Vitamin D: Most people ingest it in vain. Are you one of them?
Vitamin D: Most people ingest it in vain. Are you one of them?
Hardly any supplement is swallowed as often. However, large-scale studies present a sobering picture, clearly separating those of you who are genuinely at risk from the clever marketing.
Hardly any supplement is swallowed as often. However, large-scale studies present a sobering picture, clearly separating those of you who are genuinely at risk from the clever marketing.
Vitamin D is the best-selling food supplement in the German-speaking world. It is claimed to strengthen bones, ward off infections, prevent cancer and improve mood. According to surveys, up to two-thirds of the population in Austria have suboptimal levels during the winter months because the geographical location from October to April barely allows any endogenous synthesis via the skin.
This sounds like a clear case for a daily capsule. However, when researchers tested these significant promises in randomised controlled trials, surprisingly little of them held up. The honest answer to the question of whether vitamin D supplementation is appropriate is: it depends on who you are. And indeed, dramatically so.
What the large studies really show
The most significant study to date is the US VITAL study involving around 25,000 participants. Published in the New England Journal of Medicine in 2022, the findings showed that 2,000 International Units of vitamin D daily did not reduce the number of bone fractures in generally healthy adults, neither overall nor at the hip. [1] Prior to this, the same study had already demonstrated that the supplements had no measurable effect on cancer, cardiovascular disease, or overall mortality.
And this is not just an isolated study. The independent US Preventive Services Task Force (USPSTF) reached the same conclusion after reviewing the evidence: there is no robust benefit for preventing fractures in healthy, community-dwelling adults. [2] A large Cochrane review also found no convincing effect on mortality in the general population. [3]
Why the deficiency alarm is still justified
This is where many headlines get it wrong. "No benefit for healthy people" is completely different from "vitamin D is useless". The major studies mostly recruited people who already had adequate vitamin D levels. If you don't have a deficiency, you simply won't benefit from topping up your levels even further.
However, if you have a true deficiency, it is a completely different story. A severe vitamin D deficiency leads to rickets in children and osteomalacia (a painful softening of the bones) in adults. These conditions are very real, and supplementation reliably prevents them. So, the debate isn't about whether we need it, but rather who needs it.
These groups really should supplement
There are clearly defined risk groups for whom taking vitamin D is medically sensible and firmly established in guidelines:
Infants in their first year of life. Supplementation is standard practice in Austria to prevent rickets.
Older people in care homes who rarely get outdoors.
People with darker skin living in northern latitudes, as more melanin slows down your body's own vitamin D production.
People who cover their skin or rarely leave the house.
People with medical conditions that affect absorption, such as coeliac disease or inflammatory bowel disease, as well as those who have had certain gastrointestinal surgeries.
For everyone else, the federal public health portal explicitly does not recommend vitamin D supplements for general disease prevention in healthy adults without risk factors. [4]
How much is sensible, and when does it become too much?
The Austrian Nutrition Society suggests a guideline value of 800 International Units (20 micrograms) per day for adults, while the European Food Safety Authority sets the daily intake at 600 units. [5] The tolerable upper limit for long-term daily intake is 4,000 units.
Remember, more is not always better! Very high doses can cause calcium levels in your body to rise to dangerous levels, potentially leading to kidney stones, nausea, and in extreme cases, heart rhythm issues. High-dose monthly or annual injections, which used to be popular, are now generally advised against because some studies actually showed an increased rate of falls.
What the large studies really show
The most significant study to date is the US VITAL study involving around 25,000 participants. Published in the New England Journal of Medicine in 2022, the findings showed that 2,000 International Units of vitamin D daily did not reduce the number of bone fractures in generally healthy adults, neither overall nor at the hip. [1] Prior to this, the same study had already demonstrated that the supplements had no measurable effect on cancer, cardiovascular disease, or overall mortality.
