Nutrients
A comprehensive Q&A guide addressing the most important vitamin D questions: from optimal blood levels to dosage, safety, and nutrient synergies. This science-backed resource helps you optimize your vitamin D status.
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We regularly receive emails with questions about vitamin D. Today we're providing a comprehensive Q&A guide to address the most important vitamin D questions thoroughly. This should clarify most issues on the topic. Enjoy!
One note: Feel free to print or share this. The information is essential for many people, and especially important for you – each fall, winter, and spring!
According to the Robert Koch Institute, a normal status is around 20 ng/ml (= 50 nmol/L). However, multiple professional organizations, including the Endocrine Society and vitamin D discoverer Michael F. Holick himself, (recent publication in Nature) recommend a minimum of 30 ng/ml (= 75 nmol/L) to maximize vitamin D's effects on calcium, bone, and muscle metabolism.
Yes. First, fatty tissue acts as a «sink» for vitamin D – it readily accumulates there. Second, higher body mass increases overall demand. Studies show that people with significant obesity may need two to three times more vitamin D, while overweight individuals generally need about 50% more.
Not necessary. Perhaps once at the beginning to establish a baseline, but your body's own feedback is the best measurement tool. Most people achieve adequate levels with around 2,000 IU daily – a very safe dose you can maintain throughout the dark season without any concerns.
There are two approaches to raising vitamin D levels, with minimal practical difference. The first is taking your daily requirement consistently – this resolves deficiency quickly, though it takes time to reach target levels. The second is taking large doses once or multiple times to reach target levels quickly, then maintaining with a lower dose ("loading"). For this approach, specialized vitamin D calculators can account for body weight and current levels. Important: vitamin D follows saturation kinetics, not linear dose-response. This means small amounts have substantial effect, and conversely, very large doses rarely cause true toxicity. See a dose-response curve here.
A recent peer-reviewed article published in the prestigious journal Nature recommends 400–1,000 IU daily for infants up to one year old.
As a reminder: vitamin D is naturally synthesized in skin when UV exposure reaches sufficient intensity. It's well-documented that from October through March at our latitudes (including Switzerland), UV levels are too low to produce meaningful vitamin D in skin. Here's a figure illustrating this.
Not at all – study after study confirms that Europeans, particularly in winter months, don't have adequate vitamin D. Germany's Robert Koch Institute showed in a 2015 study that 80% of the population doesn't reach the recommended 20 ng/ml – and even fewer reach 30 ng/ml. The picture in Switzerland looks similar: a Federal Office of Public Health (BAG) study found that more than 60% of the population is vitamin D deficient during winter months. This unprecedented deficiency is paradoxically downplayed here as well. Quite bewildering.
Better than nothing either way. However, evidence increasingly suggests that single high doses accelerate breakdown, while consistent smaller doses work better. There's also discussion about whether daily vitamin D intake might work differently than the storage form. Our recommendation: daily smaller amounts rather than large doses at long intervals.
Doesn't matter. Vitamin D is always well-absorbed and raises blood levels regardless of timing. That said, taking it with some fat aids absorption.
Theoretically yes, but vitamin D is likely one of the safest vitamins available. In summer, the skin synthesizes very high amounts naturally. The dose considered extremely high here (about 10,000 IU) is produced in minutes of summer sun exposure. Humans have clearly evolved mechanisms to handle substantial vitamin D. That said, doses exceeding 10,000 IU daily for extended periods should still be avoided.
Not us – but blood work from a close relative showed that a tan can be deceiving. After a sunny summer with good tanning, their level was only 11.8 ng/ml – below 20 ng/ml and technically deficient.
The gaps between national guidelines are enormous. For comparison: Germany and Austria have the lowest recommendations in Europe – and Switzerland, with the BAG's daily reference of 600 IU for adults, sits at a similarly cautious level. Countries like Belgium, Denmark, Ireland, and Norway recommend substantially higher intakes. Why? Remember: there's no single "truth" in science. The same evidence gets interpreted differently by different people, resulting in very different recommendations. Across the German-speaking region, caution typically dominates.
