Vitamin D for immune health: key nutrients to boost immune health in ME/CFS and Long Covid

When you have ME/CFS, Long Covid or Fibromyalgia, your immune function is compromised, a feature of these conditions.  However, you can take action to support your immune system and there are practical steps you can take to make your immune function as strong as possible. If you are deficient in Vitamin D this is likely to further weaken your immune health – so we recommend you get tested and optimise your Vitamin D. We also recommend you consider two other important nutrients which support resilience to infection – Vitamin C and Zinc.

Here we describe why these key nutrients are so important for immune health, especially if you have ME/CFS, Long Covid or Fibromyalgia, and outline practical steps you can take to make sure you meet optimal levels of these nutrients.

1.   Supporting your immune health with Vitamin D

Why vitamin D matters in ME/CFS, Long Covid, and Fibromyalgia

Vitamin D activates immune cells (T cells, B cells, macrophages) and regulates their activity. It boosts antimicrobial defences while dampening excessive inflammation — crucial when immune dysregulation drives symptoms.

Vitamin D also helps to control inflammation - it reduces pro-inflammatory cytokines (IL-6, TNF-α) and increases anti-inflammatory cytokines (IL-10).

Vitamin D also supports barrier protection – it supports lung and gut lining integrity, reducing infection risk.

What the research shows

Long Covid – many studies show that patients with long Covid have lower vitamin D levels compared to those who recovered fully. Deficiency correlates with fatigue, brain fog, palpitations, and depression

ME/CFS - research suggests vitamin D status is linked to inflammation, oxidative stress, and vascular function, even if not all patients show outright deficiency

Fibromyalgia - low vitamin D are linked to higher levels of pro-inflammatory cytokines and more severe pain symptoms. Recent studies also link it to altered gut microbiota metabolism and chronic inflammatory pain

How we get vitamin D – why we need sunshine!

Supporting your immune health with vitamin D is really important. So how do we achieve this? There are two routes to getting vitamin D:

Foods such as oily fish (salmon, mackerel, sardines), egg yolks, liver and mushrooms may provide us with some Vitamin D, these foods cannot provide sufficient to meet our Vitamin D requirements.

Sunshine - we get most of our vitamin D through exposure of our skin to the sun in the summer months.

We recommend the following:

Between April–September (UK) -  expose arms/legs/face for 15–30 minutes, 2–3 times per week between. For exposure to the important UVB rays from the sun, this exposure needs to be between 10 am –3 pm.

Darker skin -  if you have darker skin, you will need to have longer exposure, and are likely to need 30–60+ minutes of exposure 2-3 times each week

Between October–March we cannot make enough vitamin D from the sun in the UK as the sun is too low in the sky and therefore we cannot get enough exposure to UVB rays. We therefore all need to take a vitamin D supplements during these months.

If you are unable to get outside a great deal during the summer months - it is recommended you take a vitamin D supplement throughout the year.

Practical steps for optimal vitamin D in the Winter months

a) Get your vitamin D blood levels tested

• Ask your GP if they will test your Vitamin D levels using a 25(OH)D blood test

• If this is not possible, you may prefer to use a private testing service – but be careful as the quality of some tests is not very good and don’t give you enough detail on you blood levels. One option is to use a private test provided by the NHS, such as the Black Country Pathology Services, which costs £31

Optimal blood levels of vitamin D

If you have a vitamin D blood ( serum) test you can check whether you are deficient or not:

Aim for at least 75 nmol/L for optimal immune and musculoskeletal health (above the NHS “adequate” threshold of 50 nmol/L).

b) Take a Vitamin D supplement between October and the end of March

The NHS recommends that we all take a vitamin D supplement between October and March each year - at a minimum 400IU (10mcg) per day is recommended

c) If your blood levels show you are deficient in Vitamin D

If your blood test shows you are deficient in vitamin D you will need to take a higher dose of vitamin D supplement on a temporary basis. For example, a GP or healthcare professional may recommend 3000–4000 IU/ vitamin D per day for 3 months, or they may prescribe a loading dose such as 25,000 IU for several days. Levels should be retested before returning to a daily maintenance dose

d) Choose the right vitamin D supplement

• Oil based supplement - Vitamin D is a fat-soluble vitamin, so it is better to take it in capsule/spray form suspended in oil. If tablets are used. eat with a meal containing fat

• Vitamin D3 (cholecalciferol)   -  vitamin D3 is more effective at raising and maintaining blood vitamin D levels than vitamin D2 (ergocalciferol)

• Dose - 1000 IU/day (25mcg) is a common maintenance dose.  only use doses over 4000iu on a temporary basis if advised, if deficiency is identified

e) Nutrients to take alongside vitamin D to improve effectiveness

There are two important nutrients that work with Vitamin D:

a) Vitamin K2

It is good to take a supplement which combines vitamin D and vitamin K because:

Vitamin D increases calcium absorption - Vitamin D helps the gut absorb calcium from food and supplements which raises the amount of calcium circulating in the blood

