**4. Discussion**

With the increasing prevalence of chronic disease throughout the world and increasing interest in complementary medicine, dietary supplements have become more widely used in children [26,27]. Many varieties of dietary supplements are now marketed in China and Australia, including single-ingredient products and various combinations of vitamins, minerals, botanicals, and other constituents. Their use in healthy children is addressed towards non-clinical deficiencies, the achievement of optimal status of nutrition and health [17,28].

This study investigated the prevalence of dietary supplement use in Chinese children in mainland China and in Australia. This is the first report, to our knowledge, on the use of dietary supplements in young Chinese children under the age of five years. In this study, one fifth of Chinese children in Perth and one third of children in Chengdu and Wuhan were taking at least one nutritional supplement with no gender differences. The prevalence of dietary supplement use in young children in China was similar to that of the US (35%) and South Korea (34%), but higher than Japan (20.4%) [14–17]. However, the comparison populations in these reports generally were older children. The lower prevalence of dietary supplement use in Chinese immigrant children in Australia than children in China may be due to the age difference of the subjects. In Australia, most children were under three years old. It was found that older children in Australia were more likely to take dietary supplements.

The types of supplements commonly used in Chinese children in China and in Australia were quite different. In China, calcium and zinc supplements were most commonly used, with many children taking both. Although 58.5% of supplements users were taking calcium supplementation, the average intake was still only 131 mg per day, which is about 20% of the Adequate Intake set for calcium for Chinese children in this age group [3]. It is less than half of the calcium that can be provided from one serve (250 mL) of milk; besides milk can provide other nutrients like protein to support child growth [29]. A meta-analysis on randomized, controlled trials reported little effectiveness of calcium supplementation on bone density in healthy children, either in childhood or later life [30]. The calcium dose was of 300–1200 mg per day in 19 studies included in the meta-analysis, which was much higher than the average calcium intake from supplements in this study (131 mg in China and 105 mg in Australia). Since the level of intake of calcium supplements in China is very low, it is not possible that intake from supplements would be likely to have a positive effect on bone mineral density in Chinese children.

It has been reported in many studies that Chinese children have a low daily zinc intake [31,32]. This may be due to the higher reference value used to define the adequate daily intake in those studies. The Recommended Nutrient Intakes (RNIs) for zinc for 1–7 years old Chinese children range from 9–13.5 mg/day, which are higher than in Japan (5–7 mg/day), USA (3–5 mg/day) and in Australia (3–4 mg/day) [3,29,33,34]. The recommended intake for Chinese children is even higher than the upper level of zinc intakes for those age groups in Australia and New Zealand, which is 7 mg/day for 1–3 years and 12 mg/day for 4–8 years [33]. The 2002 China National Nutrition and Health Survey found that the median intake of zinc in 2–8 year old Chinese children ranged from 5.1 to 7.1 mg/day (the interquartile range: 3.9–9.3 mg/day), which already met the RNIs for this age group in Japan, USA and Australia [35]. However, the adequacy of zinc intake depends not only on the amount, but also its bioavailability. People consuming a diet that provides marginal zinc intake may not absorb an adequate amount of zinc if they are also consuming foods high in phytate together with high calcium [36]. The average population phytate intake of people in China (1186 mg/day) is relatively high compared to their western counterparts, but Chinese diets are low in calcium, reducing the possibility of low zinc availability [35]. The elevation of calcium intake by increasing consumption of milk is not affected by the inhibitory effect of phytate because animal sources of protein appear to promote zinc release from its phytate complex and also provides intrinsic zinc in a highly available form [36]. For young children from this study, their calcium intakes from calcium supplements were low and because of their young age, they still rely on milk products as their main calcium source. Considering the amount of zinc intake from their diet, they may not need to take zinc supplements. Together with the amount of zinc from supplements (ranging from 2.15 to 8.6 mg/day), it is a concern that some children might have reached the upper level of intakes for their age. Adverse events associated with chronic intake of supplemental zinc may include suppression of immune response, decrease in high density lipoprotein cholesterol and reduced copper status [33].

In Australia, the most popular supplements were multi-vitamins/minerals, which is consistent with previous studies in children and adolescents [16,17,37]. Fish oil supplements (42.3%) were almost as popular as multi-vitamins and minerals (46.2%). Another large sample size, cross-sectional study (*n* = 266,848) undertaken in New South Wales, Australia also reported a high prevalence of fish oil supplement use in healthy elderly people [38]. Few children were on calcium supplements in Australia. This might be due to higher consumption of milk and milk products in Australia than in China. Commercial advertising may also influence the choice of dietary supplement.

The types of dietary supplements used by young children living in China were distinct from those in Australia. This may be due to the different regulations about supplements that apply to both countries. Promotion and advertising of supplements is different in both countries. There are many reports in the literature that suggest that unnecessary or reckless use of dietary supplements can lead to problems. More studies related to the clinical effectiveness and/or safety of dietary supplements in infants and children are required, especially over the longer term. In the case of Chinese children in China, the intakes of calcium and zinc deserve special considerations in relation to development of dietary supplement regulations. Further studies on fish oil supplements in young children in Australia are also required to add to our knowledge of its health effects.

Herbal products are widely used both in China and by Chinese Australians. Most herbal traditional products not only have plant-derived materials or preparations, but may also include animal products (including scorpions, cicadas and centipedes) and mineral compounds (including cinnabar and realgar) [39]. There is a public perception that these products are inherently safe, however, the therapeutic basis of many ingredients is still not clear. Some traditional ingredients can be toxic when used for inappropriate indications, or prepared inappropriately, or used in excessive dosages, or for a prolonged duration [39–42]. It is known that some Chinese medicines can have nephrotoxicity or hepatotoxicity effects and some cause increased risk of bleeding [43–46]. There is a need to increase the awareness of toxic effects of some herbal products in the public and health care professions.

There are several limitations that need to be considered when interpreting the results of the present study. First, our results may not be representative of all Chinese children in China or in Australia because of the location of the sample and the number of subjects. Secondly, the age distribution of the subjects from two countries in this study was slightly different and this may have a small influence on the results. Nevertheless, we believe our present study to be important for understanding the present status of supplement use in Chinese pre-school children, and in monitoring future trends of supplement use.
