Vitamin D helps your body absorb and use calcium and phosphorus, and it contributes to the maintenance of normal bones, teeth and muscle function and to the normal function of the immune system. Your skin makes most of it from sunlight, but in Switzerland the sun is too weak from about October to March, so blood levels often drop in winter. Adults need 15 to 20 µg (600 to 800 IU) a day when the skin makes none, and more than 100 µg a day is too much.
Key facts about vitamin D
- Reference intake: the D-A-CH reference value for adults is 20 µg (800 IU) a day when the skin produces no vitamin D; EFSA sets 15 µg. The Swiss Federal Commission for Nutrition recommends 15 µg up to age 59 and 20 µg from age 60.
- The nutrient reference value (NRV) printed on EU and Swiss labels is 5 µg.
- Safe upper level (EFSA): 100 µg (4,000 IU) a day for adults and adolescents from 11 years, 50 µg for children aged 1 to 10.
- Status is measured as 25-hydroxyvitamin D in the blood; 50 nmol/l (20 ng/ml) or more is considered adequate, below 30 nmol/l (12 ng/ml) a deficiency.
- Few foods are rich in it: a tablespoon of cod liver oil provides about 34 µg, a portion of farmed salmon or trout 13 to 16 µg, an egg about 1 µg.
What does vitamin D do in the body?
Vitamin D works more like a hormone than most vitamins. Whether it comes from the skin or from food, the liver first turns it into 25-hydroxyvitamin D (calcidiol), the storage form your doctor measures. The kidneys and other tissues then convert it into calcitriol, the active form. Calcitriol binds to vitamin D receptors that are found in almost every tissue and switches genes on or off, above all those that control how much calcium the gut absorbs.
In the EU and Switzerland the following health claims are authorised. Vitamin D contributes to:
- normal absorption and utilisation of calcium and phosphorus;
- normal blood calcium levels;
- the maintenance of normal bones;
- the maintenance of normal muscle function;
- the maintenance of normal teeth;
- the normal function of the immune system;
- and it has a role in the process of cell division.
Bones and teeth
Without enough vitamin D the gut absorbs only a fraction of the calcium in your food, however much you eat. Bones then cannot mineralise properly: severe, long-lasting deficiency causes rickets in children and osteomalacia (soft bones) in adults. Calcium and vitamin D work as a pair, which is why our guide to calcium needs and the best food sources is the natural next read.
Muscles
Muscle cells carry vitamin D receptors, and muscle weakness is a typical sign of marked deficiency, especially in older adults. Vitamin D contributes to the maintenance of normal muscle function.
Immune system
Many immune cells can activate vitamin D themselves, which is why researchers study vitamin D status in relation to infections. Vitamin D contributes to the normal function of the immune system. Trials do not show that extra vitamin D protects people who already have adequate levels against colds or other illnesses. For the full picture, see our overview of vitamins and minerals for a healthy immune system.
Is vitamin D really a vitamin?
Strictly speaking, not quite. A vitamin is a substance the body cannot make, but your skin produces vitamin D itself when UVB light reaches it. It was named a vitamin a century ago, when cod liver oil was linked to healthy bones in children. Today it is better described as a prohormone: the starting material for the hormone calcitriol.
How does the body get vitamin D in Switzerland?
Sunlight and season
Under good conditions the skin supplies 80 to 90 % of the vitamin D you need. How much it makes depends on latitude, season, time of day, skin type, age and how much skin is uncovered. At Swiss latitudes the UVB in sunlight is strong enough only from about March or April to September. In summer, exposing your face, hands and arms without sunscreen two or three times a week, for about half the time it would take you to burn, is enough according to the DGE. Never let your skin burn.
From October to March the sun is too low for meaningful production. Summer stores last a few weeks to months, so levels are often lowest in late winter.
Food
Food provides only 10 to 20 % of the usual supply, because few foods contain much vitamin D.
| Food and portion | Vitamin D (approx.) |
|---|---|
| Cod liver oil, 1 tablespoon (14 g) | 34 µg |
| Trout, farmed, cooked, 85 g | 16 µg |
| Salmon, cooked, 85 g | 13 to 14 µg |
| White mushrooms exposed to UV light, 35 g | 9 µg |
| Fortified plant drink or milk, 250 ml | 2.5 to 3 µg |
| Sardines, canned, 2 fish | 1.2 µg |
| Egg, 1 large | 1.1 µg |
| Tuna, canned, 85 g | 1 µg |
| Ordinary mushrooms, not UV-treated, 35 g | under 0.1 µg |
If you eat no fish, fortified foods and UV-exposed mushrooms are the main dietary options, which is why a supplement is worth considering in winter.
How is vitamin D absorbed, and when should you take it?
Vitamin D is fat-soluble. It is absorbed in the small intestine together with fat, so take a supplement with a meal that contains some fat, for example breakfast with nuts or yoghurt, or lunch. Morning or evening matters less than taking it regularly.
Blood levels do not change overnight. With a steady daily intake, 25-hydroxyvitamin D rises over several weeks and levels off after roughly two to three months, so a follow-up test makes sense after about three months at the earliest.
