Vitamin D in Winter: How Much Do You Actually Need?
How much vitamin D to take from October to March, who needs it all year, D3 vs D2, and when more becomes too much, from NHS and NIH guidance.
6 min read
Most adults need a modest amount of vitamin D in winter, not a megadose. The NHS advises everyone to consider 10 micrograms (400 IU) a day from October to March, and the US recommendation is 15 micrograms (600 IU) a day for adults up to 70 and 20 micrograms (800 IU) over 70. Adults shouldn't go above 100 micrograms (4,000 IU) a day unless a doctor advises it.
Winter is when vitamin D levels tend to dip, because your skin makes less of it when the sun is low. Below is what official guidance says about how much to take, who needs it all year, which form to buy and when more becomes too much.
Why do you need more vitamin D in winter?
Because the sun in winter is too weak for your skin to make enough. The NHS says that between October and early March people in the UK don't make enough vitamin D from sunlight, while from about late March or early April to the end of September most people can make what they need from being outdoors[1].
Skin makes vitamin D from the sun's UVB rays. The NIH lists season, time of day, length of day, cloud cover, smog, skin melanin and sunscreen as factors that affect how much you make. Sunshine through a window doesn't count, because UVB doesn't pass through glass[2]. Food helps a little: oily fish, egg yolks, red meat and fortified foods such as some cereals and fat spreads contain vitamin D[1], but it is hard to get enough from unfortified food alone[2].
How much vitamin D should adults take in winter?
10 to 20 micrograms (400 to 800 IU) a day covers the official recommendations for most adults. The exact number depends on which guidance you follow. One microgram equals 40 IU[1].
| Who | UK (NHS) | US (NIH) | Upper limit |
|---|---|---|---|
| Adults 19–70 | Consider 10 mcg (400 IU) a day in autumn and winter[1] | 15 mcg (600 IU)[2] | 100 mcg (4,000 IU)[1][2] |
| Adults over 70 | 10 mcg (400 IU)[1] | 20 mcg (800 IU)[2] | 100 mcg (4,000 IU)[2] |
| Pregnancy and breastfeeding | 10 mcg (400 IU)[1] | 15 mcg (600 IU)[2] | 100 mcg (4,000 IU)[1][2] |
| Children 1–10 | 10 mcg (400 IU); all year for ages 1–4[1] | 15 mcg (600 IU)[2] | 50 mcg (2,000 IU) in NHS advice[1] |
| Babies under 1 | 8.5–10 mcg a day[1] | 10 mcg (400 IU)[2] | 25 mcg (1,000 IU)[1] |
The US amounts assume you get very little sun[2], which is why they're a little higher than the UK's winter figure. Both are far below the strength of many high-dose products on sale. More is not automatically better, so follow the label and ask your doctor before taking a high-strength product. Our vitamin D guide covers food sources and forms in more detail.
Who should take vitamin D all year round?
People who get little sun on their skin, even in summer. The NHS advises a daily supplement all year for people who are rarely outdoors, such as those who are frail or housebound, people who usually cover most of their skin outdoors, and children aged 1 to 4. People with dark skin may also not make enough from sunlight[1].
The NIH adds older adults, whose skin makes less vitamin D with age, breastfed infants, people with conditions that limit fat absorption, and people with obesity or who have had gastric bypass surgery[2].
Is vitamin D3 better than D2?
Both work, but D3 usually raises blood levels more and keeps them up longer. The NIH says both forms are well absorbed, but most evidence indicates that vitamin D3 increases blood levels of 25-hydroxyvitamin D to a greater extent and for longer than D2[2].
D3 is usually made from lanolin in sheep's wool, while D2 is made from yeast. If you avoid animal products, look for D3 from lichen, which is also available[2].
Can you take too much vitamin D?
Yes, from supplements, though not from the sun. The NHS says you can't overdose on vitamin D through sunlight[1], but taking too much from supplements over a long time can cause calcium to build up in the blood (hypercalcaemia), which can weaken bones and damage the kidneys and heart[1].
The NIH notes that vitamin D toxicity is almost always caused by supplements. US experts set the adult upper limit at 100 micrograms (4,000 IU) a day and noted that even intakes below that limit might have adverse effects over time, and they advised avoiding blood levels above about 125 to 150 nmol/L (50 to 60 ng/mL)[2]. Some people have medical conditions that mean they can't safely take as much; if a doctor has recommended a different amount, follow their advice[1].
Taking vitamin D with calcium supplements may raise the risk of some side effects[2]. If you take both, see can I take vitamin D and calcium together.
Should you get your vitamin D level tested before winter?
Not routinely, if you're healthy. MedlinePlus says routine vitamin D testing isn't recommended for everyone; it's usually done when a doctor suspects low vitamin D is behind a bone or other health problem, or for people at high risk[3]. The Endocrine Society also doesn't recommend routine testing in healthy people[2].
If you are tested, the result is usually given as 25(OH)D. US experts say 50 nmol/L (20 ng/mL) or more is enough for most people, and the risk of deficiency rises below 30 nmol/L (12 ng/mL)[2]. Ask your doctor to explain your number rather than self-treating with a high dose.
When should you take vitamin D, and what does it interact with?
Take it with a meal that contains some fat. The NIH says fat in the gut helps vitamin D absorption, although some is absorbed without it[2]. Time of day matters less than taking it consistently; our post on the best time to take supplements has more on timing.
Vitamin D can interact with orlistat, statins, steroids such as prednisone and thiazide diuretics[2]. If you take any of these, or have kidney disease, a calcium disorder or another long-term condition, check with your doctor or pharmacist before starting.
How Suppin helps
- The Nutrients tab adds up vitamin D from every product you take, including multivitamins, and shows it against the daily value and the upper limit.
- Reminders at the times you choose, so a winter vitamin D habit actually sticks, plus a heads-up before you run out.
- Your routine is built by fixed safety rules from your health answers, including pregnancy, medications and conditions, and anything that may interact shows "Review with a professional".
- Scan a barcode or photograph a label to check how many micrograms a product really contains.
Get Suppin on the App Store and set a daily reminder for the winter months.
FAQ
For most adults, no. 1,000 IU is 25 micrograms, which is above the NHS 10 microgram advice[1] but well below the adult upper limit of 100 micrograms (4,000 IU)[2]. Check what your other products already contain.
The NHS says most people can make enough vitamin D from sunlight between late March or early April and the end of September[1]. People who are rarely outdoors, cover their skin or are in another high-risk group should take it all year[1].
The NIH fact sheet doesn't list an interaction with magnesium. See magnesium and vitamin D and vitamin D and vitamin K2; if you take warfarin, ask your doctor before any vitamin K product.
No. UVB rays don't pass through glass, so sunshine indoors through a window doesn't make vitamin D[2].
The NHS advises 10 micrograms a day for children over 1 in autumn and winter, all year for ages 1 to 4, and no more than 50 micrograms a day for ages 1 to 10[1]. Babies have separate guidance, so ask your health visitor or pharmacist.
Sources
- NHS — Vitamin D
- NIH Office of Dietary Supplements — Vitamin D fact sheet
- MedlinePlus — Vitamin D test
Educational information, not medical advice. Check with your doctor or pharmacist before starting or changing supplements, especially if you take medication, are pregnant or have a health condition.
