What is Vitamin D Toxicity

Vitamin D deficiency in old age

The topics at a glance (information as of 01/2018):

For years, vitamin D has been in the shadows. In recent years, in addition to the well-known central importance in calcium and bone metabolism, a number of connections to various diseases have been uncovered. The question arises as to whether the supply of vitamin D is sufficient or whether there is a need for supplementation for certain groups.


Vitamin D is a group of different fat-soluble vitamins that are related to the regulation of the calcium balance and the mineralization of the bones (calciferols). Especially vitamins D2 (ergocalciferol) and D3 (cholecalciferol) are important for humans. Strictly speaking, both are not vitamins, but rather precursors of hormones.

On the one hand, vitamin D is supplied through food. On the other hand, vitamin D is formed from a precursor found in the skin (7-dehydrocholesterol) under the action of the sun's UV-B rays. Vitamin D production is greatest when the UV-B rays hit the skin directly. On a beautiful sunny day, up to 20,000 IU of vitamin D can be produced (40 IU correspond to 1 microgram (µg) of vitamin D3). Everything that slips between the bright sky and the skin (clouds, shadows, windows, sunscreen, clothing) can reduce vitamin D production.

Vitamin D is converted into the biologically active form (1,25-dihydroxyvitamin-D3 = calcitriol) in several conversion steps in the liver and kidneys. This form of storage (half-life around 19 days) helps to balance out the large fluctuations in vitamin D production in the presence or absence of sunlight.



The German Society for Nutrition (DGE) has so far recommended an intake of at least 10 µg vitamin D (= 400 IU) per day for seniors, this being a maintenance dose. However, this amount is not enough to compensate for an existing deficiency situation, especially in older people. The therapeutic intake is between 400 and 2,000 IU.
Since December 2011, new reference values ​​for vitamin D have been published due to a reassessment of the scientific data on vitamin D supply. Accordingly, the DGE has redefined the estimated value for adequate vitamin D intake in the absence of endogenous synthesis for the elderly at 20 µg.

Some high-fat foods contribute to the vitamin D supply, such as herring, mackerel, salmon, tuna, redfish, liver, egg yolk, butter, cream and fortified margarine, as well as mushrooms, porcini mushrooms and chanterelles. Up to 20 percent of the daily requirement can be covered with food.


Vitamin D status

Cholecalciferol is supplied to the body from food and the sun. First, it is converted to 25-hydroxy-vitamin D (25-OH-D), which circulates in the body. In a second step, if required, this is converted into the active, hormonally effective form 1,25 dihydroxy vitamin D3 (calcitriol). This level fluctuates strongly and hardly allows any conclusions to be drawn about the supply of vitamin D. A blood test therefore usually determines the value for 25-OH-D in the serum.
The laboratory results can be given in different units. It is therefore always important to ensure that the results are given in nanograms per milliliter (ng / ml) or in micrograms per liter (µg / l) or in nanomoles per liter (nmol / l).
The laboratory results show whether the supply status has to be described as sufficient (adequate), inadequate (suboptimal) or as inadequate.
Many laboratories describe values ​​below 20 ng / ml as a slight vitamin D deficiency and values ​​below 12 ng / ml as severe deficiency.
However, this assessment is often considered outdated. In recent years, many scientific studies have shown that values ​​of at least 30 ng / ml must be achieved in order to avoid various health risks, some even set the lower limit of an optimal supply at 40 ng / ml. According to the most frequently represented expert opinion recently, values ​​in the range between 40 and 80 ng / ml should be described as optimal.
Bone experts demand that the vitamin D level in the blood should be at least 30 ng / ml, especially in people over the age of 60.


Meaning of vitamin D.

Together with calcium, vitamin D has a decisive influence on bone metabolism. It

  • increases the absorption of calcium from the intestines into the bloodstream
  • reduces the excretion of calcium via the kidneys
  • increases the formation, maturation and activity of bone cells
  • activates the osteoclasts and thus keeps the extracellular calcium level in the normal range and increases the incorporation of calcium into the bones (mineralization).

