Frequently Asked Questions

  • How much UV do I need in order to make enough vitamin D?

    This is a complicated question, and at present we do not have all the knowledge we need to give a complete answer.

    However, the amount of UV you need (and could practically achieve) will not be enough to give you sunburn - you should always cover up/protect your skin before you get a sunburn.

    The skin also has a clever protective mechanism that stops you making too much vitamin D at one time (vitamin D can also be toxic), so after a short exposure more UV becomes ineffective for vitamin D production.

    The information we need to answer the question is:

    • How much vitamin D do we need - this is currently a matter of debate. We know how much is required to avoid rickets (400 IU is recommended), but how much is required for complete bone health, or to gain some of the other potential benefits of vitamin D, is less well defined. One common indication is 1000 IU, while an extreme suggestion is 4000 IU.
    • Skin type. In the same way that pigmentation protects against sunburn by absorbing UV, so it reduces the probability of making vitamin D by absorbing much of the necessary UV before it reaches the relevant parts of the skin.

    • Area of skin exposed. Vitamin D moves from the skin into the blood, where it is changed into its active form. Any exposed skin contributes to the circulating levels of vitamin D, so the more skin exposed, the more vitamin D will be made in a given exposure time.

    Finally, how quickly you could achieve that UV exposure will depend on where you are and when i.e. on the UV index at the time of exposure.

    You can make calculations for many different conditions, times, places and skin types by using this online calculator.

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