In general, the nutritional status of the children attending primary schools in Kuala Lumpur was good with respect to height-for-age and adequacy in several micronutrients examined. These results may be due to the socio-demographic background of the families - most parents having formal education, earning middle level income on average, and with access to affordable health care and exposure to nutrition information in the capital city of Kuala Lumpur.
The prevalence of underweight was lower than previously reported . Nearly all the children (96.6% of boys and 97.3% of girls) had normal height-for-age. A child with normal bodyweight for age is more likely to become overweight or obese if he or she is stunted; however, this was not the case in this study as the prevalence of stunting was low, at less than 5%. This finding is encouraging compared to previous studies. Zalilah et al., (2000) reported that as high as 50% of primary school children in Kuala Lumpur were stunted, in a survey of 4212 boys and 3793 girls aged 6-10 years, albeit from low income households .
This study however found a high prevalence of obesity in the young children. More than one-third of the children aged 7-12 years were overweight or obese based on BMI-for-age. This finding is higher than that reported by previous studies on children in Kuala Lumpur city. In 2002, Tee et al.,  reported that 8.4% of primary school children (n = 5,995) in Kuala Lumpur were overweight, based on the WHO 1995 definition , while Moy et al., (2004)  reported 10.1% were overweight, based on BMI-for-age >95th percentile, among 1,320 schoolchildren in the capital city. Differences in definition and criteria used by the various studies may explain some of the different results on excess adiposity in the urban children studied. Notwithstanding that, the high overweight and obesity prevalence in the present study is a matter of public health concern.
The results on iron status were encouraging since moderate to high levels of anaemia have long been one of the predominant findings of nutrition surveys among children in Malaysia [20, 21]. The biochemical results also indicated that none of the children showed deficiency of zinc, folate and vitamin B12. These findings may reflect adequacy in their dietary intake. Based on self-reported dietary history (data not shown), the intake of the children for several nutrients including protein, iron, vitamin A, thiamine, riboflavin and vitamin B12 were better than the recommended nutrient intakes (RNI) for Malaysian children .
The importance of this study is the unexpected finding of a large proportion of the children showing vitamin D deficiency (35.3%), and an almost similar proportion with insufficient vitamin D status (37.1%). We did not expect apparently healthy school children to show vitamin D deficiency, given that Kuala Lumpur is located at latitude 03° 09'N, with almost all year round of UV-B radiation of sufficient wavelength necessary for cutaneous synthesis of vitamin D. Indeed, at a recent seminar, it was revealed that cases of rickets have been presented in paediatric wards in Malaysia in recent years . There are increasing studies world-wide showing children with poor vitamin D status, including those in tropical countries [24–28].
Poor vitamin D status in children is likely to result from low dietary intake and inadequate exposure to sunshine. Unless fortified, most foods are poor sources of vitamin D, exceptions being fish oils, egg yolk, and certain types of fish and sea food. Few foods in Malaysia are fortified with vitamin D, and these are confined to some margarines and beverages only. Thus, it is not likely that children in Malaysia will obtain sufficient vitamin D from dietary sources alone.
Based on self-reported daily sunlight exposure in this study, the children also seem not to be receiving enough sun exposure, as they tend to spend more time indoor than outside the house. Moreover, indoor activity is sedentary in nature e.g. doing homework, playing computer games and watching television. Malaysians generally avoid being outdoor during the day as the weather can be very hot and humid. Moreover, parents may be concerned about safety and may not allow their children to play outside the home unaccompanied. Also, the type of clothing worn due to culture or religion may limit the capacity of the skin to synthesize vitamin D. Some of these behaviours are likely to be more evident in girls than boys, and this may explain in part the finding that more girls were deficient in vitamin D than boys. Similar findings about limited sun exposure and low dietary intake have been reported for children in tropical countries [29, 30].
Another key finding of this study is the inverse relation between vitamin D status and BMI-for-age. The boys in this study, being more obese than the girls on average, were found to have a significant negative association with vitamin D status (χ2 = 5.958; P = .016). Other studies have also shown obesity to be associated with decreased vitamin D status in children [31, 32]. Vitamin D, being fat-soluble, is readily stored in adipose tissue, and thus, it could be sequestered in the larger body pool of fat of obese individuals. As a result, there is reduced bioavailability and lower serum vitamin D concentrations [33, 34]. This has raised the concern that in obese individuals, serum 25(OH)D may not be a good indicator of vitamin D stores.
Results of poor vitamin D status amongst Malaysian school children deserve public health attention. There is the need to dispel misconceptions that low vitamin D status does not occur in a tropical country like Malaysia. Parents and teachers should be provided with information on the importance of vitamin D in the growth and development of children. In addition to helping parents make the correct dietary choices to improve vitamin D status of their children, there is a need to encourage growing children to gain adequate sun exposure through physical activity outdoors in school and at home. Public health messages and interventions must educate the population about safe sun exposure, since UV-B radiation of the same wavelength (290-315 nm) necessary to stimulate endogenous vitamin D synthesis, also contributes to skin cancers, as excess exposure causes DNA damage and skin burning.
Limitations of study
In this study, a cut off of ≤ 37.5 nmol/L was used to derive the extent of vitamin D deficiency and 37.5 - 50.0 nmol/L to indicate insufficiency. Although there is no global consensus on the biochemical definition of vitamin D deficiency, a cut-off point of ≤ 37.5 nmol/L (≤ 15 ng/mL) 25(OH)D is typically used to determine deficiency .
As the original objective of the study was to assess the micronutrient status of children, parathyroid hormone (PTH) was not determined. PTH determination should be included as a functional index of vitamin D status in future studies. It is also important to use objective measures to determine sun exposure, dietary intake and physical activity. A direct measure of fat mass, beside body mass index, may provide a more sensitive relationship between vitamin D concentration and obesity in children.