The controversy around Vitamin D – Do we need to supplement beyond infancy?
Vitamin D is a key component for the growth and development of children and adolescents, influencing a multitude of functions. In Germany as well as in many other countries worldwide it has been recognized that there is a need for a higher vitamin D intake in all age groups, from infancy to older ages (Cashman et al. 2016, Kunz et al. 2018, Zittermann 2018).
To reach a sufficient vitamin D status, pediatric societies such as DGKJ or ESPGHAN recommend a daily intake between about 400 IU and 800 IU and appropriate outdoor activities (Brägger et al. 2013, Reinehr et al. 2018). In Germany, vitamin D deficiency is rare in in- fancy due to the very effective vitamin D pro- phylaxis during the first 12–18 months of life with 400–500 IU, the costs which are covered by health insurances. After this time, no effort is made to guarantee a sufficient vitamin D status. This is surprising considering the high need for vitamin D in this critical time period beginning with puberty in which the assembly of healthy bones and an optimal peak bone mass is of paramount importance not only for growth and development but for health in later life. Therefore, a particular emphasis should be put onto this critical time period in the first 20 years of life (Fig. 1).
The existing recommendations, however, cannot be followed in practice. To eat a variety of foods containing vitamin D ignores the accepted fact that food is a very poor source for vitamin D and contributes only about 5–10 % to the vitamin D status. The very detailed inst- ructions of national and international societies to get enough sunshine (e. g. 20 min between 11 and 3 pm (Reinehr et al. 2018)) seem unrealistic to be followed by children and adolescents. More important, the recommendations are based upon studies by M. Holick‘s group in Boston (USA) but has not been verified for countries in the middle of Europe. In this con- text, it is widely accepted that at a geographic latitude of >40° N there is usually no skin vita- min D production in the winter times, i.e. from October to March (Zittermann 2010).
As the daily vitamin D supply from food com- prises only about 50–100 IU, some 500–700 IU need to be obtained from other sources (Kunz and Zittermann 2016).
As there is hardly any skin vitamin D production in winter, an improvement of the vitamin D status is difficult to achieve without the intake of vitamin D enriched food or supplements. However, vitamin D supplements are often not recommended by health authorities because of their potential negative effects, although there is no scientific evidence for a risk of hypervitaminosis D at these levels of intake, not even for high risk groups. It is important to emphasize that Vitamin D itself is inactive. Only if required, it will be converted into its active form 1,25(OH)2D (hormone) in the kidney (Holick 2017).
This activation is largely independent of the dietary vitamin D intake and from synthesis in the skin. No negative effects have been observed even after the intake of very high amounts. It is misleading for the general population that even in scientific publications there is often no distinction made between data obtained by the inactive native vitamin D and the hormonal form of vitamin D, i.e. the extremely potent 1,25(OH)2D; the latter is never recommended or given for preventive reasons!
The human body has several control mechanisms preventing a strong increase in 25 OH D, and hence potential negative effects: a local increase of vitamin D in the skin will finally lead to a self-regulated degradation within the skin, the transport binding proteins (DBPs) have a high capacity to bind large amounts of vitamin D and metabolites with the highest affinity for vitamin D and 25 OH D and, most importantly, there is a strong endogenous control of the renal production of the active vitamin D metabolite, 1,25(OH)2D, which will be synthesized only if the hormonal form is required.
As prevention of diseases is of paramount importance – and all authorities agree on this – it has to be underlined that the current cut-off for a sufficiency status is at least >50 nmol/L 25 OHD (IOM: Ross et al. 2011, ESPGHAN: Brägger et al. 2013, DGKJ: Reinehr et al. 2013) (Fig. 2). Other international societies recommend even much higher 25 OH D levels as only then can an increase of PTH with its potential negative effects be pre- vented. 25 OH D concentrations below 50 nmol/L are considered as “insufficiency” or even “deficiency” (Fig. 2). To be effective preventing a disease requires to start at an early point when vitamin D deficiency has not yet established. Therefore, if pediatric and nutrition societies consider a vitamin D status between 20 and 50 nmol/L as insufficient, then steps to improve this situation are strongly needed at this point in time and not waiting until a disease has developed.
In the following we summarize important issues regarding vitamin D, some of which are
often misinterpreted in the public as well as in scientific discussions:
Groups at high risk are, e. g., children and adolescents, older people, pregnant and lactating women;
The recommended intake for children and adolescents is about 600–1000 IU/d, and even higher for children in risk groups (ESPGHAN: Brägger et al. 2013);
As the vitamin D intake (only 50–100 IU/ day) via food is negligible, supplementation of the missing 500–700 IU is required;
In children and adolescents vitamin D status, measured as serum 25 OH D, is often low which puts those groups at a high risk for negative effects, e.g. on bones;
Skin vitamin D production through UVB can be extremely effective; however, it is often prevented by the strongly re- commended use of sunscreen for cancer protection; in addition, in Germany and in countries at the same latitude, it is not effective in 4–6 months (October to March);
The assumption that storage of vitamin D in summer as a depot to be used in winter is not supported by the often insufficient vitamin D status in overweight and obese individuals;
The assessment of the vitamin D status relies on serum 25 OH D measurements. The classification according to IOM, to which ESPGHAN and DGKJ adhere to is shown in (Fig. 2);
It is often argued that increasing the daily vitamin D intake would easily lead to a high risk for potential negative effects of vita- min D. However, within the recommended intake, there is no evidence for any deleterious effect in the general population. The official statements regarding safety aspects of the IOM and EFSA to which DGKJ and ESPGHAN adhere, are given in (Fig. 3)
According to the recommendations of the EFSA (European Food Safety Agency, 2012)
and the Institute of Medicine (USA) 4,000 IU/day are physiologically safe, even during pregnancy and lactation (Fig. 3). Neonates should not receive more than 1,000 IU/ day, young children up to 1 year of age not more than 2,000 IU/day. The upper limit for
older children, adolescents and adults is 4,000 IU/day (Kunz/Zittermann 2015).
Not recommending supplementation or food enrichment because of potential ad- verse reaction ignores the high risk for vitamin D deficiency in large parts of a population (Fig. 4).
Vitamin D is one of the few nutrients for which the coverage of the recommended intake can only be met most of the year by taking supplements or by food enrichment strategies.
Finally, the often made argument that at 25 OH D level classified as insufficient ”because rickets is not seen in practice” can be questioned as this would mean that initiatives to treat the disease would begin only at very low levels of 25 OH D corresponding to a deficiency status according to the classification of the pediatric societies. Preventive steps, however, need to start much earlier; indeed, at a point in time when 25 OH D concentrations are reached, which is considered as insufficient according to the classification show in (Fig.2). For example, if 30–50 % of the German population are observed to have 25 OH D levels between 20–50 nmol/L, (ref) efforts are urgently needed to improve this situa- tion and to guarantee at least the agreed minimum of about 400–1,000 IU/day for healthy bones of young children and adolescents; also, because of the long lasting effects of healthy bones later in life.