Kiwis are extremely proud of the way we punch above our weight on the world stage. But when it comes to skin cancer, our world-leading position is cause for concern, not celebration. As country, our incidence of melanoma – the deadliest form of skin cancer – is around four times higher than Canada, the US and the UK. In New Zealand, new skin cancers total around 67,000 each year, compared to total of 16,000 for all other forms of cancers.
In fact, if you’re New Zealander there’s one in 17 chance you’ll develop melanoma in your lifetime, while research suggests two-thirds of us will develop non-melanoma skin cancer. But New Zealand’s high incidence of skin cancer isn’t wholly down to sun-seeking attitude. According to the National Institute of Water & Atmospheric Research (NIWA), differences in ozone and pollution levels, and sun-earth separation mean the peak ultraviolet (UV) intensity in New Zealand during summer is approximately 40 percent higher than corresponding latitudes in the Northern Hemisphere.
But while skin cancer is by far the most common cancer affecting New Zealanders, it is also one of the most preventable. Over 90 percent of skin cancers are due to excess radiation exposure.
However, steady stream of recent media articles has raised the question of whether our strong ‘sun smart’ message means some New Zealanders are now not receiving enough sunlight to synthesise the vitamin D in our skin. 2005 University of Otago study of nearly 3000 New Zealanders found that 48 percent had insufficient levels of vitamin D for optimal health.
Vitamin D is needed for the healthy development of bones, muscles and teeth and may also offer some protective effects against osteoporosis, multiple sclerosis, Type 1 diabetes and certain types of cancer, such as colon cancer. In general, those with dark skin require greater amount of sunlight for its production than those with fair skin.
The conundrum is that the optimal levels of UV for the synthesis of vitamin D are also those that cause sunburn – three or higher on the UV index (the UV index is an international measure of UV intensity that ranges from one to 11+). So how do we marry our need for vitamin D with the need to be sun smart? As with much health advice, it comes down to matter of balance and individual need.
Research by NIWA scientist Richard McKenzie suggests that, for those with fair skins, as little as five minutes in sunlight might be needed for the synthesis of vitamin D. During summer, his research suggests the sun should be avoided between 11am and 4pm, with any exposure to sunlight taken outside these hours when the UV index is between one and three.
The Cancer Society says balance between adequate vitamin D levels and increased risk of skin cancer is needed, and that “sensible sun protection is unlikely to put people at risk of vitamin D deficiency”. Between September and April, it says most people should be able to achieve adequate vitamin D levels through usual UV exposure outside peak times, and recommends those at higher risk of vitamin D deficiency, such as the elderly, housebound or people with dark skins, talk to their doctor about their individual vitamin D requirements.
The Cancer Society’s message on sun exposure remains as strong as ever – anyone who is exposed to UV light is at risk of skin cancer. The society recommends that sun protection is used between the months of September to April, or when the UV index is at three or higher.
Peter Tynan is chief executive of Southern Cross Health Society.
