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Auckland University researchers are calling for compulsory addition of vitamin D to the food supply, following a new study showing large daily doses of supplements would be needed to overcome New Zealanders' chronic deficiency of the vital nutrient.
Fortification of margarine, fats and dairy foods with vitamin D is already permitted in New Zealand, but Australia has gone further and made its addition to margarine compulsory.
Vitamin D is needed for the body to absorb calcium. A deficiency can cause bone weakness, including the disease rickets. Having the optimum level of vitamin D is associated with a reduced risk of a range of conditions, including bowel cancer, high blood pressure and infectious diseases.
The Health Ministry's 2003 Food and Nutrition Guidelines say most adults, except those living in institutions, can get enough vitamin D from 15 to 30 minutes' exposure to the sun each day, but skin cancer groups warn against unprotected sun exposure.
The new study, published online in today's New Zealand Medical Journal, found that even if people significantly increased their sun exposure, their bodies would still not be producing enough vitamin D.
In summer, 88 per cent of the 201 healthy adults in the study had insufficient vitamin D in their blood, while in winter all of them had too little.
"Most Christchurch people are vitamin D deficient most of the time," the study concludes, "and a daily supplement of 2600 IU [international units] ... would correct this."
This dose is larger than that recommended on pharmacy-sold bottles and for the doctor-only prescription version, but the study says no adverse effects have been found at the much higher dosage of 10,000 IU a day.
In an editorial in the journal, Auckland University epidemiologist Associate Professor Robert Scragg and Auckland City Hospital specialist Dr Jim Bartley say mandatory fortification of foods such as margarine and milk should be considered.
"Ideally we should implement that," Professor Scragg told the Herald. "It's definitely a public health strategy we should be looking at."
International research evidence was mounting in favour of recommending supplements, particularly in winter, in the elderly and people at risk of low vitamin D, such as Maori, Pacific Islanders and south Asians.
