On 12 June a symposium titled ‘Should Australia and New Zealand allow more vitamin D into the food supply?’ was conducted in Melbourne under the auspices of the International Life Sciences Institute (ILSI). Excellent speakers outlined the current vitamin D status of Australians, the consequences of vitamin D deficiency, current dietary recommendations and intakes, and options for public health action. But are our national nutrition authorities listening?
Vitamin D recommendations
Dietary vitamin D recommendations are relatively new in Australia. After long assuming that a sunny country provided its people with adequate vitamin D, our health authorities introduced Nutrient Reference Values in 2006 in response to increasing evidence that a significant number of Australians and New Zealanders may have less than optimal (vitamin) D status. Adequate Intakes of vitamin D were considered to be 5 μg/day for children and young adults, 10 μg/day for adults aged 51-70 years and 15 μg/day for adults over 70 years of age. These recommendations mirrored those in the United States at the time.
In the United States, the Institute of Medicine recently raised the Estimated Average Requirement for vitamin D to 10 μg/day for all children and adults, with the Recommended Dietary Allowance being 15 μg/day for most groups and 20 μg/day for the elderly. The intent of these recommendations is to ensure that levels of vitamin D in the blood at the end of winter are above 50 nmol/L, which is thought to be consistent with optimal health.
A new position statement on vitamin D and health commissioned by the Australian and New Zealand Bone and Mineral Society and Osteoporosis Australia has just been published. It recommends a target blood level of above 50 nmol/L at the end of winter, consistent with the American position. In order to achieve this, recommended vitamin D intakes are 15 μg/day for children and adults and 20 μg/day for those over 70 years of age.
Vitamin D deficiency in Australia
Professor Robin Daly from Deakin University in Melbourne presented a recent national, population-based study into the prevalence of vitamin D insufficiency and deficiency in Australia. The study involved 11,247 men and women aged 25 years or over who provided a blood sample in 1999/2000 as part of the AusDiab Study. The prevalence of vitamin D deficiency (blood level <50 nmol/L) was 31%, with the prevalence in women (39%) nearly twice that of men (22% men). Non-Europeans, the elderly, the obese, the physically inactive and those with a higher level of education were at higher risk. Residents in the southern states were more at risk than those in the north. Blood vitamin D levels dropped by 17-19 nmol/L during winter compared with the peak in summer. Another recent study found similar vitamin D deficiency rates.
Professor Daly concluded that it is clear from the available evidence that vitamin D deficiency is a major problem in Australia and that there is an urgent need to identify safe and effective population-based strategies to combat it.
Implications of vitamin D deficiency
There is high level evidence indicating that vitamin D promotes absorption of calcium and phosphate from the gut, facilitates the uptake of minerals into the skeleton and is important for muscle function. Rickets, the classical childhood vitamin D deficiency disease, remains a concern among vulnerable groups in Australia. However, this ‘fast moving’ field of research has also identified associations between vitamin D status and the prevalence of many conditions and all-cause mortality. The meeting heard that most cells in the body expresses the vitamin D receptor, that many tissues outside the kidney have the capacity to make the active form of the vitamin, and that 3% of our genome is regulated by vitamin D. All this suggests that there may be many roles for vitamin D besides those relating to bone and muscle.
Increasing vitamin D in the food supply
Professor Caryl Nowson stated that Australia has one of the most restrictive food regulations in the world with respect to the amount of vitamin D permitted in the food supply. She stated that the major dietary sources of vitamin D in Australia were margarine (48%), which is fortified with vitamin D, fish (16%) and eggs (10%) but that the average estimated dietary intake for adults is only 2–3 μg/day. This is considerably less than in countries where more extensive vitamin D fortification is practised, such as Canada and the United States where average intakes range between 3–6 μg/day.
Professor Nowson argued that a modest increase in the amount of vitamin D in the food supply achieved either through mandatory fortification of key foods or voluntary fortification of a range of foods would raise dietary intakes and the population’s vitamin D status. The likely consequence would be a fall in the number of people with deficiency (<50 nmol/L) and, especially, frank deficiency (<30 nmol/L). Calcium-rich foods, such as milk, were considered ideal foods for fortification with vitamin D. Some breakfast cereals, traditionally eaten with milk, are fortified with vitamin D in the United States and the United Kingdom.
Draft Dietary Guidelines: a vitamin D void
When I read the draft Australian Dietary Guidelines I expected to find at least a brief review of Australia’s vitamin D deficiency problem, recommendations on how it could be addressed in the context of the current food supply and prospects for future action. But don’t bother looking – there wasn’t a single literature review conducted on vitamin D and any aspect of health. Vitamin D is hardly mentioned in the text of the report – page 7 states Deficiency in some nutrients such as … vitamin D is also of concern for some Australians and there are subsequent brief statements that fish and dairy products contain vitamin D, but that’s it.
Perhaps we should be thankful for small mercies. When the initial dietary modelling for the Dietary Guidelines was circulated for comment the authorities stated that vitamin D deficiency was an issue but then proceeded to limit ALL major dietary sources of the vitamin – margarine, fish, eggs and even dairy products, the latter three on environmental grounds. After howls of protest these constraints were relaxed somewhat but restrictions on margarine remained and there were no recommendations about vitamin D-fortified milk. None of the ‘foundation diets’ in the final dietary modelling contained 5 μg of vitamin D, let alone the higher intakes now being recommended. In fact, these ‘healthy’ diets provided no more vitamin D than adults currently consume in self-selected diets. The original dietary modelling document stated that the failure of these diets to meet the Nutrient Reference Values for vitamin D would be addressed later, but it wasn’t.
So it appears that the only prospect for addressing Australia’s vitamin D deficiency in the short- or medium-term will be voluntary actions by sections of the food industry. Where is the leadership from our national nutrition authorities on this issue of national importance?