UVB radiation changes 7 dehydrocholesterol

Midday sun holds the key to good health (26 May, 2005)

Scientists at The University of Manchester have today unveiled new research which claims that going out in the midday sun, without sunscreen, is good for you.

The research, led by ultra-violet radiation expert Ann Webb, supports claims that exposing unprotected skin to the sun for short periods helps the body to produce essential Vitamin D.

Dr Webb has produced new figures which not only predict when is the best time to expose unprotected skin to the sun in order to maximise Vitamin D production, but also for how long - depending on location. She has calculated that 'ten to fifteen minutes* at noon' is the optimum time for the average person in the UK to spend in the sun without the use of sunscreen.

"Our calculations have found that the best time to be out in the sun if you want to maximise Vitamin D production and its benefits is midday. This is when the sun is highest in the sky and this is when there is more UVB radiation in the spectrum which triggers Vitamin D production in the skin," says Dr Webb.

Vitamin D promotes the absorption of calcium and phosphate from food and is essential in the formation of bones and teeth. A deficiency of Vitamin D leads to a failure of the bones to grow and causes rickets in children and osteoporosis in adults. Recent research also suggests that Vitamin D can help reduce the risks of colon, breast and prostate cancer.

Dr Webb, says: "The two sources of Vitamin D are through your skin or through foods like sardines (fatty fish), but because our everyday diet isn't very rich in the vitamin it is essential that we get it from the sun."

"You do not need to sunbathe to get your Vitamin D and we are not advocating people do not protect themselves with sunscreen, but if you put sunscreen on before you step out of the house you will not reap any health benefits provided naturally by the sun. After a short period of unprotected exposure you should cover up or put on sunscreen to avoid sunburn."

The research, which has been carried out in conjunction with experts at the Norwegian Institute for Air Research, uses computer simulations based on global UV data to calculate optimum times for Vitamin D production based on season, time and latitude. The programme can be run for any time of day and can calculate optimum exposure times for any location in the UK or abroad.

*Figures for optimum Vitamin D sun exposure this Bank Holiday weekend:

Edinburgh - 11 minutes
Manchester , Leeds, Liverpool - 10 minutes
London - 9 minutes
Devon and Cornwall - 9 minutes
Marseille - 7 minutes
Madrid - 7 minutes
Athens - 6.5 minutes

Figures based on full sun exposure at midday on Bank Holiday Monday (May 30th) with a cloudless sky for a fair-skinned person wearing t-shirt and shorts or skirt. People who tan easily would need to spend slightly longer in the sun, and naturally pigmented people require even more sun exposure.
For further information:

Simon Hunter, Media Relations Officer, telephone: 0161 2758387/07717881569

Notes to Editors:

Dr Ann Webb is a Reader in the School of Earth Atmospheric and Environmental Sciences part of The University of Manchester's Faculty of Engineering and Physical Sciences.

This research is based on the findings in the Paper 'Calculated Ultra Violet Exposure Levels for a Healthy Vitamin D Status' co-authored by Dr Ann Webb and Dr Ola Engelsen at The Norwegian Institute of Air Research.
Calculations have been made on the basis of the UV equivalent of an oral intake of a 1,000 international units of vitamin D per day as recommended by Michael Holick.

Explanation of how UVB creates Vitamin D:

UVB radiation changes 7 dehydrocholesterol, present in skin cells, into pre-vitamin D. This is a rapid reaction. Over the course of several hours the body's heat then changes the pre-vitamin D into vitamin D, which is picked up by a binding protein in the blood. The vitamin D is changed into its active form in the liver and kidney.

Pre-vitamin D can also be changed into other biologically inert products in the skin. This limits the amount of vitamin D that can be made in the skin at any one time. A long exposure therefore gives no benefits, only the risk of sunburn. Short, regular (daily) exposures are the best way to build up a healthy vitamin D status.

Last updated: Thu, 26 May 2005 12:35:34 BST Combining the strengths of UMIST and
The Victoria University of Manchester

SOURCE: The University of Manchester