The occurrence of vitamin D3 in nature is very limited. Cow’s milk and breast milk contain less than 5 I.U. (International Units) per 100 ml. However, in addition to vitamin D3, active vitamin D metabolites are also present in very low concentrations.

Fish liver contains very high amounts of vitamin D3 (cod liver oil). The following overview gives a selection of foods that contain appreciable amounts of vitamin D3 (vitamin D3 content in µg per 100 g).

Eel                                90

Herring                        30

Meat                         < 10

Cheese                     < 1

Dairy products         < 1

However, vitamin D3 holds a special position among the vitamins, as it is both supplied through the diet and formed by humans themselves through UVB light exposure (sunlight). The intake via the diet with the usual foods is often not sufficient to ensure a desired supply of vitamin D3. Only frequent sun exposure can achieve the desired supply without taking a vitamin D product. However, vitamin D synthesis in the skin is determined by geographical, climatic and cultural factors. These include, for example, latitude, season, time of day, sunshine duration and clothing, as well as the length of time spent outdoors. Other influencing factors include the use of sunscreens, the pigmentation of the skin and the thickness of the skin, which decreases with age.

In the summer months, however, it is possible to achieve the desired vitamin D intake through endogenous synthesis. In Germany, however, the UVB index falls below 3 for about 6 months of the year and thus sufficient vitamin D synthesis is not guaranteed. 

The contribution of endogenous synthesis of vitamin D3 supply by UVB light exposure when spending time outdoors needs to be investigated in more detail in the future. On the one hand, UVB exposure is necessary for vitamin D synthesis; on the other hand, UV exposure increases the risk of skin cancer, especially in our modern times. In addition, the increased use of sunscreens has been advised for some years. However, it should be noted here that the use of day creams with a sun protection factor and the use of sunscreens significantly reduce vitamin D synthesis in the skin.

However, a lack of vitamin D supply can cause health problems for humans. These possible risks are described in detail in the literature. Therefore, especially for older people (older than 60), a balanced supply of vitamin D3 is also recommended in the winter half-year via appropriate dietary supplements or via medicines.

The German Society for Nutrition recommends 20 µg vitamin D3/tgl for children from 1 year of age, adults, pregnant and breastfeeding women with a lack of endogenous synthesis.

The European Food Safety Authority (EFSA) already established the following Tolerable Upper Intake Levels for vitamin D3 in 2012.

2) Vitamin D in Food:

3 ) Vitamin D supply in Germany:

The largest amount of vitamin D is taken in through fish (approx. 33 %) and fish products (approx. 15 %). About 10 % each of the vitamin D intake comes from fats, eggs and milk/cheese (Max Rubner Institute 2008).

In the study “Ernährung ab 65” (Stehle et al. 2000), 3-day dietary protocols of the 583 male participants showed a median vitamin D intake of 3.6 μg per day (P5 – P95 1.0 – 10.6 μg per day), the median vitamin D intake of the 789 female participants was 2.9 μg per day (P5 – P95 0.8 – 8.2 μg/day). 84% of men and 91% of women did not reach the recommended intake of 10 μg per day, 61 and 71% respectively consumed less than half of the recommended amount.

In children and adolescents, the median intake is even lower: according to the EsKiMo study (nutrition module of the KiGGS study), 6- to 11-year-old boys consume 1.4 μg and girls of the same age 1.3 μg of vitamin D per day. Boys aged 12 to 17 have a median vitamin D intake of 2.2 μg and girls in this age group have an intake of 1.7 μg vitamin D per day (Mensink et al. 2009).

Consequently, the median vitamin D intake of 65-80 year old seniors reaches only about a quarter of the recommendation. However, adolescents and young adults aged 14-24 are also conspicuous for their low median vitamin D intake compared to the reference values. A total of 82 % of men and 91 % of women do not reach the recommended daily vitamin D intake. The proportions are highest among adolescents and young adults (>86 % for men, >96 % for women) and seniors (94 % for men and 97 % for women).

The situation also worsens in the northern hemisphere during the winter months. This is confirmed by numerous researchers and nutritionists. Prof. Dr. Zittermann deals with this in particular in his paper “The estimated benefits of vitamin D for Germany”. The body’s own vitamin D synthesis comes to an almost complete standstill during the winter months.

