Which vitamins to take in autumn:
what blood tests show and what the label is allowed to say
Autumn doesn't change your body. It changes the sun. From September, the angle at which light hits Romania drops so far that your skin can no longer make vitamin D, however long you stay outside. That's the only need that genuinely changes with the season. September tiredness and colds have more causes than the supplement shelf will sell you.
What changes in autumn:
the light, not your body
Vitamin D is made in the skin, under the action of ultraviolet B rays. The problem is that this radiation doesn't reach the ground all year round, however clear the sky is. In what has become a classic study, Webb, Kline and Holick measured in 1988 how much cholecalciferol actually forms in the skin at different latitudes. Their conclusion: at 42 degrees north, in other words in Boston, UVB radiation is insufficient for vitamin D synthesis from November until early March. Ten degrees further north, in Edmonton, the dead window stretches from October to April.
Romania lies between 43.6 and 48.3 degrees north. North of Boston, south of Edmonton. There's no study that pins down the exact starting month for Constanța or for Baia Mare, so nobody can honestly give you a fixed date. The direction, on the other hand, is clear: the vitamin D winter here is longer than Boston's, not shorter.
Your plate won't fix it. Vitamin D is concentrated in very few foods: oily fish, egg yolk, liver. To cover your daily needs from food, you'd have to eat oily fish almost every day, which hardly anyone does.
Now the part that seasonal marketing skips: your need for vitamin C, zinc or iron doesn't increase because autumn has arrived. What changes is something else. You spend more time indoors, so you're exposed to respiratory viruses more often. Your schedule gets tighter, so you sleep less. And the tiredness you blame on the season often comes from sleep, not from vitamins.
The only nutrient whose availability genuinely changes with the season is vitamin D, because its main source is the sun, not your plate. Everything else remains a conversation about diet, sleep and, where relevant, what your blood tests show.
Start with a blood test,
not a shelf
The test is called 25(OH)D, short for 25-hydroxyvitamin D. It's done from a blood sample, doesn't require fasting and is available in any laboratory in Romania. It's the only one that actually changes your decision, because it tells you whether you're starting from 12 or from 32.
The guideline for assessing vitamin D status in adults, used in Romania's public health network, works with the thresholds below.
| 25(OH)D value | What it's called | What comes next, according to the guideline |
|---|---|---|
| below 10 ng/ml | severe deficiency | Below 25 nmol/l. To be discussed with your doctor. The guideline mentions regimens of 2,000 to 10,000 IU a day for 4 to 6 weeks, or 50,000 IU a week for 8 weeks. |
| 10 to 20 ng/ml | mild deficiency | Between 25 and 50 nmol/l. Ongoing supplementation with 600 to 1,000 IU a day. |
| above 20 ng/ml | sufficient level | Above 50 nmol/l. The guideline notes that 50 nmol/l covers the needs of 97.5% of the population. |
| above 100 ng/ml | toxic range | Above 250 nmol/l. Supplementation is stopped and medical advice is sought. |
For the general adult population without symptoms, the same guideline mentions 600 to 1,000 IU a day during the cold season. Remember that figure; we'll come back to it when we get to what's written on the boxes.
Testing isn't necessary for everyone. The guideline recommends it especially for people with low sun exposure, musculoskeletal conditions, absorption disorders, kidney failure, endocrine diseases or obesity. If none of these applies to you and you still want to know where you're starting from, the test costs about as much as a box of supplements and tells you far more than the box does.
If you only want the dosing part, common mistakes included, we've written separately about how much vitamin D3 you need and how to tell, and about pairing it with K2, also separately, in vitamin D3 and K2: why they're taken together.
What the label is allowed to say,
and what it isn't
In the European Union, you can't say whatever you think is true about a supplement. You can only say what's authorised, and the list is public. The basic rule has two halves, and both matter: a health claim is attributed to a nutrient, never to the plant or the ferment, and only if the product contains a significant amount of that nutrient.
For autumn, four authorised claims cover almost the whole discussion.
| Nutrient | What the label is allowed to say | What it means in practice |
|---|---|---|
| Vitamin D | contributes to the normal function of the immune system and to the maintenance of normal muscle function | The only immunity-related claim that makes sense in a seasonal product, because this is exactly the nutrient that drops in winter. |
| Vitamin C | contributes to the reduction of tiredness and fatigue | It refers to tiredness, not to colds. The difference is big, and almost every advert ignores it. |
| Zinc | contributes to normal cognitive function | Zinc has several authorised claims, but none of them says it shortens a cold. |
| Vitamin B6 | contributes to the regulation of hormonal activity | Useful to know if the product contains it in a sufficient amount, not as a general argument. |
With this list in your head, you can read any box in the pharmacy like an inspector. Tap each claim below: all of them are taken from real packaging or adverts.
