Useful information about vitamin D

Stay healthy | 2019

Prof. Dr. Werner Seebauer is Dean of Studies – Association of German Preventologists, Head of Preventive Medicine Department of Institute of Transcultural Health Sciences (European University Viadrina) and Head of Preventive Medicine – NESA (The New European Surgical Academy).

Since 2000, prof. dr. Werner Seebauer worked only in preventive medicine, after ten years spent at the Frankfurt University Hospital. He is also involved in the medical professionals training for nutrition and prevention.

MediHelp International, together with LAMP Insurance, and in collaboration with NESA has created the NESAcard based on the wish to offer access to high standards medical services to patients all over Europe.

This way, MediHelp contributes to the medical science development and is actively involved in the international social responsibility advocacy. 


Recommendations summarized: About the recommended vitamin D doses previously only convincing evidence-based study results are available for the subject of bone health. On this data the Institute of Medicine recommends vitamin D doses of 400 to 800 IU per day (depending on age). The 1000 to 2000 IU per day recommended by some experts are in the therapeutically safe range during the time with insufficient sun exposure but this is not considered as necessary by all specialist institutions.

The safest way to provide adequate vitamin D doses is the sun exposure on the skin, where it is produced. For this a short time of sun exposure about half an hour to 25% of the body surface is sufficient during the summer time. In winter it is estimated that north of the 40th latitude (altitude of Rome), vitamin D production in the skin is insufficient and supplementation is recommended, because the usual diet provides only about 10% of the recommended vitamin D dose.

The newsletter describes more vitamin D topics and about the individual dose calculation.

Role of Vitamin D

Vitamin D plays a role in many functions of the organism (in the cardiovascular system, in the immune system etc.), but it is not yet confidently ascertainable which dose is recommended for a benefit and from which deficit it comes to increased diseases. Many factors play a role at the same time. Therefore, there are so many different trial results. Studies that examined genetic polymorphisms make assessments even more difficult, as risks or benefits may result at certain dosages depending on genetic conditions.

The convincing evidence for the recommendation of such supplementation doses so far exists only in the context of bone health studies. With all other connections to illnesses one cannot estimate the necessary vitamin D dose surely. For certain controlled medical therapies higher doses may well be used for a certain period. But then, as with other drug therapies, there are risks and the benefit-risk relations needs to be estimated.

Position of the National Cancer Institute (America) to Vitamin D:

  • Vitamin D is essential for the formation, growth, and repair of bones and for normal calcium absorption and immune function
  • Some studies suggest that higher intakes of vitamin D from food and/or supplements and higher levels of vitamin D in the blood are associated with reduced risks of colorectal cancer; however, the research results overall have been inconsistent
  • Whether vitamin D is associated with reduced risks of other cancers, remains unclear
  • Some recent studies indicate a risk elevation of potential colon cancer precursors (adenomatous bowel polyps) in certain genetic conditions (see information for your doctor below). These potential risks must be weighed against the benefits of calcium and vitamin D supplementation.

Taken together, the available data are not comprehensive enough to establish whether taking vitamin D can prevent cancer. The appropriate dose of vitamin D to use in such trials is still not clear. Other remaining questions include when to start taking vitamin D, and for how long, to potentially see a benefit. One connection of Vitamin D is plausibly explainable. Vitamin D has many important functions and the physiological supply of it (best with sun contact for the own production in the skin) is the secure way to reduce some illness risks. To be on the safe side, the doses of 1000 - 2000 IU per day should not be exceeded in the long term. For bone health, the IOM recommended doses of 400 to 800 IU per day may be sufficient for most people.

National Cancer Institute does not recommend vitamin D for cancer prevention; its only recommended for the bone health.

The best evidence of vitamin D exists in the context of bone health (osteomalacia and osteoporosis prevention)

Calcium and Vitamin D are necessary for healthy and strong bones (prevention of osteomalacia and osteoporosis). Many studies show that low calcium intake throughout life (beginning in Childhood) is associated with low bone mass and later with old people high fracture rates. National nutrition surveys have shown that many people have calcium deficiency as to healthy bones.

