Information on Vitamin D Synthesis / Erythemal UV

Enter the PC site from the above banner Japanese site



  • This mobile site for handy search was launched with the aim of making it easy to know how much sun exposure time is appropriate for 10 μg vitamin D synthesis in the body under the sun.
  • More detailed information is available at the PC site, which can be reached from the banner of "Information on Vitamin D Synthesis / Erythemal UV " at the top of the page.
  • It is also important to take vitamin D from foods (e.g., mushrooms such as Jew's ear and fish such as sardines and salmon). Especially in regions at high latitudes, enough vitamin D synthesis is difficult due to low UV energy in winter. In such a case, please try to ingest a sufficient amount of vitamin D from foods, or in some cases, consider using nutritional supplements.

Description of data

  • In the "Real Time Data", recommending sun exposure time and sun exposure time to reach MED (minimum erythemal dose) based on the current UV observation data are displayed according to the selection of the monitoring station and the exposing skin part. "Average of Past Data" displays former averaged values based on archived data. For details of the selection, see the explanation of "How to select data".
  • If observational data can not be obtained by some reasons, the value may not be displayed.
  • Assuming that the required intake of vitamin D is 15 μg per day in adults, 5 μg of which is ingested from food, and the remaining 10 μg is synthesized from the UV in the body, the necessary time for synthesis is calculated and displayed as the recommending sun exposure time. Please note that sunbathing of this time is not necessary everyday. It is said that vitamin D in the body is kept for about 10 days, so it is okay if you are taking sunshine on average for this period.
  • We assume an average Japanese skin type as skin photo type Ⅲ. Appropriate exposure time increases and decreases depending on the type of skin. For details please see the PC site.
  • The UV radiation in the wavelength range from 280 nm to 315 nm contributing to the vitamin D synthesis are also known to have adverse health effects such as increased risk of skin cancer and cataract development by prolonged exposure at the same time. To minimize the adverse effect on this site, we calculate the amount of UV exposure at which sunburn will begin as the minimum erythemal dose (MED) and call attention not to exceed the exposure time to reach it. If more exposure is expected, use of sunscreen etc. is recommended.

How to select data

  • In "Selection of Exposing Skin Part", you can select one of two cases. A face and hands are exposed (assuming the exposed area of 600 cm2) in the season other than summer, and arms and legs are also exposed (1200 cm2 is supposed) in summer time.
  • In "Selection of Monitoring Station", please select a station close to the area where you live from 12 locations nationwide. If you do not have a monitoring station close to you, it is a good idea to select the nearest stations and use the averaged value prorated according to the distance as a guide.
  • In "Selection of Data Type", it is possible to select the real time data or average of past data. In "Real Time Data", the recommended sun exposure time calculated based on the observed amount of UV radiation is displayed. However, please be aware that there is a delay of about one hour from observation to display.
  • If you select "Average of Past Data" in "Selection of Data Type", the recommending exposure time around noon corresponding to the average weather at this time of year (beginning, middle and end of each month) is displayed. Furthermore, by selecting season from the drop list, the recommending exposure time for any season (from beginning, middle and end of each month) is displayed. This average value is based on actual observation data at monitoring station after 2014.