Spotlight on.. Vitamin D
Sunlight is the best source of vitamin D, but safe sun exposure is still essential.
Out of all the vitamins, D is the most contentious. It’s necessary for calcium absorption, and to keep bones and muscles strong, but the best way to get it is to go into the sun without – gasp! – full SPF protection. Given we have high rates of skin cancer, but one in three New Zealanders are vitamin D deficient, that makes it rather a delicate conundrum. “You need UV-B to make vitamin D,” explains Professor Rebecca Mason. “But ultraviolet also causes skin damage, particularly to DNA. If that isn’t properly repaired it can lead to skin cancers.”
Sunscreen blocks UV-B, which means it also interferes with vitamin D production. That’s why total sun avoidance is no longer recommended. “Around 2005 it was recognised by medical and scientific organisations that there were benefits as well as risks from sun exposure,” says Professor Mason. “We know low vitamin D puts people at higher risk of falls and fractures and is associated with worse outcomes in pregnancy. There’s also evidence that vitamin D may help people fight infections, and that it protects to a small extent against inflammation and some auto-immune diseases.”
A balanced approach for most Kiwis (anyone not at higher risk of skin cancer) is to plan for vitamin D exposure in short bursts and the best time to do that is now. “You need to build up your skin defences when the sun is not so strong and keep sun exposure short,” says Professor Mason, who cautions that excess sun exposure is never a good idea, and not just because of the skin cancer risk. “If you keep exposing skin to sunlight for too long, you start to break down the vitamin D that has been made before it can be absorbed into the body.” How much UV-B is enough? That depends on where you live, how much skin is exposed and how much pigment is naturally in your skin (the darker your skin, the longer it takes to make vitamin D). “As a rough rule of thumb, no matter where you are during summer and the later parts of spring and early autumn, if you have light to slightly dark skin and go out at least four times per week between mid-morning and mid-afternoon wearing the equivalent of shorts and a short-sleeved shirt, then 5-10 minutes in the sun should be enough to maintain vitamin D at acceptable levels,” says Professor Mason. “In the early morning or late afternoon not much, if any, vitamin D will be produced. The main message to remember is that for sunlight, like many other things, moderation is key.”