What lowers vitamin D levels?
- little time outdoors, covered skin or consistent use of high-factor sunscreen;
- darker skin, which needs longer sun exposure to make the same amount;
- older age, because the skin produces less vitamin D;
- a higher body weight, as vitamin D is stored in fatty tissue;
- conditions that reduce fat absorption (coeliac disease, Crohn's disease) and chronic liver or kidney disease;
- certain medicines, for example some anti-epileptic drugs, long-term glucocorticoids and the weight-loss drug orlistat.
Vitamin D2 or D3: which is better?
Both forms are converted into the same active hormone. Vitamin D3 (cholecalciferol) is the form your skin makes; in supplements it usually comes from lanolin in sheep's wool, or from lichen in vegan products. Vitamin D2 (ergocalciferol) is produced by yeasts and mushrooms exposed to UV light and is vegan by nature. Studies suggest D3 raises blood levels somewhat more reliably than D2, especially at high, infrequent doses. At moderate daily amounts both contribute to your intake, and for most people regular use matters more than the form.
Can you take too much vitamin D?
Yes, from supplements but not from sunlight: the skin regulates its own production. Very high intakes over weeks or months can raise blood calcium (hypercalcaemia), with nausea, thirst, frequent urination, confusion and, in severe cases, kidney damage. Stay below 100 µg a day from all supplements combined unless your doctor prescribes a higher dose. Weekly or monthly high-dose products and vitamin D with vitamin K2 belong in a conversation with your doctor or pharmacist, especially if you take blood thinners.
Vitamin D in Sanbera Daily Essential formulas
Both Daily Essential formulas contain vegan vitamin D2. Per daily serving of three tablets, Daily Essential Women provides 3.22 µg (64 % NRV) and Daily Essential Men 3 µg (60 % NRV), together with calcium (120 mg, 15 % NRV), magnesium and vitamin A. Vitamin D contributes to the maintenance of normal bones and muscle function and to the normal function of the immune system. The Nightly Reload formulas contain no vitamin D.
To be clear: this is a base contribution, not the full 15 to 20 µg recommended for winter. If your blood level is low or your doctor advises a separate vitamin D product, you can combine the two and still stay far below the 100 µg upper level. Vitamin A plays a different role; read about the benefits of vitamin A and how much you need.
Frequently asked questions
What does vitamin D do for your body?
Vitamin D lets your gut absorb calcium and phosphorus and keeps blood calcium at a normal level. It contributes to the maintenance of normal bones, teeth and muscle function and to the normal function of the immune system, and it has a role in cell division. In children it is needed for normal bone growth. Your skin makes most of it from summer sunlight.
What happens if you have a vitamin D deficiency?
A mild deficiency often causes no clear symptoms. Over time, calcium absorption falls, which can lead to bone pain, muscle weakness and, in severe cases, soft bones (osteomalacia) in adults or rickets in children. Tiredness is often blamed on vitamin D, but it has many causes. Only a blood test for 25-hydroxyvitamin D shows whether your level is low.
Which vitamin D blood levels are normal?
Most European bodies regard a 25-hydroxyvitamin D level of 50 nmol/l (20 ng/ml) or more as adequate for bone health. Values below 30 nmol/l (12 ng/ml) indicate a deficiency, and 30 to 50 nmol/l an insufficient supply. The US National Institutes of Health note possible adverse effects above about 125 nmol/l (50 ng/ml). Ask your doctor to interpret your result, as targets can differ for some patients.
Is vitamin D good for your skin?
Skin cells both make vitamin D and respond to it, and vitamin D has a role in the process of cell division, which skin renewal depends on. There is no authorised health claim for vitamin D and skin, however. Prescription creams for psoriasis use vitamin D analogues, which is a medical use. For skin nutrients, see our article on the best vitamins for your skin.
Why is vitamin D often combined with magnesium or vitamin K2?
Magnesium contributes to the maintenance of normal bones and is involved in the enzymes that activate vitamin D; read more in our article on the benefits of magnesium. Vitamin K contributes to the maintenance of normal bones too. At ordinary doses most people do not need K2 with vitamin D; anyone taking anticoagulants must ask their doctor before using vitamin K.
Can vitamin D make you happy?
Vitamin D has no authorised claim for mood. People with low mood often have lower vitamin D levels, partly because they spend less time outdoors, but trials giving vitamin D supplements show mixed results. Winter blues and depression deserve proper attention: if low mood lasts more than two weeks, speak to your doctor rather than relying on a supplement.
Sources
- German Nutrition Society (DGE): Questions and answers on vitamin D
- German Nutrition Society (DGE): Reference values for vitamin D
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2016): Dietary reference values for vitamin D
- EFSA Panel on Nutrition (2023): Scientific opinion on the tolerable upper intake level for vitamin D
- National Institutes of Health, Office of Dietary Supplements: Vitamin D, Health Professional Fact Sheet
- European Commission: EU Register of nutrition and health claims
This article is for general information and does not replace advice from a doctor or pharmacist. Food supplements are not a substitute for a varied, balanced diet and a healthy lifestyle.