Vitamin K directs calcium to the right places - Vitamin K2 activates specific proteins that bind calcium and move it into bones and teeth. These proteins help prevent calcium from being deposited in blood vessels and soft tissues - which could contribute to stiffness or calcification

Vitamins D and K2 work together for bone and heart health - without enough vitamin K2, higher calcium from vitamin D might not be used efficiently for bone building. Vitamin D plus vitamin K2 may be more effective (and safer) than vitamin D alone for supporting bone strength and vascular health

Warning:

Do not take vitamin K2 supplements if you are on warfarin or similar anticoagulants, unless specifically directed by your doctor

b)   Magnesium

Magnesium is an important cofactor which is needed by the body for the conversion of vitamin D into its active form, calcitriol. Without magnesium alongside Vitamin D3 you may not convert vitamin D into calcitriol, the form of the vitamin that regulates calcium absorption, bone health, and the immune function.

Our diets are often deficient in magnesium, but you can address this by eating eating plenty of seeds, e.g chia, flax, pumpkin, hemp, flax which are great sources of magnesium, almonds, cashews and dark chocolate. Consider a supplement if you think you could be deficient.

2.   Vitamin C and zinc

In addition to Vitamin D, there are many other vitamins and minerals that are important for immune health. However, Vitamin C and Zinc are particularly important.

Vitamin C and immune health

Vitamin C plays multiple roles in immune defence. It boosts white blood cells so they can fight infections more effectively. It is also a powerful antioxidant that protects immune cells from damage during infections. Vitamin C also supports antibody production, helping the body target viruses and bacteria and strengthens barriers like skin and blood vessels through collagen production.

Practical steps for Vitamin C

• Eat citrus fruits, berries, peppers, kiwi, broccoli/leafy greens daily

• RNI - the recommended daily intake for this vitamin  is 65–90 mg/day, but for immune support, 500–1000 mg/day is commonly used

• Divide doses throughout the day for better absorption

• During acute illness, short-term use of 1–3 grams/day may help — but watch for side effects like diarrhoea

Zinc and immune health

Zinc is essential for the development and activation of T-cells — the white blood cells that coordinate immune responses. It also helps maintain skin and mucous barriers, regulates inflammation and prevents it from becoming excessive and provides antioxidant defence alongside Vitamin C.

Practical steps for Zinc

• Food sources: beef, lamb, shellfish, pumpkin, sesame, hemp and poppy seeds, soy-beans, peanuts, beans

• RNI – the recommended intake for this mineral is: 11 mg/day for men, 8 mg/day for women

• Dose - for immune support, 15–20 mg/day is often used short-term (always under guidance)

• Type of zinc - zinc glycinate and zinc gluconate are good choices as they are more easily absorbed than other types

Warning: be cautious as too much zinc (>40 mg/day long-term) can lower immunity and deplete copper.

Summary of Recommendations

• Expose skin to sunlight in summer, being careful not to burn

• Test your vitamin D blood levels in early autumn

• Take an oil based vitamin D3 supplement daily in the winter months; higher doses only if deficiency is confirmed and under medical supervision

• Take vitamin D year-round if you are unable to spend much time outdoors in summer

• Aim for serum levels of vitamin D above 75 nmol/L for optimal immune support.

• Consider a combined D3 + K2 supplement for best results, and ensure you have enough magnesium

• Ensure sufficient vitamin C and zinc are taken from foods or through supplementation

References

• Komaroff, A.L. (2017). Inflammation correlates with symptoms in chronic fatigue syndrome. PNAS. https://doi.org/10.1073/pnas.1712475114

• Davis, H.E. (2023). Long COVID: major findings, mechanisms and recommendations. Nature Reviews. https://www.nature.com/articles/s41579-022-00846-2

• Nielsen, N.M. et al. (2022). Vitamin D status and severity of COVID-19. Nature.

• Matsuda, Y. et al. (2025). Clinical Characteristics of Vitamin D Deficiency in Long COVID Patients. Nutrients, 17, 1692. https://doi.org/10.3390/nu17101692

• Di Filippo, L. et al. (2023). Low Vitamin D Levels Are Associated With Long COVID Syndrome. J Clin Endocrinol Metab, 108(10), e1106–e1116. https://doi.org/10.1210/clinem/dgad207

• Charoenporn, V. et al. (2024). High-dose vitamin D supplementation on fatigue and neuropsychiatric manifestations in post-COVID syndrome. Psychiatry Clin Neurosci, 78:595–604. https://doi.org/10.1111/pcn.13716

• Zabihiyeganeh, M. et al. (2023). Serum vitamin D status and pro-inflammatory cytokines in fibromyalgia patients. Clin Nutr ESPEN, 55:71–75. https://doi.org/10.1016/j.clnesp.2023.03.006

• Saija, C. et al. (2025). Role of Vitamin D Status and Alterations in Gut Microbiota Metabolism in Fibromyalgia Pain. Biomedicines, 13, 139. https://doi.org/10.3390/biomedicines13010139