It isn't an authorised claim in any form. The authorised wording talks about the normal function of the immune system and belongs to specific nutrients, including vitamin D, vitamin C and zinc, provided the product contains them in a significant amount. The difference between “strengthens” and “contributes to the normal function” isn't a subtlety of language, it's the difference between legal and illegal.
Doubly problematic. On top of the unauthorised claim, it adds a promise of speed, and wording that suggests a pace or duration of effect is regulated separately. “Boosted immunity” isn't even a quantity anyone can measure. We've unpacked the subject at length in how to boost your immunity fast.
“Detox” isn't an authorised claim, and it isn't even a scientifically defined notion. It's also one of the phrasings that advertising platforms reject for supplements.
It sounds gentle and medical at the same time, but it's still an unauthorised health claim. It doesn't matter how politely it's worded or how often you see it.
It's the authorised wording, word for word. The condition is that the product contains a significant amount of vitamin D. If the claim is on the label but vitamin D appears in a tiny amount in the nutrition table, you have a product hiding behind a correct sentence.
Authorised, with the same quantity condition. Note what it actually says: tiredness, not colds. A product that uses this claim and then puts a drawing of a thermometer on the box is pulling exactly the trick we're talking about.
It isn't a health claim, it's a fact about the product. The chemical form, the dose and the serving. The kind of information that actually helps you compare two boxes, unlike adjectives.
If the box says something that is neither an authorised claim nor a verifiable fact about the ingredient, you're not looking at information nobody else has. You're looking at an advert that breaks the regulation, and that says something about the rest of the product too.
Doses:
where they help and where the ceiling is
The reference intake and the upper limit are two different things, and confusing them is why people end up taking ten times more than they need every day. The benchmark tells you where sufficiency begins. The ceiling tells you where safety ends.
| Nutrient | Daily benchmark for adults | Daily upper limit |
|---|---|---|
| Vitamin D | 600 to 1,000 IU in the cold season, for an adult without symptoms, according to the Romanian guideline | 100 µg, which is 4,000 IU The tolerable upper intake level, maintained by EFSA in 2023 |
| Vitamin C | 95 mg for women, 110 mg for men, the EFSA reference intake from 2013 | no limit set EFSA could not derive a limit due to a lack of data. As a guide, it indicated that 1,000 mg a day from supplements does not usually cause unpleasant digestive effects |
| Zinc | between 7.5 and 16.3 mg, depending on how much phytate your diet contains | 25 mg A limit set by the European Commission's Scientific Committee on Food in 2003 |
A calculation that concerns us too. ROOTFUL vitamin D3 gummies contain 4,000 IU per serving, which is exactly the EFSA ceiling for adults. Not above it. But it means you don't combine them with a multivitamin or another source of vitamin D without adding up the figures. The same arithmetic applies to zinc: our vitamin C, zinc and D3 gummies contain 22.74 mg of zinc per serving, below the 25 mg ceiling, but close enough that a second zinc supplement would take you off the chart.
The adding-up rule applies to any brand, not just ours. If you take three different products, you add up what's in them. We've put together a complete timetable, including what clashes with what, in which supplements shouldn't be taken together.
Before you increase any dose. Regimens to correct a severe deficiency are done with your doctor, not from an article, however well documented. During pregnancy and breastfeeding, any supplement should be discussed with your doctor beforehand. For children, doses differ from adult doses and aren't portioned out “by eye” from a parent's box. If you are undergoing treatment, have a kidney or liver condition, or have had high calcium levels, ask your doctor before supplementing with vitamin D. Do not exceed the recommended daily dose on the packaging.
What a supplement
doesn't fix
This is the part where we make life harder for ourselves.
A supplement doesn't make up for five hours of sleep. It doesn't replace a diet with vegetables and protein. And it doesn't make your immunity “stronger”, because stronger immunity isn't a quantity anyone can measure; it's a slogan that sells well in September.
What a vitamin D supplement does is much simpler and much more limited: it covers an intake the sun can no longer cover from autumn to spring. That's it. It's useful precisely because it's limited and predictable.
We sell the Immunity + Digestion Ritual, D3 4,000 IU gummies in the morning and apple cider vinegar and kombucha gummies during the day. The honest part, said before you go looking for it yourself: only the first half has an authorised health claim. Apple cider vinegar and kombucha have none in the European Union, so you won't read any promises about them from us. What we can tell you is what they contain, in what amount, how they're made and how to take them.
If you want to understand why we talk about immunity as a twelve-month habit rather than a three-month one, we've written about it in immunity 365, not just in winter.
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