Myelin is an insulating layer that forms around nerves in the body. It is made up of protein and fatty substances and helps signals travel quickly along nerve fibers. Damage to myelin, called demyelination, can cause problems with sensation, movement, cognition, and other functions depending on the nerves affected. Multiple sclerosis is one disease characterized by myelin destruction. Researchers are investigating whether vitamin D may help repair or protect myelin.
What is myelin?
Myelin is a fatty substance that wraps around nerve axons in the central nervous system, acting as an insulator. This allows electrical impulses to transmit quickly and efficiently along nerve cells.
Myelin is formed by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. These cells wrap specialized membrane layers around axons, compacting and stacking them to form the myelin sheath.
Functions of myelin
Myelin serves several important functions:
– Speeds transmission of signals – Signals can propagate along myelinated axons at speeds up to 100 times faster than unmyelinated axons. This allows for faster communication between neurons.
– Insulates axons – Myelin acts as an electrical insulator for axons, preventing current from leaking out and allowing impulses to travel further distances.
– Provides trophic support – Myelin contains trophic factors that help nourish neurons and promote their survival.
Structure of myelin
The structure of myelin is optimized to provide insulation and speed signaling. It consists of:
– Compact lipid layers – Myelin contains 70-85% lipid material, including cholesterol and galactolipids. These form dense, hydrophobic layers.
– Myelin proteins – Proteins like proteolipid protein and myelin basic protein hold the layers together and mediate interactions.
– Regions without myelin (nodes of Ranvier) – Gaps between myelinated segments allow impulses to “hop” from node to node.
This compact, discontinuous structure maximizes speed of signaling.
What causes myelin damage?
Myelin damage, called demyelination, has several potential causes:
Autoimmune diseases
In autoimmune disorders like multiple sclerosis, the immune system mistakenly attacks myelin as foreign. This triggers inflammation and stripping of the myelin layers.
Infections
Viruses like Epstein-Barr, herpes simplex, and others can infect and kill oligodendrocytes, destroying myelin.
Toxins
Toxins like mercury that build up in the body can damage myelin over time.
Trauma
Injury to the spinal cord can sever myelinated axons and cause acute demyelination.
Poor nutrition
Deficiencies in vitamins and minerals needed to build myelin, like vitamin B12, can lead to demyelination.
Neurodegenerative diseases
Diseases like Alzheimer’s and Parkinson’s damage myelin through mechanisms involving tau proteins and alpha-synuclein.
Aging
Myelin often weakens and deteriorates with advanced age. Breakdown outpaces remyelination.
Consequences of demyelination
Demyelination impairs nerve signaling and can lead to a variety of neurological symptoms:
– Slow nerve conduction – Unmyelinated fibers transmit signals much slower, impairing function
– Impaired sensation – Damage to sensory tracts diminishes touch, pain, vibration sense
– Weakness – Motor tract damage weakens muscles
– Cognitive problems – Demyelination in the brain affects cognition and memory
– Fatigue – Nerve signaling problems lead to greater fatigue
– Bladder/bowel dysfunction – Autonomic nerves controlling these systems can be affected
Exactly which functions are impaired depends on the location of demyelination in the central or peripheral nervous systems.
Does the body naturally repair myelin?
The body has some capacity to repair myelin through a process called remyelination:
– Myelinating cells proliferate and migrate to demyelinated areas
– They wrap new myelin layers around damaged axons
– Nodes of Ranvier are reformed, restoring fast signaling
However, remyelination becomes less efficient with age and repeated demyelinating insults. Remyelinated sheaths are thinner and shorter than original myelin.
Research into enhancing natural remyelination is ongoing, looking at approaches like boosting myelinating cell proliferation and recruitment.
What is vitamin D and what does it do in the body?
Vitamin D is a fat-soluble vitamin that has several key functions in the body:
– Aids calcium absorption – Vitamin D helps the body utilize calcium from food to maintain strong bones.
– Regulates immune function – Vitamin D modulates both innate and adaptive immunity and helps regulate autoimmune responses.
– Supports cell growth – It controls proliferation and differentiation of various cell types.
– Reduces inflammation – Vitamin D exhibits anti-inflammatory properties.
– Protects neurons – It helps clear toxins and prevent oxidative damage in neurons.
There are two main forms of vitamin D:
– Vitamin D3 (cholecalciferol)
– Vitamin D2 (ergocalciferol)
Vitamin D3 is produced in the skin through sun exposure, while both D2 and D3 can be obtained from foods and supplements.