Several studies show that low vitamin D levels increase risk of fractures in older adults, and they suggest that sufficient vitamin D supplementation may reduce such fracture incidents. The evidence comes from several studies with more than 40.000 elderly people (mostly women) from a combined analysis of 12 fracture prevention trials. Researchers found that vitamin D supplements of about 800 IU per day reduced hip and non-spine fractures by about 20%, while lower intakes of about 400 IU or less failed to the prevention of any fracture.

The conclusion was to recommend the supplementation of moderate doses Vitamin D (600 – 800 IU/day) regularly, since these is safety. But to avoid extremely high single doses which could have adverse effects. Today some experts recommend 1000-2000 IU Vitamin D supplementa-tion per day during the time with insufficient sun exposure.

Note: Vitamin D supplementation alone did not reduce hip fracture by 15% or more. Vitamin D co-administe-red with calcium reduced hip fracture in institutionalised individuals but did not alter the relative risk of hip fracture by 15% or more in community-dwelling individuals. Still, more research is needed.

Note also, a balanced diet rich in calcium and a sufficient vitamin D synthesis or supplementation is only one part of an osteoporosis prevention or treatment. Throughout life at any age exercise and enough calcium in the diet is necessary to strengthen bones. But these may not be enough to stop bone loss caused by lifestyle, or some medications, or menopause. Consult your doctor to determine if you also need advanced prevention programs or an osteoporosis medication for therapy in addition to balanced diet, vitamin D- and calcium- supplementation as well exercise.

Table 1: The Recommended Calcium Intakes (in milligrams)

Age group

(in milligrams)

Infants 0 to 6 months


Infants 6 to 12 months


1 to 3 years old


4 to 8 years old


9 to 13 years old


14 to 18 years old


19 to 50 years old


51- to 70-year-old males


51- to 70-year-old females


70 years old


14 to 18 years old,


19 to 50 years old,


 * Source: Food and Nutrition Board, Institute of Medicine, National Academy of Sciences, 2010 

The main source of vitamin D is by sun exposure on the skin

The vitamin D supply results only to a small extent (about 10%) from the diet. Vitamin D is produced in the skin through direct sunlight on it. The invisible UV-B component of sunlight converts cholesterol (7-dehydrocholesterol) to vitamin D3 in the upper layers of the skin. In the liver, it is further metabolized to 25-OH-vitamin D, which most likely represents the vitamin D storage; and in the cells is transformed the needed bioactive form (1,2-dihydroxy-vitamin D3 ).

In the summer when you are exposed to the sun on about 25% of total skin surface (without sunscreen), the body can produce a dose of vitamin D ranging from 10,000 to 20,000 IU in less than one hour (the not yet bioactive form). From the food, the fish fats provide most of the vitamin D. For a similar dose, as in the skins production by the sun, you would need about 100g herring daily (with cod liver oil 6-10g per day could be enough).

Supplements of 500-1000 IU Vitamin D3 in tablets or capsules are more common today. The synthesis in the skin is much higher than possible via the common diet and the serum dose is also increased much longer than with diet or supplement source. In addition, the way of own production provides protection against overdosing. Although an overdose of Vitamin D by the food is hardly possible, about taking vitamin D supplements overdoses are very well possible.

What conditions are needed for vitamin D synthesis in the skin?

It depends on several factors, how much vitamin D the body produces in the skin via the sun. Essentially, this is determined by the time of the day and the season at our degree of latitudes (Central and Northern Europe). There are calculations that in countries north of latitude 40th (equivalent to the zonal of Rome), a sufficient amount of vitamin D cannot be synthesized from October to March.

When the sun's angle of insolation is lower than about 45 degrees in the sky (in the morning and evening in the summer and in the wintertime full-time), there is hardly any more vitamin D production. The flatter the angle of suns position is at the sky, the longer is the path of the sun's rays through the ozone layer, which absorbs part of the UV-radiation. The intensity of UV-B radiation – and so Vitamin D synthesis - changes strongly during the day; between 11am and 3pm it is the largest (100 - 95%), from about 5pm until sunset it is only 20 - 12.5%. A rough rule of thumb is that twice as much vitamin D is produced in the midday sun compared to the morning or afternoon.