Vitamin D deficiency leads to an increasing number of hip joint and femoral neck fractures, especially in women over the age of 60.
An insufficient supply leads to a mineralization disorder of the bones, insufficient calcium is incorporated, the bone mass is reduced.
According to a new study, the lack of vitamin D also means that mineralized bone tissue that surrounds the bones cannot develop a protective effect. The bone ages prematurely and becomes less resistant to fractures.
According to this, a lack of vitamin D not only reduces bone density, but also affects the quality of the bones.

In addition, vitamin D also has a beneficial effect on the muscles. It occupies receptors in muscle cells, which, through biochemical processes in the contraction of muscle fibers, helps reduce the risk of falls in the elderly.

Other advantages of an adequate supply of vitamin D include:

  • Increase in muscle mass
  • Reducing the risk of falling
  • Improve coordination
  • Lowering systolic blood pressure and improving heart failure
  • Lowering the risk of breast and colon cancer
  • Effects on sugar and fat metabolism (high vitamin D levels reduce the risk of diabetes)
  • anti-inflammatory effect, especially in immunological and allergic diseases (the susceptibility to infections of the upper respiratory tract is increased in the deficiency, in allergic diseases vitamin D increases the production of anti-allergic and anti-inflammatory messenger substances of the immune cells).

According to a British study, an undersupply of vitamin D is also often associated with a pathological decline in brain performance in old age. In addition, older people with a vitamin D deficiency are more likely to suffer from cognitive impairment, anxiety and depression.

With regard to the data on the fracture-reducing effects of calcium and / or vitamin D, the following can be said:

  • The combined administration of vitamin D and calcium leads to a reduction in femoral neck fractures in women in old people's and nursing homes with a calcium and vitamin D deficiency (effect assured)
  • The combined administration of vitamin D and calcium leads to a reduction in peripheral and vertebral body fractures in women and men of older age with calcium and vitamin D deficiency (effect likely).

In adults, the vitamin D deficiency disease is known as osteomalacia. Mixed pictures of osteomalacia (softening of the bones with skeletal deformation) and osteoporosis (bone loss) are often observed in older people.

Many studies have shown that an increase in the vitamin D level, for example through supplements (food supplements), often leads to an improvement in the above-mentioned factors. The positive effect is an increase in functionality in older people and thus a better option for the course of illnesses and possibly shorter stays in hospitals. Older people in particular who suffer from malnutrition are also more likely to have different diseases at the same time.

The effect of vitamin D is also dependent on a number of other nutrients which, like magnesium and vitamin K2, are of considerable importance as cofactors in the vitamin D metabolism.


Vitamin D supply in old age

Several studies have shown that the vitamin D level in large parts of the population is below the recommended value of at least 30 ng / ml and continues to decrease with age. The vitamin D supply is particularly poor in older people, especially older women. In women going through menopause (climacteric), vitamin D is often deficient after the body's hormone changes. Very low levels of vitamin D were found in particular in old people's home residents.

In the six months from the beginning of autumn to the beginning of spring, vitamin D formation in Germany is inadequate in natural ways. In the winter months, up to 80 percent of the population is undersupplied with vitamin D, although there are large differences depending on the latitude.

With increasing age, the skin's ability to synthesize vitamin D decreases. In addition, there is a limited conversion of vitamin D into the active form. Older people produce around four times less of their skin's own vitamin D. At the age of 70, the skin's capacity to synthesize vitamin D has been reduced by around 75 percent. The reason is the nature of the skin itself, but also the fact that the amount of the starting material 7-dehydrocholesterol (precursor of vitamin D) in the upper layers of the skin drastically decreases with age. While in younger years an occasional sunbathing is sufficient to cover 80 to 100 percent of the vitamin D requirement, older people can only produce a fraction of the necessary vitamin D in the skin despite frequent sun exposure (aging drastically reduces the production of provitamin D in the epidermis ).

Other factors can affect the production of vitamin D3 in the skin:

  • Melanin reduces the production of D3, which means that dark-skinned people need longer exposure to the sun in order to produce the same amount of vitamin D as a fair-skinned person
  • Sun protection creams (protection factor greater than 8) prevent the cutaneous production of vitamin D by more than 97 percent.

According to the National Consumption Study, 82 percent of men and 91 percent of women do not achieve the recommended vitamin D intake.
In many cases, there is a lower intake of foods containing vitamin D in old age. In the case of malnutrition, reduced vitamin D intake is also due to low general food consumption.