Your doctor may assume the body can mobilize sufficient vitamin D from fatty tissue during winter – unfortunately untrue. The fact is, without supplementation or vitamin D-rich foods (like fatty fish), you can't meet your needs or maintain adequate levels. Notably, most people don't even reach normal levels in summer.
Not necessarily. Vitamin D appears to drive production of vitamin K-dependent proteins, which theoretically increases vitamin K demand. However, no studies show that higher K intake improves vitamin D effectiveness. It's a good idea to meet your K needs – K2-MK7 works about four times better than K1. That's why we include both in our multi and our D/K2 combination.
Definitely yes! Research on traditional African populations (like the Hadza) shows pregnant women there often have levels around 60 ng/ml. Evidence suggests pregnant women need at least 20 ng/ml (= 50 nmol/L) for adequate supply. Studies confirm that up to 4,000 IU daily is safe for pregnant women. For normal levels, you need at minimum 2,000 IU daily, especially in winter. A Swiss study recently demonstrated that the recommended 800 IU during pregnancy is insufficient – about 70% of pregnant women in their first trimester had deficiency, associated with gestational diabetes risk.
The body is a system – nutrient actions require adequate levels of everything else. You should ensure sufficient overall micronutrient status, for instance by taking a quality multivitamin.
Magnesium plays a key role in vitamin D metabolism, regulating it through proteins and enzymes at roughly 6–9 points, substantially affecting vitamin D function. You don't need to "load" magnesium specifically. What matters is ensuring normal magnesium status through supplements or mineral water.
Our products follow current legal limits for recommended daily intake. Across the German-speaking region, one typically can't recommend more than 800 IU daily. That's what you'll find in our multi.
Absolutely – and it's actually ideal. The 800 IU in the multi combines perfectly with our vitamin D products.
We developed a dedicated baby formula for this.
Great question. There's reason to think Europeans carry genetic variants that lower vitamin D requirements or increase conversion to active calcitriol. However: first, our levels deviate enormously from those seen in African populations – far too much. Second, it's well-established that levels below 20 ng/ml have negative physiological consequences long-term, especially for infection resistance, brain, muscle, bone, vascular system, and pancreas.
This isn't simple to answer. First, many romanticize the past. Migration from Africa to Europe created enormous selective pressures, resulting in many genetic adaptations to European life. However, not only has lifestyle fundamentally changed (and with it vitamin D turnover and needs), but diet has too. Our ancestors lived primarily near rivers and lakes – there were early settlements along the Rhine and the Alpine rivers, which once had excellent salmon populations. Salmon is among the richest vitamin D foods – 200g daily gets you through winter without deficiency. *Selective pressure refers to environmental influences strongly affecting populations, driving accumulation of certain genetic variants.
Absolutely yes. Very high vitamin D levels can calcify tissues, whether from food or skin synthesis. A classic study of Israeli lifeguards showed that the very high D levels reached in summer correlate with significantly increased kidney stone risk.
The evidence is mixed. Some studies find a clear relationship between D and T levels; others don't. Animal studies show that blocking vitamin D signaling causes hypogonadism – supported by the fact that vitamin D receptors are present in reproductive organs and tissues.
No, not at all. In normal amounts, that's very good – we need calcium and many people don't get enough from food.
Good evidence shows that vitamin D regulates serotonin production in the brain, affecting mood through at least this pathway.
Definitely. Vitamin D influences microbiome composition, modulates intestinal immunity, supports intestinal barrier integrity, and appears essential for absorbing certain micronutrients.
A few years ago, vitamin D was a "superstar" nutrient that could prevent and cure disease. Today's view is more balanced: vitamin D is tremendously important for health and preventing chronic disease. As always, every trend spawns a counter-movement that swings the opposite way. So now many discourage supplementation for various, often odd reasons. Our view: we benefit from addressing Germany's widespread deficiency in fall, winter, and spring through smart vitamin D supplementation.
It varies widely. For vitamin D, they initially focused on preventing rickets. Recent years have brought much understanding of D's effects beyond bone – thanks to animal models and mechanistic studies – which, combined with epidemiological data, has led to repeatedly updated vitamin D recommendations.
