Vitamin D: Why It Matters and How to Avoid Deficiency

Vitamin D is a fat-soluble vitamin that also functions as a hormone, produced in the skin when exposed to UVB rays from sunlight. Once produced, it plays a role in multiple systems throughout the body.

Vitamin D is essential for keeping bones, teeth, and muscles healthy because it helps regulate calcium and phosphate levels. Deficiency is well known to be linked to bone pain, muscle weakness, osteoporosis in adults, and rickets in children (soft or weak bones) (Liu et al., 2025). However, deficiency does not always present with obvious symptoms. Other signs and symptoms of vitamin D deficiency can include fatigue or low energy, low mood or depressive symptoms, and persistent pain (El Miedany, 2025).

Vitamin D also plays a role in immune function and has been associated with depression, cancer risk, and an increased risk of cardiovascular events (Ellison & Moran, 2021; Saji Parel et al., 2022).

One large population-based study found a significant association between vitamin D deficiency and total cancer mortality. Individuals with bowel, prostate, stomach, and lung cancer were shown to have a higher risk of death if they were deficient in vitamin D (Sha et al., 2023).

During the summer months, most people obtain sufficient vitamin D through sunlight exposure. However, this is not possible during autumn and winter in the UK, as UV levels are not strong enough for vitamin D synthesis.

Certain groups are at higher risk of vitamin D deficiency, including:

• Older adults

• Ethnic minority groups (particularly South Asian and African-Caribbean communities, due to higher melanin reducing vitamin D synthesis)

• People who spend little time outdoors or are housebound

• Individuals with medical conditions affecting nutrient absorption, such as coeliac disease, cystic fibrosis, gastric bypass surgery, short bowel syndrome, and inflammatory bowel disease (Omeed Sizar et al., 2023).

Are you getting enough vitamin D?

Vitamin D is found naturally in only a small number of foods, such as oily fish (e.g., salmon, mackerel, sardines), egg yolks, liver, and red meat. Because dietary sources are limited, most people are unable to meet their vitamin D requirements through food alone during autumn and winter.

For this reason, the UK Department of Health recommends that:

• Adults and children over 4 years take a daily supplement of 10 micrograms (10 μg) of vitamin D between October and early March.

• Children aged 1 to 4 years should take a daily supplement containing 10 micrograms (10 μg) of vitamin D throughout the year.

• For babies: From birth, breastfed infants are recommended to be given a daily vitamin D supplement of 8.5–10 micrograms (μg), since breastmilk alone does not provide sufficient vitamin D for bone development and overall health. Formula‑fed babies do not usually need a supplement if they are having 500 ml or more of first infant formula per day, because infant formula is fortified with vitamin D. Health visitors and other health professionals in the UK routinely advise parents about these recommendations and where to access suitable infant vitamin drops (NHS, 2025).

  
  

Despite public health recommendations, vitamin D deficiency remains common in the UK. According to the National Diet and Nutrition Survey (2019–2023), low vitamin D status was observed in:

• 10% of children aged 4 to 10 years

• 23% of children aged 11 to 18 years

• 18% of adults aged 19 to 64 years

  
  

This highlights that despite guidance on supplementation and sun exposure, significant portions of the population still have insufficient vitamin D levels (National Diet and Nutrition Survey, 2019–2023).

Top tips for ensuring you and your family are getting enough vitamin D

• Supplement daily during autumn and winter (as above). Those with darker skin, limited sun exposure, or who are housebound may benefit from taking a supplement year-round. Supplements may be labelled in international units (IU); 10 μg is equivalent to 400 IU (NHS, 2020).

  
  

  To improve absorption, it’s best to take vitamin D supplements with a meal that contains some healthy fat, such as avocado, nuts, seeds, olive oil, or dairy products, as vitamin D is fat-soluble and is better absorbed alongside dietary fats.

  
  

• Include vitamin D–rich foods where possible. Oily fish and eggs are good sources, while everyone can benefit from fortified foods such as breakfast cereals, spreads, and plant-based dairy alternatives with added vitamin D.

  
  

• Choose vitamin D–enriched mushrooms. Certain mushrooms grown under UV light may have enhanced vitamin D levels and can be a helpful additional source. These will be clearly labelled in supermarkets and can help contribute to overall intake.

  

  
  

• Speak to a healthcare professional if you are concerned. If you have concerns about your vitamin D intake or are experiencing symptoms that feel out of the ordinary, it may be helpful to seek further guidance from your doctor (GP). You may find it useful to read 🌱 Listening to Your Body: When to Ask for a Free NHS Health Check, which explains when a free NHS health check may be appropriate.

  
  

Vitamin D deficiency is common in the UK, especially during autumn and winter months, but often goes unnoticed. Understanding its role in health and knowing who may be at risk allows for informed, preventative steps to be taken. For many people, a simple daily supplement during the darker months can play an important role in supporting long-term health and wellbeing.

References:

Agostini, D. and Donati Zeppa, S. (2023) ‘Vitamin D, diet and musculoskeletal health’, Nutrients, 15(13), p. 2902. doi: 10.3390/nu15132902. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC10346490/ (Accessed: 29 January 2026).

El Miedany, Y. (2025) ‘Evidence‑based guidelines for vitamin D optimisation’, Journal of Clinical Nutrition and Metabolism, 15(3), pp. 45–58. doi: 10.1186/s43166‑025‑00330‑8. Available at: https://link.springer.com/article/10.1186/s43166‑025‑00330‑8 (Accessed: 29 January 2026).

Ellison, J. and Moran, D. (2021) ‘Vitamin D and bone health’, Journal of Clinical Nutrition, 75(4), pp. 312–318.

Liu, Y., Wang, W., Yang, Y., Deng, J. and Zhang, Z. (2025) ‘Vitamin D and bone health: from physiological function to disease association’, Nutrition & Metabolism, 22, p. 113. doi: 10.1186/s12986‑025‑01011‑1. Available at: https://nutritionandmetabolism.biomedcentral.com/articles/10.1186/s12986‑025‑01011‑1 (Accessed: 29 January 2026).

National Diet and Nutrition Survey (2025) National Diet and Nutrition Survey 2019 to 2023: Report. London: Public Health England. Available at: https://www.gov.uk/government/statistics/national-diet-and-nutrition-survey-ndns-results-from-years-11-to-14-2019-to-2023 (Accessed: 29 January 2026).

NHS (2020) Vitamin D: Why it’s important and how to get enough. Available at: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/ (Accessed: 29 January 2026).

NHS (2025) Vitamins for babies — Best Start in Life. Available at: https://www.nhs.uk/best-start-in-life/baby/baby-basics/caring-for-your-baby/vitamins-for-babies/ (Accessed: 29 January 2026).

Omeed Sizar, Swapnil Khare, Amandeep Goyal and Amy Givler (2023) ‘Vitamin D deficiency: causes and consequences’, Nutrition Reviews, 81(2), pp. 150–165.

Saji Parel, T., et al. (2022) ‘Vitamin D status and cardiovascular risk: a meta‑analysis’, Cardiovascular Research, 118(1), pp. 85–95.

Sha, S., Chen, L.‑J., Brenner, H. and Schöttker, B. (2023) ‘Associations of 25‑hydroxyvitamin D status and vitamin D supplementation use with mortality due to 18 frequent cancer types in the UK Biobank cohort’, European Journal of Cancer, 191, p. 113241. doi: 10.1016/j.ejca.2023.113241. Available at: https://pubmed.ncbi.nlm.nih.gov/37549530/ (Accessed: 29 January 2026).