Vitamin D is essential for healthy bones. We get some of it from food, but most comes from sunlight.
Most people should be able to get all the vitamin D they need from summer sun and a healthy balanced diet. However, up to a quarter of the population has low levels of vitamin D in their blood.
Not getting enough sunlight is one reason some people suffer from vitamin D deficiency , putting them at risk of bone problems, including rickets in children and osteomalacia in adults. Some research suggests that not getting enough vitamin D may also be linked to heart conditions, diabetes , asthma and cognitive impairment in older adults.
Vitamin D is also found in oily fish, such as salmon, mackerel and sardines, eggs, fortified fat spreads, fortified breakfast cereals and powdered milk. However, it is hard to get enough vitamin D just from food.
Vitamin D deficiency at-risk groups
The Chief Medical Officers of the UK say these groups are at particular risk of vitamin D deficiency:
- Pregnant and breastfeeding women, especially teenagers and young women.
- Infants and children under 5 years of age.
- 65 year olds and over.
- People who have little or no exposure to the sun. This includes covering-up for cultural reasons, people who are housebound or who stay indoors for long periods of time.
- People with darker skin , such as African, African-Caribbean and South Asian origin. These groups are not able to make as much vitamin D as those with paler skin.
Blood test for vitamin D deficiency
The most accurate way to measure how much vitamin D is in your body is the 25-hydroxy vitamin D test. In the kidney , 25-hydroxy vitamin D changes into an active form of the vitamin. The active form of the vitamin can be measured through a blood test. The active form of vitamin D helps control calcium and phosphate levels in the body. The normal range is 80 to 120 nanomols per litre (nmol/L).
Safe sun exposure
Around 10 to 15 minutes a day in the summer sun without sunscreen is enough to top up vitamin D levels for most people. Health officials don't give firm recommendations on the duration because the ideal amount of sun depends on people's skin type and how quickly they get sun burn. People with darker skin need longer in the sun that those with lighter skin.
The best time of day for making vitamin D from sunlight is 11am to 3pm, April to October.
It doesn’t require putting on a bikini or trunks, but the bigger the area of the body uncovered, the more vitamin D the body makes.
After the daily vitamin D top-up, the usual sun protection measures should be taken, including using sun protection factor or at least SPF 15.
Vitamin D supplements
UK Health Departments recommend vitamin D supplements for the following at-risk groups:
- Pregnant and breastfeeding women - a daily supplement containing 10µg vitamin D
- Infants and young children 6 months to 5 years old - daily supplement drops containing 7-8.5 micrograms of vitamin D. If the mum hasn't had vitamin D supplements throughout pregnancy, breast fed babies may need drops from one month. Formula feed is already fortified with vitamin D. Talk to a GP or health visitor for specific advice. Free vitamins may be available under the Healthy Start Scheme.
- People aged 65 years and over - 10 micrograms of vitamin D a day.
- People who get little or no sun exposure - 10 micrograms of vitamin D a day.
Too much vitamin D?
You can't get too much vitamin D from being in the sun or food, but it is possible to take too much in the form of supplements.
Taking more than 25 micrograms of vitamin D a day could be harmful. Supplements may be marked in International Units, or IU, rather than micrograms. The conversion is 40 IU to one microgram. Seek medical advice if you have concerns.