Influence of narrowband UVB phototherapy on vitamin D and folate status.

BACKGROUND: A variety of studies have shown beneficial effects of different types of phototherapy in skin disorders. Such therapy leads to enhanced cutaneous vitamin D synthesis, which may be one of the mechanisms of action. Furthermore, another nutrient, folate, can probably also be influenced by UV radiation. OBJECTIVE: The aim of our study was to investigate the influence of low-dose narrowband UVB (nUVB) phototherapy of patients with psoriasis, atopic eczema and other skin disorders on serum levels of 25(OH) vitamin D (the serum marker for vitamin D status) and on serum and erythrocyte-folate. METHODS: 25(OH) vitamin D (25(OH)D), serum and erythrocyte-folate levels were measured before and after low-dose nUVB (TL-01 tubes) phototherapy of these patients. The spectrum of the TL-01 tube was compared with the solar spectrum, and the efficiency spectra of vitamin D photosynthesis were calculated. RESULTS: For patients with a high initial 25(OH)D serum level (> 80 nmol/l), no significant (P = 0.36) increase in 25(OH)D levels was seen, in contrast to patients with a low initial level (< 80 nmol/l) where a significant increase (P < 0.001) was observed. The increase was 30-60%, depending on the UVB dose (2.35-13.4 J/cm(2)). No significant nUVB-effect was found on the erythrocyte and serum-folate level. CONCLUSION: Low-dose nUVB treatment gives a significant increase (P < 0.001) of the vitamin D status in persons with low initial levels of 25(OH)D, but no effect on the folate level.

Photodegradation of 5-methyltetrahydrofolate in the presence of Uroporphyrin.

The main form of folate in human plasma is 5-methyltetrahydrofolate (5MTHF). The observation that folate in human serum is photosensitive supports the hypothesis that humans developed dark skin in high ultraviolet fluences areas in order to protect folate in the blood from UV radiation. However, folates alone are quite photostable. Therefore, in this study, we examined for the first time the photodegradation of 5MTHF in the presence of the endogenous photosensitizer uroporphyrin (Uro), which is sometimes present in low concentration in human serum, under UV and near-UV light exposure. We found strong indications that while 5MTHF alone is rather photostable, it is degraded quickly in the presence of Uro. Using deuterium oxide (D(2)O) as an enhancer of the lifetime of singlet oxygen and the singlet oxygen sensor green reagent (SOSG) as a scavenger of singlet oxygen, we have found that the photodegradation most likely proceeds via a type II photosensitization. Our results show that singlet oxygen is likely to be the main intermediate in the photodegradation of 5MTHF mediated by Uro. Our findings may be useful for further studies the evolution of human skin colours.

5-Methyltetrahydrofolate is photosensitive in the presence of riboflavin.

5-Methyltetrahydrofolate (5MTHF) is the main form of folate in human plasma, and an important vitamin for human health. Photodegradation of folates may have played a role in the development of different human skin colours. 5MTHF can be degraded directly by exposure to ultraviolet radiation or by exposure to visible light in the presence of endogenous sensitizers like riboflavin (RF). These photochemical reactions were studied by absorption spectroscopy. While 5MTHF is stable under UV and visible light exposure in pure aqueous media, it is quickly degraded in the presence of RF during UVA and blue light exposure. The degradation of 5MTHF is dependent on the concentration of RF, but not on the concentration of 5MTHF itself. UVA and blue light gave similar reactions. Further investigations are necessary to evaluate the consequences of large light exposures in vivo in humans. Our findings should be taken into the ongoing discussion about the development of human skin colours. Due to the presence of RF in human blood, folate can be significantly degraded during prolonged or intense blue light exposure. Thus, a dark skin colour may be favourable for prevention of folate degradation under high solar fluence rates, such as in equatorial areas.