Vitamin D: Proper Dosage, Benefits, and What Affects Your Levels

Do you know the right dose of vitamin D for you? Recommendations can vary depending on several factors, including genetics, age, skin colour, overall health, the medications you take, and also the region where you live. In this article, we take a closer look at some of the variables that influence the resulting vitamin D concentration in the body, so you can more easily estimate how much vitamin D you personally need.

What will you learn in this article?

1. A vitamin D deficiency pandemic
2. Effects of vitamin D
3. Where is vitamin D found?
4. What affects your vitamin D level?
5. Vitamin D level in the blood
6. How much vitamin D per day?
7. When to take vitamin D?
8. How long to take vitamin D?
9. Vitamin D overdose
10. Conclusion
11. Key takeaways

A vitamin D deficiency pandemic

Vitamin D deficiency is very widespread worldwide, and in the European population, too, it occurs to a worrying extent. A large 2016 analysis of 14 European population studies revealed that more than 40% of Europeans are vitamin D deficient (serum 25(OH) vitamin D levels below 50 nmol/l) and 13% of Europeans have a severe deficiency (25(OH) vitamin D levels below 30 nmol/l). [1]

In 2018, the Czech National Institute of Public Health (SZÚ) published an analysis of 398 blood serum samples which examined, among other things, the body's vitamin D status (by measuring the 25(OH)D metabolite in blood serum). The results showed that as much as 68% of the population had insufficient levels (25(OH)D below 75 nmol/l), while only 32% of people had vitamin D status within the normal range (above 75 nmol/l). Unsurprisingly, the lowest levels were measured in the winter months, specifically in March. [2]

Effects of vitamin D

Vitamin D plays an absolutely key role in maintaining our health. This so-called sunshine vitamin influences cell division and differentiation, supporting optimal cell function throughout the body. It is essential for the proper functioning of the immune system and helps the body defend itself against infections more effectively. It plays a significant role in the absorption of calcium and phosphorus from food, which is crucial for maintaining strong bones and healthy teeth. An adequate vitamin D level is also closely linked to normal muscle function and has a demonstrably positive effect on our mood and mental well-being.

Conversely, its deficiency is associated with an increased risk of a whole range of diseases, including respiratory infections, cardiovascular disease, osteoporosis, neuropsychiatric disorders and autoimmune diseases (such as multiple sclerosis, type 1 diabetes, rheumatoid arthritis, psoriasis and others). [3] [4]

We describe the role of vitamin D in the body in more detail in the article "Shedding Light on Vitamin D".

Where is vitamin D found?

The primary source is sunlight, because thanks to UVB rays acting on our skin, the body can produce vitamin D on its own.

As for diet, the richest natural sources include oily sea fish (such as salmon, mackerel or sardines) and quality cod liver oil. Smaller amounts are also found in egg yolks, beef liver, and mushrooms that have been exposed to sunlight. Covering your need for vitamin D through diet alone is therefore very difficult.

What affects your vitamin D level?

As already mentioned, a number of factors influence the vitamin D level in the body. Intake recommendations can therefore vary depending on these variables.

• Genetics

Genes involved in vitamin D metabolism also affect the resulting serum vitamin D levels. Genetic variants influence how much vitamin D we need. The same dose of vitamin D will therefore produce a different response in each individual.

• Age

Older people have a reduced capacity of the skin to synthesise vitamin D. A recent study from 2020 [5] calculated that vitamin D production in the skin decreases by 13% for every decade of life from the age of 25. Older people also spend more time indoors and are less exposed to sunlight, which is the most important source of vitamin D.

• Skin colour

People with darker skin are more prone to vitamin D deficiency, due to the higher amount of melanin in their skin. Melanin is the pigment that determines skin colour and protects the skin from the sun's UV radiation. These individuals therefore need longer sun exposure to synthesise sufficient vitamin D.

• Body weight

Body weight is another variable affecting the need for vitamin D. In general, a higher proportion of body fat is associated with lower vitamin D levels. Obese people may therefore need a higher vitamin D intake to reach 25(OH)D levels similar to those of people with normal weight. [6]

People who are overweight or obese are generally at greater risk of common diseases, so vitamin D dosing should also depend on BMI, so that these individuals reach the amount of vitamin D needed to support their health. [7] The Endocrine Society recommends increasing the vitamin D dose 2 to 3 times in obese patients.

• Latitude of residence

Countries near the equator have plenty of sunlight all year round. People living further from the equator, on the other hand, get less sunlight, which also contributes to lower vitamin D levels in the body. At Central European latitudes, especially during the winter months, it is therefore important to ensure an adequate intake of vitamin D through quality supplementation.

• Certain health conditions

Vitamin D is a fat-soluble vitamin, and its absorption depends on the gut's ability to absorb fat from food. Fat malabsorption is associated with health problems such as some forms of liver disease, cystic fibrosis, coeliac disease, Crohn's disease or ulcerative colitis. Inflammatory bowel diseases also contribute to vitamin D deficiency.

• Pregnancy, breastfeeding women & infants

The vitamin D content of breast milk is closely related to the mother's vitamin D status. Breast milk alone may therefore not be enough to cover the vitamin D needs of breastfed infants. A study examining maternal vitamin D status and its effect on the vitamin D content of breast milk concluded that vitamin D deficiency is widespread during pregnancy and breastfeeding and may increase the likelihood of deficiency in breastfed infants who are not sufficiently exposed to sunlight and do not receive vitamin D supplements. [8] Studies also suggest that the breast milk of mothers who take a daily supplement containing at least 2,000 IU of vitamin D3 has higher levels of this vitamin.

