Thirty Years of Watching People Take Too Little
I have been selling supplements from this shop in Paignton for thirty years. One pattern repeats itself more than any other. Someone comes in, tired, sluggish, not sleeping well. They mention they already take vitamin D. I ask how much. They say 400 IU. And there it is.
- I have been selling supplements from this shop in Paignton for thirty years.
- Your skin makes vitamin D when exposed to UVB sunlight.
- Vitamin D is a fat-soluble vitamin that behaves more like a hormone than a typical nutrient.
- Thirty Years of Watching People Take Too Little
- Why the UK Is a Particularly Bad Place for Vitamin D
- What Vitamin D Actually Does in the Body
- Why 400 IU Is a Floor, Not a Target
- Test, Do Not Guess
- Why You Should Pair Vitamin D3 With K2
- Choosing the Right Vitamin D Supplement in the UK
- FAQ
- From the shop
The NHS recommends 400 IU of vitamin D for adults during autumn and winter. That figure is not wrong, exactly. It is aimed at avoiding acute deficiency, not at supporting anything close to optimal blood levels. For most adults living in the UK, it is almost certainly not enough. Let me explain why, and what to do about it.
Why the UK Is a Particularly Bad Place for Vitamin D
Your skin makes vitamin D when exposed to UVB sunlight. That sounds fine until you remember where we live. The UK sits between roughly 50 and 60 degrees north latitude. From October through to March, the sun does not get high enough in the sky for meaningful UVB to reach your skin, even on a clear day. The angle is simply too low.
Even in summer, most adults spend the bulk of daylight hours indoors. Add cloud cover, sunscreen use, and longer working hours, and the window for natural vitamin D production is smaller than most people assume. By the time February arrives, a large proportion of UK adults are running on empty. This is geography and biology, and they do not care about your good intentions.
What Vitamin D Actually Does in the Body
Vitamin D is a fat-soluble vitamin that behaves more like a hormone than a typical nutrient. EFSA-authorised claims cover quite a lot of ground here, which tells you something about how fundamental this nutrient is.
- Bone maintenance - Vitamin D contributes to the maintenance of normal bones by supporting calcium absorption in the gut.
- Muscle function - It contributes to the maintenance of normal muscle function, which is why low levels often show up as general weakness or fatigue.
- Immune system support - Vitamin D contributes to the normal function of the immune system, a claim that is solidly authorised by EFSA.
- Teeth - It contributes to the maintenance of normal teeth, again via its role in calcium metabolism.
- Calcium and phosphorus absorption - It supports normal absorption and utilisation of calcium and phosphorus, two minerals you cannot afford to waste.
No supplement will cure or treat any disease. But walking around deficient in something this fundamental is not a neutral state.
Why 400 IU Is a Floor, Not a Target
The NHS 400 IU figure was set to address acute deficiency in the general population. It is a minimum, not a recommended optimal intake. Many nutrition practitioners working with UK adults consider a daily intake of 1000 IU to 4000 IU to be far more appropriate for maintaining reasonable blood levels through winter, depending on the individual.
Several factors affect how much you personally need.
- Skin tone - Melanin reduces UVB absorption, so people with darker skin synthesise less vitamin D from the same sun exposure.
- Body weight - Vitamin D is fat-soluble and can be sequestered in body fat, meaning higher body weight is often associated with lower circulating levels.
- Age - Skin becomes less efficient at synthesising vitamin D as you get older. Adults over 60 often need meaningfully more.
- Gut health - Because vitamin D is fat-soluble, anything that reduces fat absorption can reduce how much you actually absorb from a supplement.
- Starting level - If your blood level is already very low, a maintenance dose will take much longer to lift you than if you are only slightly below the sufficient range.
If you are on medication or have a health condition, talk to your GP before starting a higher-dose supplement. With fat-soluble vitamins, your body stores what it takes in, so that conversation genuinely matters.
Test, Do Not Guess
This is the part most people skip. They buy a supplement, take it for a few months, feel a bit better or not, and never actually know what their blood level was before or after. That is a waste of money and effort.
