As we head towards summer, a Deakin researcher says that most Australians don't need vitamin D added to food, should ditch the vitamin D supplements which can lead to overdose, and that a couple of minutes in the sun daily is enough to keep vitamin D levels normal.
Emeritus Professor Caryl Nowson, from Deakin's Institute for Physical Activity and Nutrition, says that in late spring and summer it's important to wear sunscreen during the day, but that it's just as vital to get enough vitamin D from its natural source – ultra violet rays from the sun.
"For many people the fix for not getting enough sunshine is a vitamin D supplement. While supplements have a place, it's for the minority of the population," Professor Nowson said.
"Supplements are only useful for those where the risk of vitamin D deficiency is high and low vitamin D status has been identified with a blood test. It is preferable for the body to make natural vitamin D because, unlike with supplements, there is no possibility of an overdose.
"However, this is not possible for everyone. Frail elderly people or those who are in hospital or rehabilitation are at genuine risk of not getting enough ultra violet rays from the sun. Also people with naturally very dark skin, nightshift workers with limited sun exposure and breastfed babies of vitamin D deficient mothers are at the greatest risk of deficiency."
Professor Nowson says those in the high-risk group taking supplements must ensure they stick to the prescribed daily amount.
"Vitamin D supplements are available in supermarkets and over the counter at chemists. There appears to be a view among the general population that vitamin D tablets are safe and you can't have too much, as the body will expel what it uses, but that's misguided," she said.
"Overdoses are caused by megadoses of supplements, not diet or sun exposure, and are toxic."
How much time the average person – free of deficiency – needs to spend in the sun to naturally make the hormone depends on skin colour and their distance from the equator. People with darker skin need longer exposure to UV light to produce vitamin D.
"These requirements change with the seasons. In summer most people make enough vitamin D because UV levels are high and we spend more time outdoors. During these months, Victorians need just a few minutes of sun exposure mid-morning or mid-afternoon to get enough vitamin D," Professor Nowson said.
She added that longer stints of sunshine after a long winter and cold start to spring won't expedite vitamin D production and storage.
"People make the mistake of thinking they can spend more time in the sun to bring vitamin D levels back up quickly, but that's not the case," Professor Nowson said.
"The minute your skin starts to go a little pink, or red, your body stops making vitamin D. It's the body's natural way of preventing a vitamin D overdose. Vitamin D needs to be produced by the body, from sunshine, daily. It is a nutrient that is needed for health, particularly to maintain strong bones and teeth by helping the body to absorb calcium."