Vitamin D sources
Sources of vitamin D include:
– Sunlight – Skin exposure to UVB radiation
– Oily fish – Salmon, tuna, mackerel
– Supplements – Vitamin D2 or D3 pills and drops
– Fortified foods – Milk, cereals, orange juice
– Mushrooms – Both wild and UV-treated mushrooms
Factors affecting vitamin D levels
Levels of vitamin D are influenced by:
– Sun exposure – More exposure means more vitamin D production
– Skin pigment – Darker skin inhibits vitamin D synthesis
– Age – Production declines with age
– Body fat – Vitamin D is stored in fat, making it less bioavailable in obesity
– GI absorption -Digestive issues reduce vitamin D absorption
– Kidney function – Kidneys activate vitamin D, so kidney disease reduces active levels.
Many people are deficient in vitamin D, especially in winter at higher latitudes.
How might vitamin D help repair myelin?
Researchers are investigating several ways vitamin D may help protect or repair myelin:
1. Reducing inflammation
Vitamin D helps regulate immune responses. It may suppress inflammatory cytokines and immune attacks on myelin:
– Reduces TNF-alpha, IL-6, IL-17 expression
– Raises anti-inflammatory cytokines like IL-10
– Inhibits T cell and B cell proliferation
– Lowers autoantibodies against myelin
2. Supporting oligodendrocyte health
Oligodendrocytes produce and maintain myelin. Vitamin D may:
– Enhance oligodendrocyte progenitor cell proliferation
– Promote oligodendrocyte differentiation and maturation
– Protect oligodendrocytes from oxidative stress
3. Regulating calcium signaling
Calcium signals stimulate myelin generation. Vitamin D:
– Helps maintain optimal calcium concentrations
– May regulate channels and receptors involved in calcium signaling in oligodendrocytes
4. Antioxidant effects
Oxidative stress damages myelin. Vitamin D may reduce reactive oxygen species and upregulate antioxidant enzymes.
5. Neuroprotective effects
Vitamin D protects neurons from toxins and apoptosis. Protecting axons may help preserve myelin.
6. Stimulating neurotrophic factors
Vitamin D increases neurotrophins like NGF, NT-3, and GDNF that support myelinating cells.
7. Epigenetic effects
Vitamin D interacts with receptors on DNA that control gene expression for myelination.
8. Improving mental health
Vitamin D supplementation has mental health benefits, which could improve motivation for rehab in MS patients.
What does the research say?
Multiple studies suggest vitamin D may help protect and repair myelin:
Animal studies
– Boosting vitamin D reduced EAE severity in mice, a model of MS. Less myelin loss occurred.
– Vitamin D deficient rats developed more myelin damage and oligodendrocyte loss.
– Mice genetically engineered to have elevated vitamin D were more resistant to EAE with less demyelination.
Human studies
– MS patients with lower vitamin D levels had higher disease activity on MRI scans.
– Children with higher vitamin D intake were less likely to develop MS later in life.
– MS progression slowed in patients who normalized vitamin D levels with supplementation.
– Fewer new MS lesions and relapses occurred with vitamin D supplementation.
– Higher maternal vitamin D levels during pregnancy reduced later MS risk in offspring.
However, some studies show no benefit of vitamin D supplementation on MS disease course. Larger, longer trials are still needed.
Mechanistic studies
– Vitamin D stimulated maturation of oligodendrocyte precursor cells in human cell cultures.
– It promoted expression of myelin genes and proteins in rodent oligodendrocytes.
– MS patients had fewer T cells secreting inflammatory cytokines after vitamin D supplementation.
What are the best sources of vitamin D?
The best ways to obtain vitamin D are:
Sunlight
– Exposing skin to direct sunlight triggers vitamin D synthesis.
– About 10-15 minutes of sun exposure on arms and legs a few times a week is adequate.
– Don’t overdo it – too much sun exposure doesn’t increase vitamin D much more and can raise skin cancer risk.
Fatty fish
– Salmon, tuna, mackerel are high in vitamin D.
– Aim for at least 2 servings of fatty fish per week.
– Cooking does not destroy vitamin D in fish.
Supplements
– Vitamin D3 (cholecalciferol) supplements are widely available.
– Cod liver oil also supplies vitamin D.
– Check labels for dosage – adults need at least 600-800 IU per day.
Fortified foods
– Products like milk, orange juice, yogurt, cereals are fortified with vitamin D.
– Check nutrition labels for percentage daily value.
– Fortification levels can vary between brands.
Mushrooms
– Both UV-treated and wild mushrooms have vitamin D.
– Shiitake and maitake mushrooms have the most naturally.
– Exposure to sunlight boosts D levels in all mushrooms.
What is the recommended daily intake?
The recommended daily vitamin D intake is:
– Infants: 400 IU
– Children 1-18 years: 600 IU
– Adults up to age 70: 600 IU
– Adults over 70: 800 IU
– Pregnant/breastfeeding women: 600 IU
However, many experts believe these are too low. Optimal blood levels are above 30-40 ng/mL. Most people need 1000-4000 IU per day to reach ideal levels, especially those with little sun exposure.
