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Vitamin D deficiency in Australia and New Zealand: what are the dietary options?

Article Excerpt
Abstract

Measurement of serum vitamin D levels in population samples has revealed unexpectedly high prevalence of vitamin D deficiency among children, adults, the elderly and other vulnerable groups in Australia and New Zealand. The new Nutrient Reference Values report has established dietary recommendations for vitamin D of between 5 and 15 [micro]g/day, depending on age. Dietary intakes of vitamin D in Australia typically fall in the range of 2-3 [micro]g/day, below intakes in comparable countries. Dietary intake of vitamin D is currently dependent on consumption of a few key foods, notably margarine and oily fish. Current models of healthy eating do not deliver the recommended amounts of vitamin D and need review. Consideration should be given to the range of foods fortified with vitamin D, which is currently limited. Higher dietary intakes of vitamin D in overseas countries have been achieved through the fortification of margarine, milk and breakfast cereals. Increased voluntary fortification of dairy products with vitamin D would be a safe and simple means of increasing vitamin D intakes in Australasia in the short term. The relatively high dietary recommendation for vitamin D for elderly people cannot be met through the existing food supply and supplementation appears to be a desirable option for many.

Key words: food supply, fortified food, nutrition education, vitamin D deficiency.

INTRODUCTION

Vitamin D deficiency emerged during the industrial revolution in northern Europe and then the USA. At the beginning of the twentieth century, the vitamin D deficiency disease rickets was epidemic among urbanised young children on both sides of the Atlantic Ocean. (1) The problem in European and North American children largely subsided as the effects of sunlight on endogenous vitamin D production became understood, cod liver oil was given to children and vitamin D was isolated and added to staple foods as a public health measure in some countries. Until recently, the incidence of rickets in Australia appears to have been greatly limited by children's ready access to sunlight. (2)

Several important developments have rekindled interest in vitamin D. First, health authorities have advised the general public to reduce sun exposure and to use ultraviolet (UV)-screening skin lotions to lower the risk of skin cancer. Sunscreens with a sun protection factor (SPF) of 15 reduce the capacity of the skin to produce vitamin D by about 98%. Second, vitamin D status of communities can now be quantified through measurements of serum vitamin D, rather than by counting the cases of rickets. The Working Group of the Australian & New Zealand Bone & Mineral Society, the Endocrine Society of Australia and Osteoporosis Australia proposed that the normal serum 25-OH vitamin D concentration is over 50 nmol/L. (3) Vitamin D deficiency was defined in the following terms (amounts of serum 25-OH vitamin D): 25-50 nmol/L for mild deficiency; 12.5-25 nmol/L for moderate deficiency and <12.5 nmol/L for severe deficiency.

Third, mild vitamin D deficiency has been shown to lead to a compensatory secondary increase of parathyroid hormone; is associated with high bone turnover and is an important risk factor for osteoporosis and fractures. (4) Moderate deficiency is associated with reduced bone density, high bone turnover and increased risk of hip fracture in the elderly (5) and severe deficiency with osteomalacia in adults. Finally, noncalcaemic roles for vitamin D have been hypothesised. Some epidemiological studies have shown associations of high latitudes (less sunlight) and some cancers, type 1 diabetes and multiple sclerosis. The discovery of vitamin D receptors in most human cell types suggests a wider role for vitamin D. (6)

VITAMIN D DEFICIENCY IN AUSTRALASIA

The prevalence of vitamin D deficiency appears to be much higher in Australia and New Zealand than previously thought. (3) In a Tasmanian study conducted in winter, 68% of 16-year-old boys were found to have serum concentrations of 25-OH vitamin D less than 50 nmol/L. (7) A cross-sectional study of women with a median age of 46 years conducted in Geelong found that 43% had mild or moderate vitamin D deficiency during winter. (8) Marginal vitamin D deficiency has also been observed among younger adults in south-east Queensland. (9) In New Zealand, the recent National Children's Nutrition Survey found that 31% of children aged 5-14 years had serum 25-OH vitamin D concentrations of less than 37.5 nmol/L, with 4% less than 17.5 nmol/L. (10) Similar results were observed in adults. (11) These two studies highlight that, outside high-risk groups, mild vitamin D...

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