It has been shown that vitamin D supplementation during pregnancy helps reduce the risk of preeclampsia by 60%, gestational diabetes by 50% and preterm birth by 40%. Prenatal screening of 25(OH)D levels to identify vitamin D deficient women, followed by appropriate measures, can therefore be an effective way to reduce these pregnancy risks. [9]

• Magnesium

It should also be mentioned that various steps in vitamin D metabolism depend on magnesium as a cofactor. When magnesium is deficient, vitamin D activation is reduced. The combined effects of magnesium and vitamin D deficiency can lead to higher health risks, such as bone fractures.

In summary, certain groups of people need more vitamin D than others. These include older adults, people with darker skin, obese individuals, people who avoid the sun in summer, people living further from the equator and, last but not least, those with certain health conditions such as liver or kidney disease, malabsorption syndromes and inflammatory bowel diseases.

Vitamin D level in the blood

How can you reliably find out whether you are vitamin D deficient? The best indicator is a blood test measuring the 25(OH)D metabolite, also known as 25-hydroxyvitamin D. The usual range considered normal is 75 to 250 nmol/l. Values below 75 nmol/l are insufficient, and anything below 50 nmol/l represents a severe deficiency. 

However, extensive research [10] focusing on immunity recommends maintaining serum vitamin D levels somewhat higher, between 100 and 150 nmol/l. Few people at Central European latitudes reach this optimal range without supplementation. If you want to know your levels, you can use a simple home self-test from a drop of blood, or take our quick orientation quiz on our website.

Maintaining vitamin D levels in the range of 100 to 150 nmol/l is also endorsed by Jakub Přibyl, author of Trime formulations and a long-time consultant in personalised nutrition. "Reference ranges for 25-hydroxyvitamin D differ between laboratories, so many people with a mild 25(OH)D deficiency may be classified by their doctor as adequate, even though by the latest criteria this is already a state of deficiency. The same applies to the vitamin D supplementation recommendations of various professional societies and health organisations. The reference intake of vitamin D from diet or supplementation ranges from 400 to 5,000 IU per day. From my own practice, I consider serum 25(OH)D values between 100 nmol/l and 150 nmol/l to be optimal, and very few people in our conditions reach them without supplementation. That is why I find it useful to know your 25(OH)D level, measured at least twice a year. For example, at the start of the 'sunny' season at the turn of April and May, and then sometime in November, when your stores of 'summer' vitamin D are already depleted. This way, everyone can get a better idea of how their vitamin D metabolism is really doing and whether intake from diet and sunlight is enough for them or not." says Jakub Přibyl.

How much vitamin D per day?

The reference intake of vitamin D differs between organisations. EFSA sets a preventive daily dose of 600 IU for adults. [11] Many experts consider this amount too low and recommend a higher intake.

There is also no consensus between organisations on the safe upper limit for vitamin D supplementation. While the Endocrine Society states an upper daily limit of 10,000 IU for adults, EFSA recommends not exceeding 4,000 IU/day. [12] [13]

The table below shows the recommended daily values and upper intake limits for vitamin D by age (according to the Endocrine Society recommendations). [4] These recommendations apply to individuals at risk of vitamin D deficiency.

It is important to remember that vitamin D3 should be taken together with vitamin K2. These two vitamins work in perfect synergy. While vitamin D3 ensures that calcium is absorbed into the blood, vitamin K2 makes sure that calcium is safely deposited in bones and teeth rather than in the walls of blood vessels.

When to take vitamin D?

Because vitamin D is fat-soluble, it is best taken with a meal that contains at least a little fat. This can be a teaspoon of quality oil, eggs, nuts or avocado. Fat is absolutely essential for the vitamin to be properly absorbed in the digestive tract. Experts generally agree that it is best to take vitamin D in the morning with breakfast or at midday with lunch.

How long to take vitamin D?

At Central European latitudes, the absolute basis is to supplement vitamin D from autumn to spring. It is usually recommended to start in September and continue until April, when the sun is low and not enough UVB radiation reaches us. However, if you spend most of the summer in an office, regularly apply sunscreen with a UV protection factor outdoors, or belong to an at-risk group such as people with excess weight, it will be beneficial for you to take vitamin D all year round. The duration and dose should ideally be set individually based on your current blood vitamin D level.

Vitamin D overdose

Vitamin D is fat-soluble and can accumulate in the body. However, adverse effects are rare. They usually appear only after long-term use of extremely high doses, in the order of tens of thousands of IU per day over several months. The typical sign is elevated calcium levels in the blood (hypercalcaemia). This manifests as severe nausea, muscle weakness, kidney stone formation and, in extreme cases, organ damage. When recommended doses are followed, however, supplementation is completely safe.

Conclusion

Sufficient vitamin D is key to maintaining our overall health, yet most of the population is deficient. Appropriate vitamin D intake recommendations depend on individual health status, body weight, the latitude where we live, and dietary and cultural habits. At Central European latitudes, sun exposure and dietary vitamin D intake alone are not enough to maintain the desired vitamin D concentration all year round. For this reason, supplementation is often necessary to achieve optimal vitamin D status. Adverse effects related to vitamin D use, such as hypercalcaemia, are rare and usually result from long-term use of extremely high doses exceeding tens of thousands of IU per day.

Vitamin D3 + K2, 1000 IU D3 / 25μg K2-MK7

Key takeaways

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