Touch of sun good for you

English tourist Katie Walton gets her dose of vitamin D as she sunbathes at Okahu Bay on a warm Auckland day. Picture / Kenny Rodger

The sun, for so long the enemy of our skin, has become our friend again - at least for a few minutes a day.

After decades of warning that too much sun can cause melanoma, health authorities have now formally acknowledged that too little sun is also a health risk, because of vitamin D deficiency.

Exposure to the sun's ultraviolet rays produces vitamin D.

Around half of adults and a third of children in New Zealand have insufficient vitamin D, according to Health Ministry surveys. Three per cent of adults are seriously deficient.

A shortage of vitamin D results mainly in bone weakness, but studies are now finding associations with numerous conditions, including heart disease, bowel cancer and obesity.

Some people are at increased risk of vitamin D deficiency, including the housebound, those with darker skin and veiled and robed Muslim women.

The state-funded SunSmart Partnership issued a position statement on vitamin D this week, after forming an experts group to grapple with the dilemma of sun exposure.

Its findings reflect changes in Australia's skin cancer messages, which were interpreted in March by public health specialists as a revolution in the country's attitude to the sun.

SunSmart spokeswoman Wendy Billingsley said the group found sun protection was still warranted in times of high UV radiation. This was unlikely to put people at risk of vitamin D deficiency. In summer, most should get enough sun for adequate vitamin D from normal activities.

People who burned easily might need only five minutes' sun exposure - outside the high-risk hours of 11am to 4pm. Those who tanned easily or had darker skin would need possibly up to 20 minutes. But during winter, especially in the south of the country, people might not get enough UV rays for an adequate vitamin D level. Bodily stores of the vitamin drop in winter.

Darker skin needs more sunlight to make vitamin D, putting people with these skin types at greater risk of vitamin D deficiency, especially in the south. But they also have less risk of skin cancer. The position statement says people at risk of vitamin D deficiency should see a doctor about taking a supplement.

Dr Richard McKenzie, a National Institute of Water and Atmospheric Research scientist, said that during summer, Auckland's average UV index rating was 13, about 30 per cent higher than Invercargill's. But in winter, Auckland averaged 2, 100 per cent more than the southern city.

The same latitudes in NZ and the Northern Hemisphere received similar amounts of UV in winter but NZ had much more in summer.

This was due to factors including lower levels of air pollution and ozone over New Zealand, and the Earth passing closest to the Sun in the southern summer.

Summer safety advice

* Continue to avoid the sun from 11am to 4pm during the warmer months, or cover up, wear sunglasses and use sun screen.
* Outside that time, to get vitamin D, expose your face, forearms and hands to the sun for a short time each day.
* Length of exposure needed depends on skin darkness.
* Five minutes for fair-skinned person who burns easily.
* Up to 20 minutes for darker skin types.
* During winter, people might not be able to get enough vitamin D from sun exposure.