Information on Vitamin D Synthesis / Erythemal UV


Exposure Time for Vitamin D Synthesis / MED (Tsukuba)

The time required for 10 µg Vitamin D to be produced is calculated for a skin area of 600 cm2 exposed to solar radiation, which correspond to the face and the back of both hands. Here skin photo type (SPT) Ⅲ is adopted. The skin type of Japanese people is generally SPT:Ⅱ - Ⅳ and most Japanese have SPT: Ⅲ. The time can be reduced if the exposed area is larger, e.g. 1200 cm2, by exposure of additional parts of arms and legs. The values are shown simultaneously in the figure.

The mean time to reach MED (Minimal Erythma Dose) which causes skin erythema is also shown in the figure for every 30-minute mean. It is well known that excessive exposure to UV causes skin cancer, eye cataract etc. However, harmful influence causes dermatosis such as sunburn, skin cancer etc. only in the exposed skin .

The gray area shows that an exposure time over 60 min is required for the production of 10 µg Vitamin D, and to reach MED.

The UV environment on the ground differs according to the location, the season and the time of the day as well as meteorological conditions such as cloud cover. Moreover, it should be noted that the appropriate exposure time changes with the individual’s skin type. Therefore, you should know your own skin type. For people who have other skin types than SPT: Ⅲ, it is possible to calculate the time for MED and the production of 10 µg vitamin D estimated from the result of SPT: Ⅲ.

Skin Types
SPT MED (J/m2) Correction factor Reaction to sun
250 0.83 Usually burns easily, tans with difficulty
300 1.00 Burns moderately, tans gradually
450 1.50 Pigmented

In addition, the amount of vitamin D necessary for health can be taken from food such as fish. People who live in the northern part of the Japanese archipelago where UV radiation is least, especially in the winter season, need to take vitamin D supplements.

Appropriate exposure time at every site shown below can be seen below.
Cape Ochi-ishi (Hokkaido), Rikubetsu (Hokkaido), Tsukuba (Ibaraki), Cape Hedo (Okinawa), Hateruma (Okinawa).

Monitoring Stations