The first signs of a vitamin D 3 deficiency can be associated with an increased susceptibility to infections, especially in the winter months.

4) On the safety of vitamin D3:

As early as 2002, the Scientific Committee on Food (SCF) defined a Tolerable Upper Intake Level (UL value) of vitamin D as follows:

Summery of upper levels for vitamin D:

⁺This value also applies to pregnant and breastfeeding women.

The “Reference Values for Nutrient Intake 2008” already state: “A daily vitamin D intake of up to 50 µg can be considered safe for adults”.

Current levels:

Based on today’s findings, the European Food Safety Authorities (EFSA) already set new Tolerable Upper Intake Levels for vitamin D in July 2012:

In addition, as a safe upper intake limit, the Institute of Medicine (IOM) doubled the dose from 2000 units to 4000 units per day for adults and set it at 1000 – 3000 units per day for children depending on age in its latest vitamin D recommendations.

In this regard, the summary statement reads:

The majority of the working group members come to the following conclusion: For older people (≥ 65 years), a daily intake of at least 800 IU (20 μg) of vitamin D should be recommended

• as this dose has been shown in intervention studies to reduce the risk of musculoskeletal dysfunction, falls, fractures, and premature death with convincing or probable evidence,
• as this dose has been shown in intervention studies to reduce the risk of musculoskeletal dysfunction, falls, fractures, and premature death with convincing or probable evidence
• and no significant risks or side effects are expected at this dose.                               

¹ 1 µg = 40 International Units (IU); 1 IU = 0.025 µg

Daily or weekly intake?

However, these amounts can also be consumed in higher dosages, as numerous studies show, 1x weekly or in even higher dosages 1x monthly.

Instead of daily supplementation with vitamin D, the dosage for the whole week or month can also be consumed once a week or once a month.

4. Safe upper limits of vitamin D3:

Intoxications could not be proven even with daily intakes of up to 100 μg. However, at intakes of more than 100 μg per day, an increase of the calcium concentration in the plasma may occur in isolated cases despite an increased excretion of calcium in the urine.

Tolerable upper limit of intake

In infants, daily amounts of more than 25 μg of vitamin D must not be given without a targeted indication and regular monitoring of the calcium concentration in the plasma and calcium excretion via the urine. The EFSA assesses a daily vitamin D intake of up to 50 μg for adults as safe. The US Institute of Medicine has set the tolerable upper limit for daily vitamin D intake at 100 μg.

According to the work of Hathcock, toxic effects are to be expected with daily intakes of > 250 µg. Therefore, the American Society of Endocrinology also set the daily upper limit for the intake of vitamin D in summer 2011 with a UL value (Upper Safe Limit) for adults of 10,000 I.U. per day, corresponding to 250 µg (DAZ 2011, No. 29, p. 67).

The dietary regulation also allows a vitamin D intake of up to 2.5 or 3.0 µg/100 kcal/day in Appendix 6. With an average calorie intake of  2000 kcal, this corresponds to a value of 50-60 µg vitamin D.

5. Summary assessment of the marketability of vitamin D

Numerous studies show that an adequate vitamin D supply can be provided by a lower daily dosage or in a higher dosage 1x weekly or even 1x monthly.

Physiologically, there are no significant differences.

As early as 2012, the EFSA specified a Tolerable Upper Intake Level (UL value) of 100 µg/day for vitamin D3, i.e. a total daily intake at this level is still considered safe from a nutritional-physiological point of view.

The current intake recommendations in the DACH reference values are stated as 20 µg/day corresponding to 800 I.U.

6. Assured statements on vitamin D3:

The substantiated statements on vitamin D3 are listed in Regulation No. 432/2012/EU:

• Vitamin D contributes to a normal absorption/utilisation of calcium and phosphorus.

• Vitamin D contributes to normal blood calcium levels.

• Vitamin D contributes to the maintenance of normal bones.

• Vitamin D contributes to the maintenance of normal muscle function.

• Vitamin D contributes to the maintenance of normal teeth.

• Vitamin D contributes to normal immune system function.

• Vitamin D has a function in cell division.