December 16, 2025, 3:01 pm | Read time: 5 minutes

Advertising campaigns and social media content have made many people aware that a large portion of the population in Germany is not sufficiently supplied with the “sunshine vitamin.” The demand for supplements is therefore high. Many take supplements prophylactically, not because a deficiency has been proven. According to “Stiftung Warentest,” this could be more harmful than beneficial. A review of 25 vitamin D products found that only two are “unconditionally” recommended in terms of dosage and ingredient composition. The testers even explicitly advise against five products, stating that “long-term use could harm health rather than benefit it.”¹

The Products Tested by “Stiftung Warentest”

• Abtei Vitamin D3 2500 IU + Zinc + Selenium
• Abtei Vitamin D3 3000 IU
• Alsiroyal Vitamin D3 Plant-Based + K2 Melt Tablets
• Cefavit D3 1000 IU
• Cefafit D3 K2 Mg 2000
• Dekristolvit D3 2000 IU
• Dekristolvit D3 4000 IU
• dm Mivolis Vitamin D3 1000 IU
• dm Mivolis Vitamin D3 Weekly Depot 5600 IU
• Doppelherz Aktiv Vitamin D3 2000 IU
• Doppelherz System Vitamin D3 7000 IU Plant-Based
• GSE Vitamin D Bio
• GSE Vitamin D3 Bio
• Hübner Vitamin D3 800 IU
• Hübner Vitamin D3 Compact 2000 IU
• Natural Elements Vitamin D3/K2 Drops
• Raab Vitalfood D3 + K2 Vitamins
• Rossmann Altapharma D3 + K2 Drops
• Rossmann Altapharma Vitamin D3 2000 IU
• Rotbäckchen Vital Vitamin D
• Sanotact Vitamin D 3200 IU
• Taxofit Vitamin D3 2500 IU
• Tetesept Vitamin D3 1000 Weekly Depot
• Vitamin D3 2000 High Dose
• Vigantolvit Vitamin D3 2000 IU

“Among the tested products are tablets, capsules, drops with vitamin D3 or D2, and a juice-based drink. In the test, we included products with daily doses of 200 to 4000 international units (IU) of vitamin D and also preparations with additional active ingredients like vitamin K2, magnesium, selenium, or zinc. We assess whether these combinations of active ingredients are sensible,” says “Stiftung Warentest” about the test selection. “We did not test high-dose medications with vitamin D like Dekristol 20,000. These medications are approved for treating a medically diagnosed vitamin D deficiency, which can lead to bone softening and osteoporosis.”

What to Consider When Taking Vitamin D Supplements

Anyone considering taking a vitamin D supplement should—especially if doing so independently—opt for a low dosage. The Federal Institute for Risk Assessment (BfR) advises that no more than 20 micrograms or 800 international units (IU) of vitamin D should be consumed daily through supplements. “To reach a level of 35 to 40 nanograms per milliliter (a level below 30 nanograms per milliliter is considered deficient, A. d. R), I need 4000 IU daily from November to April,” explained nutritionist Prof. Dr. Nicolai Worm to FITBOOK in an earlier article.

Of the 25 supplements reviewed by “Stiftung Warentest,” most are overdosed. Five even failed with the verdict “not suitable” because they contain so much vitamin D that kidney damage could occur with long-term use.

By the way: Depot supplements, which are taken, for example, only once a week, are viewed critically by the testers because dosage errors can easily occur. If taken more than once a week by mistake, overdoses can happen.

Who Is at Risk for Vitamin D Deficiency?

According to data from the Robert Koch Institute (RKI), 44 percent of adults in Germany are well supplied with vitamin D.² Taking additional vitamin D supplements does not benefit them.

However, there are groups at higher risk of not being adequately supplied with vitamin D, such as people who get little sunlight. “For example, bedridden individuals or people who completely cover themselves,” said Daniela Krehl, nutrition expert at the Consumer Center Bavaria, in response to a dpa inquiry.

Other risk groups according to the RKI:

• older adults
• infants
• people with certain conditions, such as chronic diseases of the parathyroid, kidney, or gastrointestinal tract

Always Advisable: A Blood Test

The only way to determine how well the body is actually supplied with vitamin D is through a blood test. If you’re unsure, you can discuss the issue with your doctor.

If a deficiency is suspected, the health insurance covers the cost of a blood test. Otherwise, you have to pay out of pocket. Tip: The end of winter is not a good time to determine the level. At that time, stores are depleted, and the values are not very meaningful.

More on the topic

The Best Supplements for Endurance and Performance

Research Context Does a Vitamin D Deficiency Affect Muscle Strength?

What Does Our Body Need Vitamin D For?

Our body needs vitamin D, among other things, for bone stability. Vitamin D ensures that the body can absorb calcium from the gastrointestinal tract and incorporate it into the bones. It is also important for muscle function, hormone metabolism, and immune defense.

Where Does Our Body Get Vitamin D From?

There are foods that provide us with vitamin D, such as fatty sea fish like salmon and mackerel, plant oils, and dairy products. “But you can’t meet the requirement with these,” said Prof. Johannes Wechsler, president of the Federal Association of German Nutritionists, according to dpa. We get only about ten percent of our needs from food.

The rest is produced by the body itself, which requires sunlight hitting the skin. How much vitamin D a body can produce this way depends on many factors: season, latitude, time of day, and skin type—and also whether we have applied sunscreen.

Various professional societies have developed recommendations on how much sun exposure is sufficient to produce enough vitamin D.³ According to this, it is sufficient to expose the face, hands, and arms to the sun two to three times a week, uncovered and without sunscreen. And for half the time, it would normally take to get a sunburn without protection.

By the way: The sun we soak up in summer benefits us in winter as well. The body stores vitamin D in fat and muscle tissue.⁴