Bakos József, Mikó Péter
Fodor József Országos Közegészségügyi Központ, Országos Frédéric Joliot-Curie Sugárbiológiai és Sugáregészségügyi Kutató Intézete, Budapest.
Orv Hetil. 2007 Feb 18;148(7):319-25. doi: 10.1556/OH.2007.27840.
The vitamin D3 formation in skin is the most important natural source of vitamin D demands of humans. The key step of the phototransformation of provitamin D into previtamin D from which the vitamin D3 is formed by thermal conversion. According to studies run at the latitudes of Hungary the UV-B radiation in winter time is not satisfactory to ensure the need of the vitamin D, which can result in vitamin D 3 deficiency and increases risk of osteoporosis.
The aim of this study was to verify whether in the Hungarian population the UV radiation from the Sun ensures the daily synthesis of 1000 IU vitamin D3, or Vitamin D deficiency could occur in the winter and spring months which are less favourable in terms of UV exposure.
The data of UV-B radiation reaching the Earth's surface were used for the evaluation. These data based on regular measurements in Budapest. According to the average of UV-B radiation of each months the "best case scenario" of vitamin D3 production was estimated by using the most optimal conditions of vitamin D synthesis.
It was calculated, that the effective UV irradiance reaching the Earth's surface at noon in Budapest is the highest in July, while the lowest is in December. The difference between these two months is more than 35-fold for July. In the period between November and March more than 200 minutes have to be spent outdoor to ensure the production of satisfactory amount of vitamin D in skin. On one hand, it is irrealistically long time because it exceeds the duration of maximum irradiation around noon which was the basis of our calculation. On the other hand, if only the face and hands are uncovered then the required radiant exposure exceeds the 1 minimal erythemal dose, i.e. the skin would be burnt.
Based on our calculations it was found, that in Budapest more than 95% of yearly effective UV-B radiation is measurable in the period between March and October. Therefore it can be assumed that the UV-B radiation would not be sufficient in the period between November and February, even if its efficacy would not be limited by clothing and less time spent outdoor which are anyway characteristic and necessary in that part of the year.
皮肤中维生素D3的形成是人类维生素D需求的最重要天然来源。维生素原D光转化为前维生素D是关键步骤，前维生素D通过热转化形成维生素D3。根据在匈牙利纬度地区进行的研究，冬季的UV-B辐射不足以满足维生素D的需求，这可能导致维生素D3缺乏并增加骨质疏松症的风险。
本研究的目的是验证在匈牙利人群中，来自太阳的紫外线辐射是否能确保每日合成1000国际单位的维生素D3，或者在紫外线暴露条件较差的冬季和春季月份是否会出现维生素D缺乏。
使用到达地球表面的UV-B辐射数据进行评估。这些数据基于在布达佩斯的定期测量。根据每个月UV-B辐射的平均值，利用维生素D合成的最优化条件估算维生素D3产生的“最佳情况”。
经计算，布达佩斯中午到达地球表面的有效紫外线辐照度在7月最高，而在12月最低。这两个月之间的差异对于7月来说超过35倍。在11月至3月期间，必须在户外花费超过200分钟才能确保皮肤中产生足够量的维生素D。一方面，这是不切实际的长时间，因为它超过了我们计算所依据的中午最大照射持续时间。另一方面，如果仅露出脸部和手部，那么所需的辐射暴露超过1个最小红斑剂量，即皮肤会被晒伤。
根据我们的计算发现，在布达佩斯，每年超过95%的有效UV-B辐射在3月至10月期间是可测量的。因此可以假设，即使紫外线辐射的功效不会受到衣物和户外活动时间减少的限制（而这在一年中的那个时段无论如何都是常见且必要的），11月至2月期间的UV-B辐射也将不足。
