Protecting Workers from Ultraviolet Radiation - icnirp

3.4 Systemic Effects
3.4.1 Production of vitamin D3
Protecting Workers from Ultraviolet Radiation
The best-established beneficial effect of solar ultraviolet radiation on the skin is the synthesis of
vitamin D3 (Webb and Holick 1988, Webb et al 1989). Solar radiation in the UVB waveband
photochemically converts 7-dehydrocholesterol in the epidermis to previtamin D3, which is then
converted to vitamin D3. Sunlight regulates and limits further production of vitamin D3 in the
skin to preclude a toxic level. During midday hours in the tropics or during the spring and
summer in more temperate climates, only brief sub-erythemal exposures to sunlight are required
to synthesize vitamin D3. In this case, less than 15 minutes of solar UVR exposure on the hands,
arms and face fulfils this requirement. However, in some latitudes outside the tropics, there may
be insufficient ambient UVB during the winter for this process, and this deficiency has a greater
impact for persons having highly pigmented skin and elderly persons (Webb et al 1988).
Vitamin D is known to be essential for the body’s proper uptake of calcium, which is important
for bone and musculoskeletal health. There is also evidence of an increased risk of autoimmune
diseases, including multiple sclerosis, type-1 diabetes and rheumatoid arthritis with low vitamin
D intake or low UV exposure, respectively. Some recent epidemiological studies suggest a link
between a number of cancers and low vitamin D levels. There is limited evidence for a possible
association with prostate, breast and other cancers, but somewhat stronger evidence for colon
cancer. At present, however, the evidence is insufficient to establish a causal relationship and the
questions on what is the optimal level of vitamin D and what is the amount of UV needed to
maintain an adequate vitamin D level still remain difficult to answer (reviewed in ICNIRP 2006).
3.4.2 UVR immune effects
Through photochemical reactions, UV radiation can alter various organic molecules in the skin
and these molecules may become dysfunctional and ‘foreign’ to the skin. An important task of
the body’s immune system is to seek out and destroy any “foreign intruders,” and it is therefore
conceivable that UV radiation could trigger unwanted immune reactions against the skin (this
might actually cause ‘sun allergy’) (Cooper et al 1992). It has, however, been established that
UVB exposure reduces specific immune reactions in the skin of healthy people and this is likely
to constitute a healthy response to avoid any undesired immune reaction against the UVR
exposed skin. This effect is usually only temporary, but it can have clear drawbacks when it
coincides with an infection or with abnormal cell growth. For these conditions, UVR exposure
of the affected area should be minimized.
Not only infections in the skin can be aggravated, but also internal infections. The common ‘cold
sore’ that is evoked by sun exposure appears to be a good example of an infection (by
stimulating the Herpes simplex virus) in humans brought forth by UVB exposure. In all, there is
much evidence that UV radiation affects immunity and, because of that, can aggravate infections
and allow the development of (skin) cancers. Some systemic diseases such as Lupus
erythematoses can also be aggravated by UVR exposure.
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