Vitamin D deficiency – under-supplied despite sunlight?

from Mag. Kristiina Singer, MSc
on 17.04.2024
Man with vitamin D deficiency Man with vitamin D deficiency

Sun rays that tickle our noses don’t just make our hearts sing. They also penetrate deep under the skin and provide us with a very special vital substance – the fat-soluble vitamin D. Vitamin D, however, is not a vitamin in the real sense. In fact, it’s the precursor of a hormone and the only vitamin we can make ourselves in sunlight. For a long time, the “sun vitamin” was mainly associated with healthy bones. However, the scientific findings of the last two decades have attributed vitamin D with an important preventive role in the health of the entire organism. This is also reflected in the structure of the body, which has “docking sites” for sun vitamins in more than 35 tissues.

The causes of vitamin D deficiency: How vitamin D deficiency develops

Vitamin D has a special position among vitamins, because its main requirement is not covered by the diet as in most cases, but it is produced independently by our body. All it needs is the cholesterol precursor “7-dehydro-cholesterol” and strong enough sun exposure on the skin. But it often fails with the latter. Our modern lifestyles, which mainly take place indoors, can stand in the way of a sufficient supply of vitamin D. For this reason, experts recommend, for example, that students or "office workers" use the lunch break to go outside for at least 15 minutes on as many sunny days as possible (without sun protection + uncovered face, neck and hands). However, fresh air does not guarantee sufficient vitamin D formation.

Vitamin D deficiency despite sunlight

80-90% of the vitamin D requirement can be met by the body itself using sunlight – so much for the theory. However, in practice, a number of factors get in the way of sufficient vitamin D formation. These include cold weather, advanced age, a dark skin type or the use of high sun protection factors. In the past, it was thought that the body’s own production was almost completely switched off by skin creams, make-up or sun cream with a sun protection factor of over 8. More recent data shows that when using sunscreens with moderate sun protection factors of up to 20, sufficient vitamin D formation takes place, but with very high sun protection factors over 20, as is highly recommended for children or during the summer holidays in bright sunlight, a restriction in vitamin D formation can be assumed. 

In addition, the body’s own production is dependent on where the sun is or the angle of the sun’s rays. Sunlight is strong enough only if the UV-B index reaches a value of more than 3, which corresponds to UV-B radiation of 290–315 nm. A simple rule of thumb to assess whether the intensity of solar radiation is sufficient for intrinsic vitamin D synthesis is to compare your shadow with your body length: If your shadow is longer than you are tall, the radiation intensity is too low. Accordingly, the body’s own vitamin D synthesis in our latitudes stops almost completely from October to March and even in the morning and evening hours, the sun’s radiation is not sufficient.

Vulnerable vitamin D synthesis – possible hazards at a glance:

  • Insufficient angle or intensity of the sun
  • Cold weather
  • Very overcast
  • Window panes
  • Covered skin
  • Sunscreen with a high sun protection factor (>20)
  • Dark complexion
  • Advanced age
  • Kidney disease
  • Digestive disorders

Mission Impossible – Needs coverage via the diet

In addition to the body's own production, vitamin D can also be absorbed via food – however, the D-A-CH companies for nutrition agree that it is virtually impossible to meet the body’s needs purely through a standard diet. This is also recorded in the Austrian nutrition report. Liver and fatty fish, such as salmon, sardines, eel and herring, contain significant concentrations of vitamin D, but do not feature in the diet on a daily basis or in great quantities. More popular sources of vitamin D, such as egg yolks, milk and dairy products, on the other hand, have only very limited amounts of vitamin D and are therefore unable to meet the daily needs. Especially in the case of low or no production (e.g. in the winter months, during full-time work indoors), it is not possible to achieve the desired reference value of at least 800 IU (international units) from nutrition alone.

Vitamin D3 drops

Vitamin D3 as practical drops making them even easier to take

Vitamin D3 - also now available to take as drops: Our vitamin D3, proven for many years, is now available in a practical liquid form, making them even easier to take. As a single drop already contains the recommended daily dosage of 25 µg (= 1000 I.U.), taking multiple drops is a thing of the past. Thanks to their sunflower oil content, Biogena Vitamin D3 Tropfen have a pleasantly neutral taste and do not contain medium-chain triglycerides from palm oil.

vitamin D3 drops
Vitamin D3 Tropfen

Vitamin D deficiency symptoms and consequences

Vitamin D is good for bones. This is well-known. Less well-known are the countless scientific findings of the last two decades, which ascribe vitamin D with an important preventive role in maintaining the health of the entire organism. This is also reflected in the structure of the body. For example, more than 35 tissues in our body have “docking sites” for the sun vitamin. Accordingly, the potential symptoms and vitamin D deficiency consequences are also far reaching.

What are symptoms for vitamin D deficiency? What can vitamin D deficiency cause?