Immobility, disability and cognitive limitations often lead to reduced exposure to the sun and thus to greater vitamin D deficiency. Nursing home residents in particular, but also bedridden seniors who are cared for at home are particularly affected.

Other causes of a vitamin D deficiency include: chronic kidney failure, liver cirrhosis and post-gastrectomy condition.


Meeting needs and recommendations

Due to the important role of vitamin D in the human metabolism, determination and monitoring of the vitamin D level and supplementation with food supplements should definitely be considered, especially for risk groups such as the elderly.
However, in most cases the examination of vitamin D presupposes a justification of the medical necessity in the individual case. A blood test can also be ordered directly from laboratory doctors for around 35 EURO as a so-called individual health service (IGel) (at your own expense).

The recommended daily dose of 20 µg vitamin D for seniors cannot be achieved through a natural diet (for example, 250 g of mushrooms contain 5 µg of vitamin D, 100 g of tuna provide 5 µg, 100 g of herring even 23 µg of the vital vitamin) and if adequate sun exposure is not guaranteed, suitable dietary supplements or special vitamin D preparations should be used. In addition to over-the-counter vitamin D preparations (usually in a daily dose of 400 IU), there are higher-dose, prescription-only and very high-dose products in pharmacies. However, it should only be taken on the basis of individual values ​​and after medical advice.

With regard to the harmful effects of excessively high levels of vitamin D (toxicity), the experts do not provide any standardized information. The European Food Safety Authority (EFSA) has derived a tolerable total daily intake of 100 µg (4000 IU) for adults. The American Endocrinological Society even considers an intake of up to 250 µg vitamin D3 per day (10,000 IU) for healthy adults to be harmless.

For osteoporosis and fracture prophylaxis, the guideline of the umbrella organization for osteology (DVO) recommends the daily oral intake of 800 to 2000 IU of vitamin D3 (together with 1000 mg calcium per day if osteoporosis is present) if there is at least 30 minutes of exposure to sunlight for example Arms and face daily is not guaranteed.

While in the past the warning about the negative effects of solar radiation was in the foreground, there has recently been a rethinking and appropriate sun exposure is recognized and recommended as an important and suitable means of ensuring an adequate vitamin D supply.


Vitamin D is involved in calcium and bone metabolism, as well as in numerous other metabolic processes that are of crucial importance for keeping the organism healthy.
The supply of vitamin D in Germany is inadequate, especially among older people.
From a preventive medical point of view, large parts of the population should benefit considerably from a supplementary vitamin intake of 20 to 50 µg per day if the sun exposure and food choices are inadequate.


Further information and links


  • Amrein K (2015). Vitamin D deficiency - current diagnostics and prophylaxis in case studies. UNI-MED: Bremen
  • Bartl R (2011). Osteoporosis. Prevention diagnostic therapy. Thieme: Stuttgart
  • Busse B et al. (2013). Vitamin D Deficiency Induces Early Signs of Aging in Human Bone, Increasing the Risk of Fracture. Sci Transl Med 5: 1993ra88
  • Gröber U, Holick MF (2012). Vitamin D. The healing power of the sun vitamin. Scientific publishing company: Stuttgart
  • Solver C (2011). Undernourishment and malnutrition. Thieme: Stuttgart
  • Rabenberg M, Mensink GBM (2016). Vitamin D status in Germany. Journal of Health Monitoring 1 (2) 36-42
  • Room E, Gigout F, Stegmaier C, Reichrath J, Brenner H (2009). Vitamin D - an underrated protective shield? Saarländisches Ärzteblatt 62 (4) 17-19
  • Stangl G (2013). Vitamin D. Causes of inadequate supply and risk of disease for vascular calcification and allergies? Current Nutrition Med 38: 118-126
  • Ströhle A (2011). Vitamin D in the focus of prevention. Focus on nutrition 11 (6) 242-251
  • Ströhle A, Hahn W (2016). Vitamin D During Pregnancy - A Double Edged Sword? Focus on nutrition 16 (9-10) 278-283
  • Weimann A, Schütz T, Lochs H (2010). Illness-related malnutrition. Pabst Science: Lengerich
  • Worm N (2009). Healing power D. systemed: Lünen