June 23, 2012
Vitamin D deficiencies are harmful but, as Nicole Hasham explains, debate rages over its intake.
Susan Torres wasn't just aware of the risk - it was her life's work. But even as the nutrition lecturer sat through countless conferences warning of the dangers of vitamin D deficiency, it never dawned that she was the perfect case study.
She has the risk factors: sun-shy and office-bound. But it wasn't until her naturopath suggested a blood test that the 41-year-old discovered her body was lacking in the vital hormone.
"I work in the field, I know what the problems are with low vitamin D levels. This topic comes up all the time but it just kind of washed over me," says Dr Torres, of Hampton, in Melbourne's south. "I was surprised initially but then I thought about it, and I'm a prime candidate."
A study published this week shows that Torres joins a swelling cohort: it confirms that almost one in three Australians are lacking in vitamin D.
Deficiency in the "sunshine hormone" can threaten bone health, triggering osteoporosis in older people and rickets in children. It has also been linked to mental health problems and diseases such as cancer, diabetes and multiple sclerosis.
But how best to confront the problem is subject to spirited debate, as health experts question the value of taking supplements or adding more vitamin D to our food.
Others, such as the Cancer Council Australia chief executive, Professor Ian Olver, warn against muddying the sun-safe message.
"When Slip, Slop, Slap started almost 40 years ago, the whole message was oriented towards protecting yourself from the sun," Olver says. "But when the vitamin D story came along, the message had to be modified and it's always difficult to convey complex messages like that."
Vitamin D helps retain calcium from food in the body, forming when UV radiation from sunlight hits the skin. In Australia, margarine and some types of milk and yoghurt are already fortified with the vitamin, and it occurs naturally in foods such as eggs and oily fish.
Diet alone is unlikely to keep a person's vitamin D at an adequate level, so limited exposure to the sun is recommended.
But getting the right dose can be a difficult task, says a Deakin University nutrition expert, Professor Caryl Nowson. "Our lifestyles are such that we don't spend much time outside. We work indoors, we travel in cars, and we are also aware of the cancer risk [of sun exposure]," she says.
Indoor workers are especially prone to vitamin D deficiency. A survey of Sydney office workers presented last year found 42 per cent were lacking in the hormone at the end of winter. And while levels often rise when the weather warms up, one in three workers still had low levels over summer.
Sharper awareness of the health risks has prompted an avalanche of vitamin D testing. In 2010-11, almost 3 million vitamin D tests were carried out in Australia, at a public cost of $109 million - up from 37,000 tests a decade ago.
A study co-written by Nowson, published in the Medical Journal of Australia this week, shows 31 per cent of Australians have low levels of vitamin D and more than 50 per cent of women are deficient in winter and spring.
Nowson says the results indicate that sun exposure guidelines are not being followed, and is calling on Australia to follow countries such as Canada, which has fortified foods such as orange juice and breakfast cereal with vitamin D. It follows criticism this year by the US biochemist Lyle MacWilliam, who described Australia's vitamin D recommendations as "seriously out of date". He pointed to US and Canadian authorities who, spurred on by emerging research, recently raised the recommended daily dose to 600 international units - three times the advisable intake in Australia.
Nowson believes Australia should adopt the US advice, citing studies that vitamin D deficiency contributes to falls and fractures in older people. She rejects claims that adding vitamin D to the food supply could lead to toxicity. "To take you to the upper limit, you would have to drink 10 litres of fortified milk a day, every day, and [fortification] has been done in Canada for 35 years with no toxic effects," she says.
But Associate Professor Karen Charlton, a nutritionist at the University of Wollongong, doubts that Australians are ready for vitamin D to be added to their food. "There is quite a lot of public resistance against fortification of basic food stuffs. People tend to be quite sceptical about it and don't want their food to be tampered with," she says, adding it would need intensive dietary modelling and monitoring.
She is calling for a targeted strategy that encourages risk groups to take supplements, and a revision of the sun-smart guidelines, particularly for older people. "It is a public health issue and … it is time for action, but the most appropriate action still remains to be demonstrated," Charlton says.
Torres is combating her deficiency through vitamin D and calcium tablets, but does not plan to increase her sun exposure. "I burn too easily. I'll still do all my sun-smart practices, but the way I'm going to manage this is through a daily supplement," she said.
But even that route is controversial. A large study from Denmark, to be published in August, concludes that older people who take calcium and vitamin D supplements live longer. But the benefit is apparently at odds with a report by the US Preventive Services Task Force this month, which found that low doses of the two supplements do not prevent post-menopausal women sustaining fractures.
Other unknowns, some of which run to the core of vitamin D advice, are "the big elephant in the room", says Professor Michael Kimlin, an expert in sun and health at the Queensland University of Technology. "We need to understand sun exposure times more. If people follow the guidelines, will they actually maintain a healthy vitamin D level? And how do we balance that out with the risk of skin cancer?" Kimlin says.
He says links between vitamin D deficiency and diseases such as cancer and diabetes are not fully understood. "There is a lot of science that is missing that is really important in this public debate. Until we get more evidence, we need to err on the side of caution."
In the meantime, Olver says, the Cancer Council will stick by its recommended sun exposure times. He says experts across the world still struggle to agree on the optimal blood level or dietary dose of vitamin D, and there are questions around the accuracy of blood testing for the hormone.
"Faced with this uncertainty, you put out [recommendations] that are reasonable," he says. "Over 1800 people die of skin cancer each year, so we can't pull back on our summertime messages about sun protection. Vitamin D is important, but we can't throw the baby out with the bath water."