And this is not just an isolated study. The independent US Preventive Services Task Force (USPSTF) reached the same conclusion after reviewing the evidence: there is no robust benefit for preventing fractures in healthy, community-dwelling adults. [2] A large Cochrane review also found no convincing effect on mortality in the general population. [3]
Why the deficiency alarm is still justified
This is where many headlines get it wrong. "No benefit for healthy people" is completely different from "vitamin D is useless". The major studies mostly recruited people who already had adequate vitamin D levels. If you don't have a deficiency, you simply won't benefit from topping up your levels even further.
However, if you have a true deficiency, it is a completely different story. A severe vitamin D deficiency leads to rickets in children and osteomalacia (a painful softening of the bones) in adults. These conditions are very real, and supplementation reliably prevents them. So, the debate isn't about whether we need it, but rather who needs it.
These groups really should supplement
There are clearly defined risk groups for whom taking vitamin D is medically sensible and firmly established in guidelines:
Infants in their first year of life. Supplementation is standard practice in Austria to prevent rickets.
Older people in care homes who rarely get outdoors.
People with darker skin living in northern latitudes, as more melanin slows down your body's own vitamin D production.
People who cover their skin or rarely leave the house.
People with medical conditions that affect absorption, such as coeliac disease or inflammatory bowel disease, as well as those who have had certain gastrointestinal surgeries.
For everyone else, the federal public health portal explicitly does not recommend vitamin D supplements for general disease prevention in healthy adults without risk factors. [4]
How much is sensible, and when does it become too much?
The Austrian Nutrition Society suggests a guideline value of 800 International Units (20 micrograms) per day for adults, while the European Food Safety Authority sets the daily intake at 600 units. [5] The tolerable upper limit for long-term daily intake is 4,000 units.
Remember, more is not always better! Very high doses can cause calcium levels in your body to rise to dangerous levels, potentially leading to kidney stones, nausea, and in extreme cases, heart rhythm issues. High-dose monthly or annual injections, which used to be popular, are now generally advised against because some studies actually showed an increased rate of falls.
"No benefit for healthy people doesn't mean it's useless!"
"No benefit for healthy people doesn't mean it's useless!"
"No benefit for healthy people doesn't mean it's useless!"
What does this mean for you?
Do not swallow anything on suspicion, but do not stop taking anything abruptly either. The sensible approach consists of three steps.
Assess yourself honestly. Do you belong to one of the risk groups mentioned above?
A general blood test for everyone is not necessary, but it is useful in the case of symptoms, risk factors, or uncertainty. This allows an actual deficiency to be corrected in a targeted manner instead of dosing in the dark.
If you supplement, stay within a moderate range, usually 800 to 2,000 units daily, instead of high bolus doses.
Exactly these kinds of questions are what we clarify at the PVZ Primary Care Centre in Vienna's Josefstadt, for instance, during a preventive health examination. We look at your individual situation instead of a trend and decide together whether a test or a preparation really makes a difference for you. Appointments are available under Appointment and Contact.
Frequently Asked Questions
Are vitamin D supplements useful for healthy people?
For healthy adults without deficiency and without risk factors, large studies such as VITAL show no resilient benefit in bone fractures, cancer, or mortality. Supplementation is primarily useful in the case of a proven deficiency or in defined risk groups.
Who in Austria is at an increased risk of vitamin D deficiency?
Particularly affected are infants, elderly individuals with little sun exposure, people with dark skin, individuals who cover their skin or rarely go outdoors, as well as persons with intestinal malabsorption. Furthermore, during the winter months, a large part of the population has lower levels.
How much vitamin D per day is recommended?
As a guideline, 600 to 800 International Units, or 15 to 20 micrograms daily for adults, are recommended. The tolerable upper intake level for long-term consumption is 4,000 units per day.
Can you overdose on vitamin D?
Yes. Long-term very high doses can dangerously increase blood calcium levels, leading to kidney stones, nausea, and in severe cases, cardiac arrhythmias. Without medical consultation, you should not permanently dose above the upper limit.
