Vitamin D Supplementation

Why Is Vitamin D Important for MS?

• Immune system support: MS is an autoimmune condition where the immune system mistakenly attacks the protective covering of nerves. Vitamin D helps regulate immune responses and may reduce inflammation.
• Lower MS risk and activity: Several studies have found that people with higher blood levels of vitamin D have a lower risk of developing MS. For those already diagnosed, higher levels may be associated with fewer relapses and slower disease progression.
• Common deficiency: Many people with MS have low levels of vitamin D, especially those living in areas with little sunlight, darker skin tones, or limited sun exposure. This makes supplementation an important consideration.

However, it isn’t always easy for us to get vitamin D from a natural sunlight source, so we need to turn to supplements to stay in a healthy range all year round.

Vitamin D Supplement Formats Available

Vitamin D supplements come in various forms to suit different preferences and needs:

• Capsules or tablets – the most common form.
• Drops or sprays – useful for people who have trouble swallowing pills.
• Combined supplements – often paired with calcium or magnesium.
• High-dose prescriptions – sometimes used for short-term correction of deficiency, under medical supervision.

While vitamin D is essential, more isn’t always better. Taking very high doses without monitoring can lead to vitamin D toxicity, which may cause nausea, kidney problems, or calcium imbalance. Regular blood tests can help ensure your levels stay within a safe, effective range.

Talk to your doctor or MS nurse before starting any supplement. They can help you decide what’s right for your personal health and MS management plan.

How much vitamin D supplementation do I need?

We recommend testing your vitamin D levels to understand your current levels before making any further decision.

If levels are very low, a one-off ‘megadose’ of vitamin D3 may be offered by your healthcare professional to quickly restore levels, followed by regular daily supplementation.

General recommendations:

• A healthy vitamin D level is thought to be between 100–150 nmol/L.
• There is no single ‘good for everyone’ dose, but common recommendations include:
  • 4,000 units per day – a common amount recommended by UK neurologists.
  • 6,000–10,000 units per day – may be needed to maintain optimal levels.

The world of Vitamin D and other supplements podcast

Listen to this podcast on the world of vitamin D and supplementation with Dr Conor Kerley – an expert in his own right on this topic.

Vitamin D2 vs. D3: what’s the difference?

Vitamin D comes in two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). They are found here:

• Vitamin D2: Found in plant-based sources like mushrooms (especially those exposed to UV light) and fortified foods (such as cereals and plant-based milk).
• Vitamin D3: Found in animal-based sources like fatty fish (salmon, mackerel), fish liver oils, egg yolks, and dairy products. It is also produced naturally in the skin when exposed to sunlight (UVB rays).

Vitamin D3 is more bioavailable than vitamin D2, meaning it is absorbed and used more efficiently by the body. Bioavailability refers to how much of a substance actually gets into your bloodstream and is available for your body to use. A nutrient with higher bioavailability is absorbed more effectively and stays in the body longer, making it more beneficial – vitamin D3 was found to be 40% more effective than D2 at raising overall vitamin D levels. This is because:

1. Vitamin D3 lasts longer in the body
2. D3 is more easily converted into the active form
3. D3 binds better to vitamin D receptors

Are vitamin D megadoses safe?

Yes – taking megadoses under medical supervision is perfectly safe as a once-off, and there is a comfortable margin of safety. The potential risk from particularly large doses of vitamin D is that your blood calcium levels can rise, potentially leading to other problems.

Serious side effects are rare but taking excessive doses over a long period can lead to high calcium levels in the blood (hypercalcaemia). This is usually only seen in extreme cases, such as people taking 130,000 units per day for 20 months, which is far beyond any recommended dosage.

To stay safe, monitor your vitamin D levels regularly and consult a healthcare professional before taking very high doses.

Are vitamin D supplements safe during pregnancy?

Vitamin D is naturally occurring nutrient manufactured by skin when exposed to sunlight (UVB). It is safe to continue taking vitamin D during pregnancy (and when breast feeding). In the UK the NHS recommended all pregnant and breastfeeding women take vitamin D supplements.

You may be tested by your doctor during your pregnancy if you are in an at risk group for vitamin D deficiency – this includes women with MS. Make sure that you check the amount of vitamin D in any prenatal vitamins you are taking, and factor this in with your vitamin D dosage.

A randomised controlled trial found that vitamin D3 supplementation of up to 4,000 IU per day during pregnancy was safe. In the study, supplementation began between 12 and 16 weeks of pregnancy.

Can I use a sunbed to get my vitamin D?

We strongly recommend that you do not use a sunbed to increase your vitamin D levels due to the risk of unnecessary skin damage and skin cancer. There is no safe level of sunbed use.