Too much vitamin D over 10,000 IU daily can cause toxicity with hypercalcemia and kidney stones. Have levels monitored by a doctor if supplementing high doses.
Should vitamin D be used to treat MS?
There is not yet sufficient evidence to definitively recommend vitamin D to treat MS. However:
– Normalizing vitamin D deficiency is reasonable given the potential benefits and low risk.
– Many MS specialists test levels and recommend supplementation if low, especially early in disease.
– Most focus on maintaining sufficient levels rather than mega-dosing. 1,000-4,000 IU per day is common.
– Vitamin D supplements likely have benefits for overall health beyond any potential impact on MS.
– Larger clinical trials of vitamin D for treating MS progression and symptoms are underway.
More research is still needed, but optimizing vitamin D intake may be advantageous for MS until stronger evidence emerges. Patients should discuss supplementation with their neurologist.
Can vitamin D reverse myelin damage?
It’s unlikely vitamin D can fully reverse existing myelin damage on its own. However, by stimulating remyelination, it may help partially repair and mitigate the effects of demyelination by:
– Boosting new myelin formation by oligodendrocytes.
– Improving thickness and integrity of newly forming myelin sheaths.
– Increasing number and length of myelin segments on demyelinated axons.
– Speeding up remyelination rate and efficiency after immune attacks.
– Reducing damage from future attacks by suppressing inflammation.
– Protecting vulnerable neurons and axons from further injury.
– Enhancing nerve conduction through regenerating myelin.
While not directly reversing damage, vitamin D may facilitate endogenous regeneration and lessen the functional impact of myelin loss.
Are there risks or side effects?
Vitamin D is generally safe at recommended dosages, but there are some potential side effects to be aware of:
– Hypercalcemia – Excessively high vitamin D levels can raise blood calcium. This can cause nausea, vomiting, confusion, kidney stones, arrhythmias.
– Hypercalciuria – Too much vitamin D leads to excess calcium in the urine, which may cause kidney stones.
– Hyperphosphatemia – High blood phosphate is another possible effect of vitamin D excess.
– GI distress – Nausea, vomiting, diarrhea, constipation, poor appetite with high doses.
– Muscle weakness – Seen occasionally with very high vitamin D intake.
To prevent side effects:
– Don’t exceed 10,000 IU daily without close monitoring.
– Have vitamin D blood level tested if supplementing high doses.
– Maintain adequate calcium and hydration when supplementing.
– Reduce dose if experiencing any symptoms of excess.
Overall, vitamin D is very safe if intake guidelines are followed and levels are monitored.
Are there any drug interactions?
The main drugs that interact with vitamin D include:
– Corticosteroids – These reduce vitamin D levels. Supplementation may be needed with chronic steroid use.
– Seizure medications – Vitamin D can either reduce or increase levels of anticonvulsants. Monitoring levels is important.
– Digoxin – Excess vitamin D can increase risk of digoxin toxicity.
– Diuretics – Loop diuretics and thiazides increase calcium excretion, altering vitamin D needs.
– Weight loss drugs – Orlistat reduces vitamin D absorption.
– Cholesterol drugs – Cholestyramine and colestipol can decrease vitamin D levels.
– Antibiotics – Isoniazid, Rifampin, anti-TB drugs speed up vitamin D metabolism.
Check with both pharmacist and doctor when taking vitamin D with medications. Dosage adjustments or monitoring may be required.
Takeaways
– Myelin is an insulating layer around nerves essential for proper functioning.
– Demyelination causes neurological impairment in diseases like MS.
– Vitamin D exhibits immunomodulatory and neuroprotective effects that may help repair myelin.
– Human studies show links between vitamin D levels and MS risk and progression.
– Optimizing vitamin D status may support remyelination, but definitive evidence is still lacking.
– When supplementing vitamin D, have levels monitored and watch for potential side effects.
– More research is underway to determine vitamin D’s therapeutic role in treating demyelinating conditions.
Conclusion
While vitamin D is unlikely to fully reverse existing myelin damage, growing evidence suggests it may help protect and repair myelin through anti-inflammatory and neuroprotective mechanisms. Many MS specialists now routinely check vitamin D levels and recommend supplementation to help maintain optimal status, especially early in the disease course. However, larger clinical trials are still needed to conclusively determine if vitamin D has a disease-modifying role in MS. In the meantime, patients should discuss checking vitamin D levels and supplement options with their doctor, as maintaining sufficient levels is advisable for overall health. With close monitoring, vitamin D supplementation appears relatively safe and promising for mitigating myelin damage from autoimmunity, infection, aging and other causes.