A vitamin D blood test measures your serum 25-hydroxyvitamin D level. Your GP can request one. If they will not, private home finger-prick tests are widely available and reasonably priced. Getting a baseline reading costs very little compared to months of taking the wrong dose.
| Blood Level (nmol/L) | What It Means | Typical Action |
|---|---|---|
| Below 25 | Severely deficient | GP review recommended before self-supplementing |
| 25 to 50 | Deficient | Higher-dose supplementation usually appropriate |
| 50 to 75 | Insufficient | Moderate supplementation with retesting |
| 75 to 150 | Sufficient | Maintenance dose to hold the level through winter |
| Above 250 | Potentially excessive | Reduce dose and retest, talk to your GP |
Most UK adults who test in autumn land somewhere in the insufficient range. That is not alarming. It is just information you can act on.
Why You Should Pair Vitamin D3 With K2
Vitamin D supports calcium absorption. Vitamin K2 helps direct that calcium toward bones and teeth rather than soft tissue. If you are taking a meaningful dose of vitamin D over the long term, pairing it with K2 is sensible practice. I stock Viridian Vitamin K2 Vegan 60 Capsules because the quality is consistent and the MK-7 form has good bioavailability compared to MK-4.
View in the shop
Choosing the Right Vitamin D Supplement in the UK
Not all vitamin D supplements are the same. A few things to look for when buying.
- D3 over D2 - Cholecalciferol (D3) is the form your skin makes and raises blood levels more effectively than D2, which appears in some products but is generally considered inferior for maintaining levels.
- Dose clarity - The label should state IU or micrograms clearly. 10 micrograms equals 400 IU. A 4000 IU supplement contains 100 micrograms. Do the arithmetic before you buy.
- Vegan source - Most D3 comes from lanolin in sheep's wool. If you are vegan, look for D3 sourced from lichen. The Viridian Vegan Vitamin D3 4000iu (from Lichen) Capsules is the one I point vegans toward in the shop. Lichen-derived D3 performs comparably to lanolin-derived, and Viridian's quality control is reliable.
- Oil-based capsules - Because vitamin D is fat-soluble, taking it with a meal containing some fat improves absorption. Dry tablets are less ideal.
- Clean excipients - Check the extras on the label. A product with minimal fillers is sensible when you are taking something daily for months at a time.
FAQ
Is it safe to take 4000 IU of vitamin D every day?
For most healthy adults, 4000 IU daily is within a reasonable range and sits at the tolerable upper intake level set by EFSA for adults. That said, if you have a health condition, take medications, or are pregnant, talk to your GP before starting any higher-dose supplement. Testing your levels before and after gives you the clearest picture of what is appropriate for you.
Can I get enough vitamin D from food?
Dietary sources including oily fish, egg yolks, and fortified foods contribute something, but not nearly enough to maintain adequate blood levels through a UK winter. Food alone is not a reliable substitute for supplementation if you live at this latitude and spend most of your time indoors.
When is the best time to take a vitamin D supplement?
With your largest meal of the day is the practical answer, particularly if that meal contains some fat. Vitamin D is fat-soluble, so absorption is better alongside dietary fat. Morning or lunchtime suits most people better than last thing at night, though the difference in timing is not dramatic either way.
How long does it take to raise a low vitamin D level?
It depends on how low you are starting and what dose you take. Starting from a deficient level, consistent supplementation at an appropriate dose will typically shift things over eight to twelve weeks. Testing at the start and retesting after three months gives you a clear comparison. Do not just guess and hope.
Does vitamin D work differently for older adults?
Yes, in a couple of important ways. Skin becomes less efficient at synthesising vitamin D with age, and kidney function, which is involved in converting vitamin D to its active form, also changes over time. Adults over 60 often need a higher dose to reach and maintain the same blood level as a younger person. It is one of the reasons I rarely suggest 400 IU to anyone over 50 who walks through the door.