stomach discomfort, headache, and rash. High doses can cause hair loss, fatigue, nausea, vomiting, and weight loss. Extremely high doses can lead to organ failure and death.
Contraindications with medication: Selenium supplements may contraindication with antacids, chemotherapy drugs, corticosteroids, niacin, cholesterol-lowering statin drugs, and birth control pills.
References
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2. British Dyslexia Association, 2022. Available here: https://www.bdadyslexia.org.uk/dyslexia/about-dyslexia/what-is-dyslexia
3. Helen Arkell Dyslexia Charity, 2022. Available here: https://www.helenarkell.org.uk/about-dyslexia.php
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5. Ji, Y., & Bi, H. Y. (2020). Visual Dysfunction in Chinese Children With Developmental Dyslexia: Magnocellular-Dorsal Pathway Deficit or Noise Exclusion Deficit?. Frontiers in psychology, 11, 958. https://doi.org/10.3389/fpsyg.2020.00958
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8. NCBI, 2022. https://www.ncbi.nlm.nih.gov/gene/9914
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