From October, the NHS says everyone should “consider” a vitamin D supplement. The reason is sunlight — from about late March or early April to the end of September most people make all they need from the sun, but from October to early March sunlight is not enough. The daily amount from age 1 is 10 micrograms (400 IU), and the adult upper limit is 100 micrograms (4,000 IU) a day. This sets out the NHS page “Vitamin D”.
1. October to early March: consider 10 micrograms a day. Pregnant and breastfeeding women included.
2. 1 microgram = 40 IU. So 10 micrograms is 400 IU.
3. Adult upper limit: 100 micrograms (4,000 IU) a day. 50 micrograms for ages 1 to 10, 25 micrograms under 1.
Why from October — the sunlight season
The NHS says that from about late March or early April to the end of September, most people can make all the vitamin D they need from sunlight on their skin. From October to early March, sunlight is not enough. So in that period everyone should consider a daily 10 microgram supplement; taking one in spring and summer is optional.
These months are for the UK. The page does not say whether the same months apply at Korea’s latitude (our reading).
How much — daily amount and upper limit
| Who | Daily amount | Daily upper limit |
|---|---|---|
| Adults (incl. pregnant, breastfeeding, older) | 10 micrograms (400 IU) | 100 micrograms (4,000 IU) |
| Ages 11 to 17 | 10 micrograms | 100 micrograms (4,000 IU) |
| Ages 1 to 10 | 10 micrograms | 50 micrograms (2,000 IU) |
| Under 1 | 8.5 to 10 micrograms | 25 micrograms (1,000 IU) |
The NHS gives 1 microgram as 40 IU, and says people with some medical conditions may need less and should follow their doctor’s advice. US National Institutes of Health figures (such as 600 IU) are in women’s bone health — the numbers differ between agencies.
Who should take it all year
| Who | What the NHS says | Amount |
|---|---|---|
| People rarely outdoors | Frail or housebound, or living in a care home | 10 micrograms a day |
| People who cover most skin outdoors | Usually wear clothes covering most of the skin | 10 micrograms a day |
| People with dark skin | African, African-Caribbean or South Asian backgrounds — “consider” | 10 micrograms a day |
| Children 1 to 4 | All year | 10 micrograms a day |
| Babies under 1 | Breastfed, or formula-fed on less than 500ml a day | 8.5 to 10 micrograms a day |
The first three rows are what the NHS groups as “adults and children over 4”.
From food
The NHS lists oily fish such as salmon, sardines, trout, herring and mackerel, red meat, egg yolks, fortified foods such as some fat spreads and breakfast cereals, and liver — but liver should be avoided in pregnancy. UK cows’ milk is generally not a good source because it is not fortified.
Too much
Taking too much from supplements over a long time can cause hypercalcaemia, too much calcium in the body, which can weaken bones and damage the kidneys and heart. You cannot overdose from sunlight, but the page says to protect your skin during long periods in the sun.
Checklist
- ☐ October to early March — consider 10 micrograms (400 IU) a day
- ☐ Check label units — micrograms and IU (1 microgram = 40 IU)
- ☐ Adults: no more than 100 micrograms (4,000 IU) a day
- ☐ Lower limits for children — 50 micrograms at 1 to 10, 25 under 1
- ☐ Medical condition? Ask your doctor
Questions that remain
Should people in Korea start in October too?
This is the UK guidance; we did not read Korean agencies’ vitamin D standards, so we give no Korean figures.
What else for winter health?
Cold-related illness is covered in cold-related illness in winter.
Sources
- NHS — Vitamin D — original (page last reviewed 3 August 2020, next review due 3 August 2023 — still online past that date; checked 12 October 2026). 10 micrograms, 8.5 to 10 micrograms, 40 IU, late March to end of September and October to early March, year-round groups, 500ml, 100, 50 and 25 micrograms, hypercalcaemia.
- Not read. Korean agencies’ vitamin D intake standards.
- Added by us. The note that these are UK months.
Where to check further
- Supplement label — micrograms or IU per tablet.
Written 12 October 2026. The content follows the NHS original; the glosses are ours.