Vitamin D is important for bone and muscle health. It may also have a role in the body's immune response to respiratory viruses. Sunlight exposure is the main source of vitamin D for most people in the UK during summer months. But, between October and early March, people in the UK do not make enough vitamin D from sunlight. Vitamin D is also found in a small number of foods and can be obtained from supplements. The 2 key forms of vitamin D, D3 (colecalciferol) and D2 (ergocalciferol), are licensed for preventing and treating vitamin D deficiency. They are not specifically licensed for preventing or treating any infection, including SARS‑CoV‑2 that causes COVID‑19.

Vitamin D status is determined by measuring serum concentrations of 25 hydroxyvitamin D (25[OH]D), the major circulating metabolite of vitamin D. Existing UK government recommendations on vitamin D are based on advice from the Scientific Advisory Committee on Nutrition (SACN). To protect bone and muscle health, the SACN vitamin D and health report recommends that serum 25(OH)D concentration should not fall below 25 nmol/litre at any time of the year. To achieve this, SACN recommends a reference nutrient intake of 10 micrograms (400 units; also called international units [IU]) of vitamin D daily for the UK population aged 4 years and above. This is the average amount needed by 97.5% of the population to maintain a serum concentration of 25 nmol/litre when UVB sunshine exposure is minimal. UK government advice on taking a vitamin D supplement includes:

  • 10 micrograms (400 units) of vitamin D daily for everyone in the UK aged over 4 years between October and early March, and

  • 10 micrograms (400 units) of vitamin D daily throughout the year for people whose serum 25(OH)D concentrations may not reach 25 nmol/litre through sunlight alone.

The dose of vitamin D in units can be calculated by multiplying the number of micrograms by 40; for example, 10 micrograms is equivalent to 400 units. This guideline uses 'units' instead of 'international units' or 'IU' for doses of vitamin D. This is consistent with the BNF guidance on prescription writing, and stems from the preferred convention of using 'units' because of safety concerns about using 'IU' in prescribing.

There are services supplying free vitamin D supplements to some population groups. For example, there is an NHS service supplying free daily vitamin D supplements for people at high risk (clinically extremely vulnerable) from COVID‑19. This service has been set up because it is particularly important for people who have been indoors more over the spring and summer while shielding to take vitamin D for bone and muscle health. Women and children who qualify for the Healthy Start scheme can also get free supplements containing vitamin D.

ISBN: 978-1-4731-3942-8