Do you need vitamin D in winter? Pick your month and see
Most of your vitamin D comes from summer sunshine on your skin, not from food, so whether you need extra depends on the month.
Pick a month, add how often you eat salmon, eggs, fortified cereal and other sources, and see your daily average from food next to the UK's 10 µg and EFSA's 15 µg reference points. Includes who is advised to take it all year, what the research says (mixed beyond bones) and the 100 µg upper limit.
Vitamin D helps your body absorb calcium, so it matters for bones, teeth and muscles. It is an odd vitamin, because most of what you get does not come from food at all. Your skin makes it when summer sunshine hits it. That is why the honest answer to "do I need it?" depends on the month, and this guide lets you check yours.
Why winter is different
From about late March or early April to the end of September, most people in the UK can make enough vitamin D from sunlight on their skin, according to the NHS. From October to early March the sun is too low and weak, so your skin makes very little. The NHS therefore advises a daily 10 microgram (µg) supplement in autumn and winter. Countries further south have a longer sunny season, so check your own national guidance.
Some people are advised to take 10 µg all year: those who are rarely outdoors, who usually cover most of their skin when outside, or who have dark skin (including African, African-Caribbean and South Asian backgrounds), because they make less from the same sunlight.
How much from food?
Food helps, but only a few foods carry much, and the UK's 10 µg is hard to reach with diet alone. Oily fish such as salmon and trout is the richest everyday source. Eggs, fortified breakfast cereals and fortified drinks add small amounts, and mushrooms contribute only if the pack says they were exposed to UV light. Fortification differs by country and brand, so read the label.
Try it: pick a month, then add how many times a week you eat each food. The bar shows your daily average against two reference points, and the result changes with the season.
What the numbers show
A week with two portions of salmon, a few eggs, some fortified cereal and a few glasses of fortified milk still averages under 10 µg a day once you divide by seven (about 6.6 in the example above), and without fish the food total is usually only a few micrograms. That gap is why the winter advice is a supplement rather than a food plan. In the sunny season, sunlight does most of the work, so food matters less.
Sunlight is the main source for most people from spring to autumn. In the low-sun months, food rarely closes the gap alone.
The two reference points differ for a reason. The NHS 10 µg is the amount advised across the UK. EFSA's 15 µg is an adequate intake for adults assuming minimal sun exposure, so it is a cautious figure for people who get none.
What the research says (it is mixed)
Vitamin D clearly matters for bones, and correcting a real shortfall is well established. Beyond that, the evidence is less tidy. The large US VITAL trial gave about 25,900 mostly healthy older adults 2,000 IU (50 µg) a day for up to six years and found no significant drop in heart attacks, strokes or cancer compared with placebo. So vitamin D is not a cure-all, and more is not better: the NHS and the US NIH both set an upper limit of 100 µg (4,000 IU) a day from all sources.
What to look for
If you are thinking about a supplement, three things matter at any budget. Check the amount on the label in micrograms (1 µg equals 40 IU) and stay at the reference amount unless a professional says otherwise. Check that the product is made for your age group, as children and babies have their own advice. And do not add a second product on top without checking the total, because the upper limit counts everything.
This is general information, not medical advice. If you have a condition (especially kidney disease, high calcium or a bone condition), are pregnant or breastfeeding, have or had an eating disorder, take medication, or have dark skin or cover most of your skin outdoors, talk to a doctor, pharmacist or dietitian about what is right for you before starting a supplement.
Sources
- NHS: Vitamin D (10 µg a day, October to early March, groups at risk, 100 µg upper limit)
- EFSA: Dietary reference values for vitamin D (adequate intake of 15 µg, assuming minimal skin synthesis)
- NIH Office of Dietary Supplements: Vitamin D (food values, 100 µg upper limit)
- Welsh Government: New advice on vitamin D intake (October to March, all-year groups)
- Science News: Vitamin D supplements don't prevent heart disease or cancer (VITAL trial summary)