What impact does vitamin D have on multiple sclerosis?

Multiple sclerosis (MS)

Multiple sclerosis is an autoimmune disease. This means that the patient's immune system attacks the body's own cells (the endogenous cells), causing inflammation. In this case, it is the cells of the central nervous system (brain and spinal cord) that are affected.

The central nervous system is the centre of intellectual, cognitive and motor functions (movement, balance, muscle tone, etc.). It is composed of a series of neurons that communicate with each other. Each neuron has an axon: a long fibrous extension that allows it to send information via nerve impulses called action potentials (AP). As in an electrical circuit, the axons need to be isolated so that the nerve impulse reaches the next neuron as quickly as possible. This isolation takes place via the myelin sheath. The APs will "jump" from one myelin segment to another, thus increasing the speed of transmission. In multiple sclerosis, it is this myelin sheath and the cells that produce it (oligodendrocytes) that are attacked by the immune system, thus damaging or preventing message transmission.

This demyelination can affect any segment of the central nervous system, which explains the diversity of symptoms.

Multiple sclerosis evolves following two forms: relapsing-remitting (85% of cases) or progressive (15% of cases).

The former is characterised by successive flare-ups. During these flare-ups, the condition deteriorates and the symptoms worsen. However, after a few days, there is a return to normal with little or no after-effects.

In the progressive form, progression is slow and gradual with or without additional relapses.

Today, research is focused on two main areas: the development of new immunosuppressants and neuroprotection to limit the irreversible damage caused during relapses.

It should be noted that spontaneous repair systems for lesions exist (remyelination). However, they are often insufficient or even non-existent in some patients. Understanding these repair pathways would allow the development of new therapies and is also currently the subject of research.

If you would like to know more about MS, feel free to read our MS fact sheet here.

Vitamin D

By definition, vitamins cannot be produced by the human body, they are only brought in through the diet. However, this is not entirely true for vitamin D. As a matter of fact, vitamin D is a pre-hormone. The body is able to generate it through the skin, thanks in particular to the sun's rays. Vitamin D comes in two forms: D2 (only in plants) and D3 (in plants and animals). These two forms allow, after transformation by the body, to obtain active vitamin D (calcitriol).

Calcitriol has many beneficial properties.

First, vitamin D stimulates intestinal absorption of calcium and phosphorus as well as a normal level of calcium in the blood. Consequently, it promotes growth and maintains strong, healthy bones.

A lack of vitamin D causes softening of the bones, leading to rickets in children and osteomalacia in adults. The latter greatly increases the risk of osteoporosis and fractures.

In developed countries, those most at risk of vitamin D deficiency are alcoholics, people with insufficient sun exposure and those with chronic intestinal disorders (reduced absorption). In addition, vitamin D is fat-soluble. Thus, patients undergoing treatment for obesity or cholesterol (whose aim is to reduce intestinal fat absorption) are also likely to be vitamin D deficient. 

Furthermore, health authorities now recommend that people over 60 years of age should be prescribed vitamin D supplements (between 800 and 1000 IU/day). As a matter of fact, it has been shown that even with a good diet and sufficient sun exposure, the level of vitamin D in this age group is still too low. 

Vitamin D also has an effect on the immune system. It stimulates the cells of innate immunity (macrophages and dendritic cells) as well as adaptive immunity via Th2 lymphocytes (an anti-inflammatory role).

This pre-hormone is therefore prescribed in case of deficiency and for the prevention or treatment, in association with calcium, of osteoporosis and rickets. It is also used as a dietary supplement to stimulate the immune system.

Vitamin D in multiple sclerosis

We now know that vitamin D acts on our immune system. It not only stimulates innate immunity, which is our body's first line of defence, but also adaptive immunity (lymphocytes).

The link between vitamin D and multiple sclerosis was first established because of the higher prevalence of the disease in regions of the world with low levels of sunlight. Additionally, observational studies suggest that during the winter months patients experience more relapses. 

Furthermore, when sun exposure increased, the progression after an episode of CIS (clinically isolated syndrome) suggestive of MS to MS decreased.

In cell and animal experiments, researchers have observed that vitamin D reduces the action of pro-inflammatory T cells. In addition, it stimulates regulatory T lymphocytes (Tregs), which are involved in autoimmune syndromes. In humans, a deficit in Tregs is associated with numerous autoimmune diseases. 

However, these hopes must be tempered. Indeed, high levels of Tregs have been observed in the injured tissues of patients with multiple sclerosis, rheumatoid arthritis and psoriasis. This suggests that the Tregs deficit in these inflammatory syndromes is functional and not quantitative. 

In addition, the link between a favourable disease course and vitamin D supplementation has not yet been clearly demonstrated. According to the Multiple Sclerosis Society of Canada, four studies did not show a significant therapeutic change compared to placebo. According to the same entity, five studies have shown improvement (measured in number of relapses and number of brain lesions), although the benefits vary between studies.

In summary, at present, vitamin D deficiency is associated with an increased risk of developing multiple sclerosis. However, no therapeutic effect between calciferol supplementation and a positive outcome in MS has yet been demonstrated. Studies are still ongoing.    

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