top of page
Search

Vitamin D and Your Immune System: What You Need to KnowBy a Nutritionist in Bristol

  • Aug 6
  • 3 min read
Nutritionist in bristol

As a nutritionist in Bristol, people often ask: “Do I really need vitamin D?” The answer is usually yes—especially in the UK, where sunlight (our main source of vitamin D) is limited for much of the year. Vitamin D does much more than support your bones. It plays a crucial role in your immune system—from fighting infections to influencing cancer immunity. Here’s why it matters.


Vitamin D and Immune Function

Scientific studies show vitamin D plays vital roles:

  1. Controls inflammation by inhibiting dendritic-cell maturation and preventing excessive immune reactions (1).

  2. Enhances microbial defence: boosts antimicrobial peptides like cathelicidin; deficiency linked to increased infection risk, particularly in darker-skinned individuals (2).

  3. Promotes regulatory T cells, reducing inflammation through synergy with IL‑2 (3).

  4. Supports cancer immunity: vitamin D influences gut microbiome (increasing bacteria like Bacteroides fragilis) and improves responses to immunotherapy (5).

  5. Reduces pro-inflammatory T helper 1 programs, which may protect against chronic disease (4).


UK Daily Recommendations

According to the British Dietetic Association:

Adults and children aged 4+ years: 10 µg/day (~400 IU), year‑round for most people—or at least during autumn and winter for those with normal sun exposure (BDA, 2024a).

At-risk groups (dark skin, covering clothing, older age, housebound, obese, certain health conditions): 10 µg/day all year (BDA, 2024a; GOV.UK, 2021).

Infants (0–12 months): 8.5–10 µg/day (BDA, 2021).

Children aged 1–4 years: 10 µg/day (BDA, 2021).


Supplement Guidance

Adults (4+ years):

  • General population: 10 µg/day during October–March (6,7).

  • At-risk: 10 µg/day all year (6,7).

  • Do not exceed +100 µg/day (~4,000 IU) to avoid toxicity (8).


Getting Enough from Food & Sunlight

Sunshine: Safe exposure (arms/legs, 20–30 min, 3–4 times/week from April to September) provides most vitamin D for light-skinned individuals; less effective for darker skin or sunscreen users (6).

Food sources are limited but helpful:

Oily fish (salmon, sardines, mackerel), egg yolks, liver, red meat.

Fortified breakfast cereals, fat spreads, plant milks (6).

Food alone provides only ~20% of required vitamin D (6).



Final Thoughts FROM A Nutritionist in bristol

Vitamin D is essential not just for bone health but for immune balance, infection defence, and even cancer protection. With limited UK sunlight, supplements of 10 µg/day, at least during autumn and winter—or year-round for at-risk groups—are recommended.


A diet rich in oily fish, eggs, and fortified foods helps, but supplements are often needed.

If you experience winter fatigue, frequent illness, autoimmune concerns, or have darker skin or limited outdoor exposure, consider testing your vitamin  D levels or speak to a nutritionist in Bristol for tailored advice. Get in touch today to book a free 15 minute discovery call.

 

Disclaimer

The information on this blog is here to help and inspire, but it’s not meant to replace professional advice. Always check with a doctor before making any changes to your diet or lifestyle. The views shared are those of the author(s) and may not reflect those of any organisations involved. Rosy Nutrition & Personal Training can’t be held responsible for any outcomes from using this information.


References

  1. Hewison, M. et al. (2003) Differential regulation of vitamin D receptor and its ligand in human monocyte-derived dendritic cells, [online]. Available at: https://pubmed.ncbi.nlm.nih.gov/12759412/ (Accessed 16th July 2025)

  2. Liu, P.T. et al. (2006) Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response, [online]. Available at: https://pubmed.ncbi.nlm.nih.gov/16497887/A (Accessed 16th July 2025)

  3. Jeffery, L.E. et al. (2009) 1,25-Dihydroxyvitamin D3 and IL-2 combine to inhibit T cell production of inflammatory cytokines and promote development of regulatory T cells expressing CTLA‑4 and FoxP3, [online]. Available at: https://pubmed.ncbi.nlm.nih.gov/19843932/ (Accessed 16th July 2025)

  4. Chauss, D. et al. (2022) Autocrine vitamin D signaling switches off pro-inflammatory programs of TH1 cells, [online]. Available at: https://pubmed.ncbi.nlm.nih.gov/34764490/ (Accessed on 16th July 2025)

  5. Giampazolias, E. et al. (2024) Vitamin D regulates microbiome-dependent cancer immunity, [online]. Available at: https://pubmed.ncbi.nlm.nih.gov/38662827/ (Accessed on 16th July 2025)

  6. British Dietetic Association (BDA) (2024a) Vitamin D, [online]. Available at: https://www.bda.uk.com/resource/vitamin-d.html (Accessed 16 July 2025).

  7. GOV.UK (2021) Vitamin D and clinically extremely vulnerable (CEV) guidance, available at: https://www.gov.uk/government/publications/vitamin-d-for-vulnerable-groups/vitamin-d-and-clinically-extremely-vulnerable-cev-guidance (Accessed 16 July 2025).

  8. NHS (n.d.) Vitamin D. In: Vitamins and minerals [online]. Available at: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin‑d/ (Accessed: 6 August 2025).

Comments

bottom of page