  • Head & nerves: irritability, restlessness, migraine, ringing in the ears
  • Hair: hair loss
  • Immune system: susceptibility to infection, autoimmune reactions, increased risk of cancer
  • Muscles: muscle weakness, muscle pain, limb pain, muscle cramps
  • Bones: Impaired bone mineralisation (children: rickets, adults: osteomalacia), calcium deficiency, bone pain and deformations, bone fractures
  • Metabolism: Increased risk of diabetes, increased risk of high blood pressure
More about vitamin D and muscle and bones

The winter season - a "heyday" for infections.

Colds and flu-like infections peak in the autumn and winter. Doctors and researchers have suspected for some time that this annual “disease tsunami” is aided and abetted by a reduced vitamin D level. This is not least because vitamin D activates both antiviral and antibacterial proteins and also influences further immune processes. A vitamin D deficiency, however, can seriously impact the performance of the immune system. There is also a lot to support a link between vitamin D and respiratory diseases – and more studies are being conducted into this. Among other things, an Austrian study was able to reveal a connection between the frequency of infections and illnesses of employees and their poor or sub-optimal vitamin D supply.  

Risk target group for vitamin D deficiency

The Robert Koch Institute estimates that over 57% of adults have poor levels of vitamin D in their blood. The situation is even more precarious with the elderly population. Many elderly people are outdoors less for health reasons or due to reduced mobility. In addition, as we age, the skin becomes thinner and as a result the ability to produce vitamin D in the body deteriorates greatly.

Other risk groups for vitamin D deficiency are women when pregnant and breastfeeding, people with a darker skin type, growing children, girls and women who mask themselves for cultural or religious reasons, people who work full-time indoors or in shift operations, or infants or small children who have to be protected from direct sunlight in the first years of life.

Overview: Risk groups for vitamin D deficiency

  • People with low or no sun exposure
  • Shift workers
  • Older people
  • Infants and toddlers
  • Pregnant and breastfeeding women
  • People who always wear long clothing
  • Dark-skinned people
  • Smokers

Vitamin D deficiency in children

The child’s body is growing and constantly changing. It is therefore all the more important to supply adolescents with sufficient micronutrients. As a regulator of calcium and phosphate metabolism, vitamin D has a crucial effect on bone firmness. In the case of a deficiency, the bones are not able to integrate minerals into the bone substance. As a result, the bones remain soft and deform. In such cases, doctors talk about rickets.

In order to keep the risk of rickets at bay, a possible vitamin D deficiency should be averted in babies: Breast milk contains too little vitamin D – and the content of bottled food is also not sufficient. At the same time, a baby’s sensitive skin should not be exposed directly to sunlight. For this reason, it is recommended for babies to take preventative vitamin D (400 – 500 IU). According to the German Society for Paediatric and Adolescent Medicine (DGKJ), this recommendation applies until the child’s second early summer.   

But what about older children? In these cases, vitamin D supply is anything but optimal – and this is at a stage of development that is important for bone development and growth. For example, an investigation by the German Robert Koch Institute (KiGGS study) found that 62% of boys and 64% of girls between the ages of 3 and 17 had a reduced vitamin D level (< 50 nmol/l) in the blood.

Vitamin D deficiency symptoms in children

Although due to the recommended administration of vitamin D (from the first week of life to the second early summer) rickets rarely occurs, other signs of vitamin D deficiency are less specific. The following symptoms may indicate a child vitamin D deficiency:

  • Susceptibility to infections
  • Pronounced fatigue
  • Poor performance
  • Restlessness
  • Sleep disorders
  • Increased sweating
  • Tooth enamel defects, caries
Junior Vitamin D3
Vitamin D drops for children to support healthy growth, healthy bone development and the normal function of the immune system
Junior Vitamin D drops for children and babies in liquid form
Junior Vitamin D3 Tropfen

Measure & diagnose vitamin D deficiency

Vitamin D is the only vitamin that is supplied primarily through the sun rather than through the diet. And yet, studies have repeatedly shown that many Europeans have inadequate vitamin D supplies. Many people are probably wondering what their own vitamin D supply is like.

How can you determine a vitamin D deficiency?

A vitamin D test can easily throw light on the problem. To determine vitamin D status, vitamin D is measured as 25 hydroxy vitamin D3 in the blood and, depending on the laboratory, either indicated as nmol/l or as ng/ml*. (Conversion from nmol/l to ng/ml: simply divide the value in nmol/l by 2.5.)

Values – from which point should you be worrying about a vitamin D deficiency?

Evaluation of the status

25 hydroxy vitamin D serum level (nmol/l))

25 hydroxy vitamin D serum level (ng/ml) (-> equivalent to "μgl/l")

serious deficiency

< 50 nmol/L

< 20 ng/ml

slight deficiency

50 - 75 nmol/L

20 - 30 ng/ml

Sufficient supply

75 - 100 nmol/L

30 - 40 ng/ml

Optimum supply

100 - 150 nmol/L

40 - 60 ng/ml

Table: Assessment of vitamin D status

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