The Number People Are Still Getting Wrong
Every autumn, the same thing happens. Someone comes into the shop, pulls out a pot of 400iu vitamin D from a supermarket bag, and asks if it will do the job. I look at it. I tell them it probably will not. And then I explain why the guidance has moved on and most of the retail market has not caught up with it.
I have been behind a counter selling supplements for thirty years. Vitamin D is the one nutrient where I have seen the conversation shift the most in that time. Not because of trends or marketing. Because the evidence base has consistently pointed toward higher doses than we were told for decades, and the experts have started to say so out loud.
This post is about what that shift means for you, what to buy, and what to skip.
Why the UK Is a Special Case
This is not a minor detail. The UK sits at a latitude where, from roughly October through to March, the sun is simply not strong enough to trigger meaningful vitamin D production in the skin. The angle of the sun is too low. You can spend time outside every single day during a British winter and still produce almost nothing.
That is not a deficiency myth. It is geography. And it applies to everyone in the country, regardless of diet or lifestyle.
The government has acknowledged this. The NHS recommends that everyone in the UK considers a vitamin D supplement through autumn and winter. The floor they suggest is 400iu. The problem is that 400iu is a very modest amount, and for many people it may not move the needle much at all.
How 4000iu Became the Dose Worth Knowing
When customers ask me what dose actually makes sense, I tell them what I have come to believe after thirty years: 4000iu is now the figure that informed practitioners and suppliers are working around.
It sits well within what is considered a safe daily intake for most adults. The European Food Safety Authority has reviewed the data and placed the tolerable upper intake level for adults at 4000iu per day. That is not a target, it is a ceiling. But the fact that 4000iu sits right at that ceiling matters. It is a dose that has been assessed and found appropriate for daily use in healthy adults.
The older 400iu figure was established to address the most severe end of deficiency. It was never really about supporting good everyday levels. There is a meaningful difference between not being critically low and having levels that are actually working for you.
D3 Specifically, Not Just D
If a label just says vitamin D without specifying the form, be cautious. There are two main forms:
- D2 (ergocalciferol) - plant-derived, but less effective at raising and maintaining levels in the body. Common in cheaper supplements and fortified foods.
- D3 (cholecalciferol) - the form your skin produces when exposed to sunlight. Better absorbed and more effective at contributing to healthy vitamin D status. This is the form worth buying.
Most reputable brands have moved to D3. Vegan D3 is also available, derived from lichen rather than lanolin, so plant-based customers no longer need to compromise.
I stock Viridian Vegan Vitamin D3 4000iu (from Lichen) Capsules. It is the product I point most customers toward when they want a clean, properly dosed D3 without animal-derived ingredients. Right form, right dose, brand I trust.
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Does D3 Work Better With Anything Else?
Yes, and this is where the conversation usually goes next. Vitamin D3 and vitamin K2 are often paired because they work in complementary ways. K2 contributes to normal bone health and plays a role in how calcium is directed around the body. If you are taking D3 consistently, adding K2 is worth considering.
I wrote a dedicated post on this combination if you want the full picture. For a standalone K2, Viridian Vitamin K2 Vegan 60 Capsules is what I keep in stock and use myself.
Comparing Common Vitamin D Options
| Product type | Typical dose | Form | Suitable for vegans | Worth buying? |
|---|---|---|---|---|
| Supermarket own-brand D | 400iu | Often D2 or unspecified | Sometimes | Marginal for winter use |
| Standard pharmacy D3 | 1000iu | D3 (lanolin) | No | Better, but still low |
| Higher-dose D3 (generic) | 2000-4000iu | D3 (lanolin) | No | Good dose, check excipients |
| Viridian Vegan D3 4000iu | 4000iu | D3 (lichen) | Yes | Yes, this is the one I stock |
Who Should Be Especially Consistent
Everyone in the UK benefits from supplementing D3 through autumn and winter. But some groups have more reason than most to be careful about consistency:
- People with darker skin tones - Higher melanin reduces how efficiently the skin synthesises vitamin D from sunlight, making supplementation more important year-round.
- Older adults - Skin becomes less efficient at producing vitamin D with age, and the body's ability to process it also changes.
- People who spend most of the day indoors - Office workers, shift workers, those with limited mobility. Low summer exposure makes the winter gap worse.
- Those on certain medications - Some drugs affect how the body handles fat-soluble vitamins. Talk to your GP before adding a higher-dose supplement if this applies to you.
- Anyone told their levels are low - If a blood test has flagged low vitamin D, discuss the right dose with your GP rather than guessing.
No supplement will treat or cure a deficiency. A GP conversation is the right starting point if you have real concerns about your levels.
What to Look For on the Label
Here is what to check before you put a vitamin D supplement in the basket:
- Form - D3 specifically. If it says D2 or ergocalciferol, put it back.
- Dose - 2000iu is a reasonable winter minimum. 4000iu if you want to work at the level the evidence supports.
- Excipients - Cheaper products often carry more fillers and binders. Worth checking.
- Vegan source - Lichen-derived D3 if that matters to you. Lanolin comes from sheep's wool.
Browse our full range of Vitamins and Minerals to see what we actually carry.
FAQ
Is 4000iu of vitamin D3 safe to take every day?
For most healthy adults, yes. The European Food Safety Authority places the tolerable upper intake level at 4000iu per day. If you are on medication, have a health condition or have been advised otherwise, talk to your GP first. Individual circumstances vary.
Can I get enough vitamin D from food alone?
It is very difficult, especially through a UK winter. Oily fish, egg yolks and some fortified foods contain vitamin D, but not in amounts that come close to what a supplement provides. Food should complement a supplement, not replace it.
When should I start taking vitamin D in autumn?
October is the sensible starting point, continuing through to April. People with limited sun exposure in summer may benefit from starting earlier. Consistency through the winter months matters more than the precise start date.
Should I take vitamin D with food?
Yes. It is fat-soluble, so it absorbs better alongside a meal containing some fat. Avoid taking it on an empty stomach.
Do I need a blood test first?
Not necessarily for a standard daily dose in the 400iu to 4000iu range if you are a healthy adult. But if you have symptoms that concern you or want to track your levels, a test is a sensible step. Your GP can arrange one.