Furthermore, there are other factors that influence vitamin D production in the skin:

  • it is different if you lie or stand and the sun shines on your skin (while lying the suns effect is about twice as high as standing or walking).
  • the size of the irradiated surface of the skin is always decisive
  • and every use of sun protection (clothing, shade and sunscreen) or clouds reduces production.

Calculations indicate that the use of effective sunscreens reduces vitamin D synthesis below 1%.

  • Skin type and age also influence. In fair-skinned, blond or red-haired people, vitamin D is produced faster than in dusky- or dark-skinned people with black hair.

In old age (> 65 years old), vitamin D synthesis in the skin is reduced to about 25%.

  • Certain infections can also reduce the vitamin D effect.

Many individual factors can play a role.

If people are increasingly working indoors, and the sun contact is late in the day, or if clothing largely prevents sunlight from reaching the skin, too little vitamin D production may result also in the summer (as measured by bone health studies).

How much vitamin D does it need?

The Institute of Medicine (IOM) recommends daily intakes (RDA) of vitamin D, estimated on the least necessary sun exposure:

  • For infants, the IOM could not determine a recommended dose because of insufficient data. However, the IOM estimates 400 IU per day as a dose, which should provide sufficient vitamin D.
  • For people from 1 to 70 years of age the recommended dose is 600 IU per day
  • For pregnant or lactating women, the recommended dose is also 600 IU per day
  • For people 71 years or older, the recommended dose is 800 IU per day.

If the sun contact is too low on the skin, the recommended dose of vitamin D should be provided by diet (saltwater fish, egg yolks, liver and fortified milk) plus targeted supplementation with vitamin D supplements. As it has been established for a long time in the first year of life and occasionally for older people. The IOM recommends no more than 4,000 IU per day for adults. However, sometimes doctors prescribe higher doses for people who are deficient in vitamin D.  [1 μg is equal to 40 IU ]

Remember that the daily requirement dose vitamin D, is usually provided only marginal via the diet (circa 10%); the physiological and at the same time safest way (without risk of overdose) is the own production in the skin by sun exposure. Toxicity from too much vitamin D is more likely caused by high intakes of dietary supplements – and hard to reach by high intakes of foods with vitamin D sources. Excessive sun exposure does not cause vitamin D toxicity (initially, only the non-bioactive vitamin D form will be formed, which will only be converted to the active form as needed). However, the IOM states that people should not try to increase vitamin D production by increasing their exposure to sunlight because this will also increase their risk of skin cancer .

How much sun for an adequate vitamin D synthesis in the skin?

Sun exposure to 25% of the skin surface (arms and legs) without sunscreen 3 times a week for 3 to 7 minutes showed values comparable to the intake of 400 IU vitamin D3. This usually results in levels around 60 nmol / l, which, according to some scientists, is considered too low.

For skin type 3 (mixed type), middle European (dark blond to dark hair color, barely any freckles) about the following times of sun exposure on both arms and legs (without sunscreen) are estimated for a daily required production of about 2000 IU vitamin D:

  • from April to May and also September - noon (11-15h) 20-30 minutes lying position sun exposure (standing twice as long) in the morning and in the evening 25-40 minutes lying sun contact (standing twice as long)
  • from June to August - noon (11-15) 15-20 minutes lying position sun contact (standing twice as long) in the morning and in the evening 25-40 minutes lying sun contact (standing twice as long)
  • October north of the 40th degree of latitude there is insufficient sun contact for the formation of 2000 IU of vitamin D per day

You can also measure the sunshine duration at the erythema threshold. For regular sunbathing without sunscreen, it is usually recommended only 25% of the duration that would lead to redness (erythema) of the skin. So, if you get the first redness for example after one hour of sun contact (caution the redness is usually only delayed visible), then 15 minutes of sun contact would be enough for sufficient vitamin D production.

It should be emphasized that in the summer you do not need the blazing sun. In case of prolonged stay outdoors (eg. 2-3 hours during the day) already in partial shade or in several short phases with direct sun on about 25% of skin surface (arms, legs and face together) results in sufficient vitamin D production.

Too long a radiation does not make sense, because then the vitamin D in the skin can be broken down again, and too long sun contacts - especially sunburns (marked erythema) increase the risk of skin cancer.

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