Vitamin D supply in winter
Prevention instead of cure

The dismal weather during the long grey winter months has a depressing affect on most people and makes them moody and bad-tempered. The low intensity of the sunlight at this time of the year is simply too weak to have any cheering effect on the psyche. But it is not just our pysche which suffers from lack of sunlight, the functions of our organs are negatively affected by insufficient exposure to sunlight, in other words, our whole feeling of well-being is notedly impaired.
Together with the beneficial, bio-positive effect of UV irradiation on the human organism, the introduction of vitamin D synthesis into the skin is of special significance.

Vitamin D₃ - the „sun hormone"

We have known for a long time that the sun is the most important source for the formation of vitamin D in man and animals. Under the influence of UV irradiation from the sun, 7-dehydrocholesterol, which occurs in the skin, reacts to become provitamin D, so-called cholecalciferol. The real vitamin D₃-effective substances however, do not form until after further chemical conversions have taken place (hydroxylation) in the kidneys and the liver from where organs which are vitamin D-dependent are supplied, such as the intestinal mucosa and the bones.The effective UV rays for forming vitamin D₃ are in the 255 to 320 nm range and have a maximum effectivity at 295 nm. The graph of the spectrum of activity illustrates why we have an insufficient supply of vitamin D₃ during the winter months at our latitudes.

In our climatic zone in the period approximately October/November until February/March practically none, or only an extremely limited number of natural UV rays with a wave length of below 320 nm reach the earth´s surface. However, as the spectrum of activity clearly shows, the vitamin D₃ synthesis is triggered solely by UV rays of this quality. That means that during the period mentioned, natural sunlight as a source of vitamin D₃ for our organism is not available.
It therefore comes as no surprise that the vitamin D level in blood serum is then considerably lower than at the end of the sunny summer months, even in the average person.

many people in winter is close to, or already below, the minimum values acceptable from a medical point of view. This result not only demonstrates the vital role of natural sunlight in the supply of vitamin D but also refutes the widely-held supposition that the body is sufficiently provided for with vitamin D in the form of the food we eat. Were this so, then the serum levels would not be so low in the winter months.

Vitamin D is more than just a vitamin

On the contrary, it must be assumed that approximately one third of the healthy population are under-supplied with vitamin D in the months from January to March. A deficiency of this nature, or even an already existing deficiency, would appear to give even more reason for concern if we take into consideration that in elderly people especially, a low vitamin D level goes hand-in-hand with low bone density, so that a sub-clinical vitamin D deficiency, that means one that does not yet display any symptoms of disease, must be regarded as a risk factor for osteoporosis (reduction in quantity and quality of the bones). These findings are all the more remarkable if we consider that about 20% of all women are affected by osteoporosis after the menopause. Furthermore, the various functions of vitamin D in all the organs are to be taken into consideration in connection with possible deficiencies. Nowadays, we know that vitamin D is more than a vital substance. The effectivity profile goes beyond that of a vitamin. As vitamin D controls and regulates metabolism in so many ways, it is placed today in the category of hormones. In addition to its well-known effects on bone metabolism (calcium and phosphate metabolism), vitamin D influences the immune system, the musculature, the glandular and the nervous system and the epidermis. In many cases, it is assumed that all the known effects of UV rays concerning health care and prophylaxis can be attributed to vitamin D₃ synthesis. It appears therefore to be all the more important to ensure sufficient provision of vitamin D throughout the year. This is the only way to prevent any possible deficiencies which can definitely lead to more serious illnesses. A solarium, where the emission spectrum reaches UV values below 320 nm presents itself as a prophylaxis thus covering at least a part of the action spectrum for vitamin D₃ synthesis.

Vitamin D₃ and bone metabolism

During this study, a group of healthy people were exposed to commercial sunlamps 10 times in 12 days whereby the dosage always remained under the level which would cause the skin to redden.

   Vitamin D and parathormone levels after sunlamp treatment with
            (a) Lifesun       (b) Eurosun

This sunlight treatment led, on the one hand, to a considerable increase in vitamin D-effective substances and, on the other hand, to a reduction of the parathormone level in blood serum, which was, in some cases, still evidented four weeks after the series of exposure (A. Falkenbach, 1995).

The particular importance of parathormone for bone mass

Parathormone has an undesirable effect on bone metabolism as it is responsible for bone resorption, i.e. it furthers bone destruction. If the concentration of parathormone in serum is reduced, this will automatically lead to a reduction in bone destruction. In young people, therefore, a low parathormone level results in a higher maximum bone mass, which is, in turn, advantageous in later years. This greater reserve of bone mass means that the inevitable physiological deterioration of the bones in old age is not so strongly pronounced. This also means that in the later years of life, there is protection against osteopenia and osteoporosis and a reduced risk of fracturing. But even older people, already suffering from the effects of bone deterioration can benefit from UV- exposure from a suitable radiation source to reduce these effects. In such cases, higher concentrations of vitamin D and lower concentrations of parathormone in the serum are advantageous to ensure that the consequences of increasing bone demineralization to not affect the quality of life too much. This applies especially to persons with limited mobility. During the winter months,those persons in residential care who are still mobile have a vitamin D level which is just about on the pathological borderline whereas those confined to their beds have even more critical values, which underlines clearly the presence of a deficiency in UV exposure (P. Knuschke et al., 1992).

Vitamin D values within the normal range -
even small UV doses are sufficient

This group of people can also benefit from a suitable UV exposure to promote the vitamin D₃ synthesis and even when only parts of the body are exposed (face and hands, or the upper part of the body), levels are reached which lie within or at the limits at normal.

the provision of vitamin D into the normal range, it is sufficient to use lower UV exposures than are usual for tanning purposes.

Vitamin D tablets or sunlight treatment ?

Those who criticize vitamin D formation by means of UV irradiation refer repeatedly to oral treatment with which deficiencies can likewise be prevented; as the studies mentioned here have shown. However, the vitamin D tablets must be carefully dosed to avoid toxic reactions (symptoms of poisoning) and hypercalcaemia (over-calcification). Fortunately, there is no such risk with UV-initiated vitamin D₃ synthesis. An over-production of vitamin D following UV-exposure is not possible as, in such cases, inactive substances (lumisterol and tachysterol) are formed instead of the previtamin. This natural regulating mechnism provides protection against surplus formation of vitamin D with longer UV exposure times. Furthermore, the vitamin-ineffective substances have a storage function. When necessary, i.e. when the vitamin D level drops, they are re-converted into the active previtamin D.

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