Vitamin D helps the body absorb calcium and keep bones and muscles healthy. Most of it is made in the skin from sunlight, so deficiency is common in winter, in people who spend little time outdoors, and in people with darker skin living in countries far from the equator. Mild deficiency often has no symptoms; more severe deficiency can cause bone pain, muscle weakness and, in children, rickets.
Symptoms of low vitamin D
- Tiredness
- Bone pain, especially in the back, hips and legs
- Muscle aches and weakness
- Low mood (association, not proven cause)
- In children: rickets (bowed legs, delayed growth, soft skull)
- In adults: osteomalacia (soft bones)
Who is at higher risk?
- People with brown or black skin living in northern countries such as the UK, Ireland, Canada and Northern Europe
- People who cover most of their skin outdoors
- People who are housebound, in care homes, or work night shifts
- Older adults
- Pregnant and breastfeeding women
- Babies who are breastfed (in some countries supplements are advised)
- People with obesity, kidney or liver disease, or conditions affecting absorption
Food sources
- Oily fish: salmon, sardines, mackerel, herring
- Egg yolks
- Red meat and liver
- Fortified foods: some cereals, spreads, milks and plant milks
Food alone rarely provides enough in winter.
General supplement guidance
- In the UK, the NHS advises everyone to consider a daily supplement containing 10 micrograms (400 IU) of vitamin D in autumn and winter, and all year for people at higher risk
- Other countries have different recommendations; check your national guidance
- Higher treatment doses for proven deficiency should only be taken as prescribed after a blood test
Can you take too much?
Yes. Taking very high doses for long periods can raise calcium levels, causing nausea, thirst, kidney problems and heart rhythm problems. Don’t exceed recommended amounts unless a doctor advises.
For nurses on night shifts
Night workers may get very little daylight. Spending time outside on days off and following national supplement advice can help.
Frequently asked questions
Can I get enough vitamin D through a window?
Not usually. Most glass blocks the UVB rays needed to make vitamin D.
How do I know if I’m deficient?
A blood test (25-hydroxy vitamin D) can confirm it. Your doctor will decide whether testing is needed.
Related reading: Seasonal affective disorder · Anaemia and iron-rich foods
Checked against NHS guidance on vitamin D. Updated 5 November 2026.