Vitamin D in a UK Winter: NHS Advice and What Your Level Means

The NHS says everyone should consider taking a daily 10 microgram (400 IU) vitamin D supplement in autumn and winter, because from October to early March the sun in the UK is too weak for the skin to make enough.¹ The national diet survey shows the pattern in blood samples: 31% of adults aged 19 to 64 whose blood was taken between January and March had a level below 25 nmol/L, against 6% in July to September (2016 to 2023 combined).²

Below are the NHS advice, the survey figures by season and age, what the level bands mean, and what UK sources say about blood tests. This is general information, not advice on your own level: a GP or pharmacist can advise on what suits you.

What the NHS advises and who needs vitamin D all year

The NHS says everyone should consider a daily supplement containing 10 micrograms of vitamin D during autumn and winter, and some people should take one all year.¹ From about late March or early April to the end of September, it says most people can make the vitamin D they need from sunlight and a balanced diet, and may choose not to take a supplement in those months.¹

The NHS advises a supplement all year for people who are not often outdoors (for example frail or housebound people), who live in a care home or who usually cover most of their skin outdoors.¹ It says people with dark skin, for example with an African, African-Caribbean or south Asian background, should consider one all year.¹ Women and children who qualify for the Healthy Start scheme can get free supplements containing vitamin D.¹

The 10 microgram figure comes from the Scientific Advisory Committee on Nutrition (SACN), whose 2016 reference nutrient intake is the average daily amount needed by 97.5% of people to stay at or above 25 nmol/L when sunshine exposure is minimal.⁵ SACN's figure applies all year and counts food as well as supplements.⁵ Government advice to supplement in autumn and winter, rather than all year, reflects its view that in spring and summer most people get enough from sunlight and a balanced diet.⁶

How common low vitamin D is in the UK, by season

In the national diet survey, 31% of adults aged 19 to 64 had a vitamin D level below 25 nmol/L when their blood was taken in January to March, against 6% in July to September.² The share below 25 nmol/L by the three-month period in which blood was taken, pooling 2016 to 2023, is shown below.²

January to March: 31% of adults aged 19 to 64 (316 people) and 23% of those aged 65 and over (121 people)
April to June: 17% (342 people) and 14% (118 people)
July to September: 6% (269 people) and 1% (77 people)
October to December: 14% (342 people) and 9% (140 people)

Average levels were lowest in January to March in every age group, and across age and sex groups aged 11 and over the share below 25 nmol/L that quarter ranged from 21% to 38%, falling to between 0% and 10% in July to September.³ Across the whole year of sampling, 18% of adults aged 19 to 64 and 12% of those aged 65 and over were below 25 nmol/L in 2019 to 2023.³ Earlier rounds of the survey found 16% and 13% for the same two age groups in 2016 to 2019.⁹ The survey changed how blood samples were transported and processed from 2021, and its report does not compare the two periods, so 16% and 18% are two separate snapshots, not a trend.³

These figures describe blood levels, not illness. People were sampled in private households across the UK, so care-home residents are not represented, and 40% of the adults who completed the first interview gave a blood sample.³ The seasonal table pools survey years on both sides of that 2021 change, reports calendar quarters rather than October to March against April to September, and gives only the share below 25 nmol/L, not below 50.² The July to September figure for adults aged 65 and over rests on 77 people, so the 1% is approximate.²

Supplement use in the same survey was 28% of adults aged 19 to 64 and 35% of those aged 65 to 74 over its four recording days in 2019 to 2023, a count that includes multivitamins and covers the whole year, not October to March only.⁴

What a vitamin D level means: 25, 30 and 50 nmol/L

UK guidance uses 25 nmol/L as the level below which the risk of poor bone and muscle health rises, and says it is a risk threshold, not a diagnosis.⁵ SACN found the risk increased below about 20 to 30 nmol/L and kept 25 because no exact point within that range could be identified.⁵

SACN's report also sets out two higher lines from 2011 US guidance. The Institute of Medicine counted below 30 nmol/L as at risk of deficiency and 50 nmol/L and above as sufficient for practically everyone, and the Endocrine Society said people should be identified as deficient below 50 nmol/L.⁵ The same result can therefore count as low under one definition and adequate under another.

When a vitamin D blood test is used

The Royal Osteoporosis Society says you do not normally need a blood test to check whether you are getting enough vitamin D.⁸ It adds that a vitamin D test is often done before starting some osteoporosis medicines.⁸

The NHS page on rickets and osteomalacia says that if a GP thinks you may have osteomalacia (rickets in children), they check your vitamin D and calcium levels, which may include blood tests.⁷ Symptoms in adults include pain in the back, shoulder, ribs, pelvis or legs, and weak muscles that make climbing stairs or getting out of a chair difficult, and the NHS says to see a GP if you think you might have it.⁷ For advice on whether a test is right for you, speak to your GP.

If you want your own level measured

Vitamin D is included in three of the blood test profiles at our Mayfair clinic: the Vitamin Profile, the Well Woman Profile and the Well Man Profile. Our blood testing service includes a complimentary nurse consultation, and results are delivered within 24 to 48 hours.

We also offer a vitamin D injection at our Mayfair clinic. Before it, a registered nurse goes through your medical history, any medication or supplements you take, and any recent vitamin D blood test result, and confirms the injection is suitable for you.

Common questions

Can I get enough vitamin D from food?

Not easily: the NHS says it is difficult to get enough vitamin D from food alone.¹ Sources include oily fish, red meat, egg yolks and fortified foods such as some fat spreads and breakfast cereals, and UK cows' milk is generally not a good source because it is not fortified.¹ In the national diet survey, adults aged 19 to 64 averaged 2.6 micrograms a day from food in 2019 to 2023, about a quarter of the 10 micrograms SACN recommends.⁴

Can you take too much vitamin D?

Yes: the NHS says adults and children aged 11 to 17 should not take more than 100 micrograms (4,000 IU) of vitamin D a day as it could be harmful, and that 10 micrograms a day is enough for most people who choose to take a supplement.¹ Taking too much over a long period can cause calcium to build up in the body (hypercalcaemia), which can weaken the bones and damage the kidneys and the heart.¹ Younger children have lower limits, and some medical conditions mean a person cannot safely take as much, so the NHS says to consult a doctor if in doubt and to follow a doctor's advice if given a different amount.¹

Does the sun give you vitamin D in a UK winter?

No: the NHS says that between October and early March the body does not make enough vitamin D from sunlight in the UK.¹ The skin makes vitamin D from the ultraviolet B radiation in sunlight, and in the UK winter that radiation is too limited for the skin to make biologically relevant amounts.³ The NHS adds that you cannot overdose on vitamin D through sunlight, but should still cover up or protect your skin if you are out in the sun for long periods.¹