Vitamin D in Autumn: When to Start, How Much Is Safe Without a Test, and Who Needs It Most

Every October the pharmacy sees the same thing. “Give me vitamin D, the strongest one.” “Can I take 10,000?” “My friend takes 50,000 once a week, do I need that too?”

Let’s stay calm. Vitamin D is needed, and autumn is a good time to think about it. Here, though, more does not mean better. Let’s look at when to start, how much to take and where the safe zone ends.

Why vitamin D becomes a problem in autumn

The main human source of vitamin D is the skin. UVB light triggers vitamin D3 synthesis there. For that, the sun has to be high enough in the sky.

Back in 1988, researchers showed that in Boston (42° north) the skin makes no vitamin D at all from November to February, no matter how much time a person spends outdoors. Kyiv lies at 50°, Lviv at 49.8°, Odesa at 46.5°. So in Ukraine the “vitamin D winter” is even longer, roughly from October to March.

The body’s summer stores of vitamin D run down within weeks to months. By the end of winter, most people’s blood 25(OH)D is noticeably lower than in September.

Food provides little vitamin D. It is found in oily sea fish (salmon, mackerel, herring), egg yolk, cod liver and, to some extent, mushrooms grown in sunlight. Getting the daily amount from food alone would mean eating salmon almost every day.

How much vitamin D you need and where the safe limit is

Two numbers matter here. The first is how much covers your needs. The second is the maximum you can take without risk. Both are set by the European Food Safety Authority (EFSA), and Ukrainian dietary supplement requirements now refer directly to the upper limit.

A quick cheat sheet: 1 µg of vitamin D equals 40 IU. So 1,000 IU is 25 µg and 2,000 IU is 50 µg.

The upper limit applies to total intake: food, fortified products and all supplements together. If you take a multivitamin and a separate vitamin D, add the doses up.

Since April 2026, a dietary supplement in Ukraine may not contain more vitamin D per daily portion than the EFSA upper limit, which is 100 µg for adults. We covered this in detail in our article on dietary supplement requirements in Ukraine. So “loading” doses of 10,000 IU a day are found only in medicines prescribed by a doctor.

Do you need a vitamin D test

The test that shows your vitamin D stores is called 25(OH)D (25-hydroxyvitamin D). Most laboratories consider a level below 20 ng/mL (50 nmol/L) insufficient for bone health.

For healthy people without risk factors, the US Endocrine Society advised in 2024 against routine testing. The logic is simple: if someone takes a normal preventive dose, the test result rarely changes anything.

The table shows who really does need a test.

If you see yourself in the table, start with a doctor and a test. If not, a normal preventive dose in autumn and winter does not need any prior testing.

Which form of vitamin D to choose

D3 or D2. In a 2012 meta-analysis, cholecalciferol (D3) raised blood 25(OH)D more effectively than ergocalciferol (D2). That is why most supplements contain D3. Vegans should look for D3 from lichen, because standard D3 is made from lanolin in sheep’s wool.

Drops, capsules or tablets. There is no real difference in effectiveness. Drops suit children and anyone who needs a precise dose. Oil capsules are convenient for adults.

Daily or weekly. In studies on preventing respiratory infections, daily small doses worked better than rare large “loading” doses. So for prevention I would choose a daily option.

What the label may say. Vitamin D has officially authorized health claims, such as “contributes to the normal function of the immune system” or “contributes to the maintenance of normal bones.” Promises like “treats,” “protects against flu” or “instead of a vaccine” are banned on dietary supplements.

How to take vitamin D so it is absorbed

Vitamin D is fat-soluble. In a 2015 study, people who took it with a meal containing fat absorbed noticeably more than those who took the capsule with water before a fat-free breakfast. The simplest rule: take vitamin D with your most substantial meal.

A few practical points:

keep track of your total dose if you take a multivitamin; store drops as directed, because vitamin D is sensitive to light and heat; do not double the dose if you miss a day; if you take thiazide diuretics, cardiac glycosides or calcium supplements, discuss vitamin D with your doctor.

For the mineral that vitamin D works best with, see our piece on magnesium and the brain.

When there is too much vitamin D

Vitamin D overdose is almost always linked to supplements: you cannot get it from the sun or normal food. It usually comes from long-term doses well above 4,000 IU or a mistake with concentrated drops.

Excess vitamin D raises blood calcium. Symptoms include nausea, thirst, frequent urination, weakness, constipation and, in severe cases, kidney damage. If you have taken high doses for a long time and notice something like this, see a doctor and get your calcium and 25(OH)D checked.

Frequently asked questions

Conclusions

Most people in Ukraine do need vitamin D in autumn: from October to March the skin makes almost none, and food provides little. For a healthy adult, 15 µg (600 IU) a day is enough, and the safe upper limit from all sources is 100 µg (4,000 IU).

Healthy people do not need a test before taking a normal preventive dose, but risk groups do. Choose D3, take it daily with a meal that contains some fat, and count your total dose.

And if someone recommends 50,000 IU “loading” doses without a test or a doctor, this is not a case where more is better.

About the Author

Kateryna Braitenko is a Ukrainian journalist and author specializing in writing articles for pharmaceutical publications. She holds a philology degree from Donetsk National University and a pharmaceutical degree from the National Pharmaceutical University in Kharkiv. She lives in Kyiv and continues her career, covering relevant issues in medicine and pharmaceuticals.