Should I have my vitamin D levels measured?
A test for everyone is not necessary. It is useful if you have symptoms, belong to a risk group, or if a targeted treatment decision is pending. It is best to bring this up during a preventive health examination.
Sources
LeBoff MS et al. Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults (VITAL). New England Journal of Medicine, 2022.
US Preventive Services Task Force. Vitamin D, Calcium, or Combined Supplementation for the Primary Prevention of Fractures. JAMA, 2018.
Bjelakovic G et al. Vitamin D supplementation for prevention of mortality in adults. Cochrane Database of Systematic Reviews, 2014.
Gesundheit.gv.at. Vitamin D: Bedarf, Quellen und Mangel. Public Health Portal of Austria, 2024.
EFSA. Dietary reference values for vitamin D. EFSA Journal, 2016.
This article is for general information purposes and does not replace individual medical advice. For health-related questions, please consult your doctor, gladly at our PVZ.
What does this mean for you?
Do not swallow anything on suspicion, but do not stop taking anything abruptly either. The sensible approach consists of three steps.
Assess yourself honestly. Do you belong to one of the risk groups mentioned above?
A general blood test for everyone is not necessary, but it is useful in the case of symptoms, risk factors, or uncertainty. This allows an actual deficiency to be corrected in a targeted manner instead of dosing in the dark.
If you supplement, stay within a moderate range, usually 800 to 2,000 units daily, instead of high bolus doses.
Exactly these kinds of questions are what we clarify at the PVZ Primary Care Centre in Vienna's Josefstadt, for instance, during a preventive health examination. We look at your individual situation instead of a trend and decide together whether a test or a preparation really makes a difference for you. Appointments are available under Appointment and Contact.
Frequently Asked Questions
Are vitamin D supplements useful for healthy people?
For healthy adults without deficiency and without risk factors, large studies such as VITAL show no resilient benefit in bone fractures, cancer, or mortality. Supplementation is primarily useful in the case of a proven deficiency or in defined risk groups.
Who in Austria is at an increased risk of vitamin D deficiency?
Particularly affected are infants, elderly individuals with little sun exposure, people with dark skin, individuals who cover their skin or rarely go outdoors, as well as persons with intestinal malabsorption. Furthermore, during the winter months, a large part of the population has lower levels.
How much vitamin D per day is recommended?
As a guideline, 600 to 800 International Units, or 15 to 20 micrograms daily for adults, are recommended. The tolerable upper intake level for long-term consumption is 4,000 units per day.
Can you overdose on vitamin D?
Yes. Long-term very high doses can dangerously increase blood calcium levels, leading to kidney stones, nausea, and in severe cases, cardiac arrhythmias. Without medical consultation, you should not permanently dose above the upper limit.
Should I have my vitamin D levels measured?
A test for everyone is not necessary. It is useful if you have symptoms, belong to a risk group, or if a targeted treatment decision is pending. It is best to bring this up during a preventive health examination.
Sources
LeBoff MS et al. Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults (VITAL). New England Journal of Medicine, 2022.
US Preventive Services Task Force. Vitamin D, Calcium, or Combined Supplementation for the Primary Prevention of Fractures. JAMA, 2018.
Bjelakovic G et al. Vitamin D supplementation for prevention of mortality in adults. Cochrane Database of Systematic Reviews, 2014.
Gesundheit.gv.at. Vitamin D: Bedarf, Quellen und Mangel. Public Health Portal of Austria, 2024.
EFSA. Dietary reference values for vitamin D. EFSA Journal, 2016.
This article is for general information purposes and does not replace individual medical advice. For health-related questions, please consult your doctor, gladly at our PVZ.
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If you enjoyed this article, then you probably feel exactly the same way we do: the urge to take action and really make a difference. But why should you stop at just reading? Join us and become part of what we are building here.
