The majority (87%) of East African immigrant children and adolescents in this study were vitamin D deficient or insufficient. The associated pattern of risk factors for VDD (younger age, female gender/covering clothing, residence in Australia for a longer time, decreased daylight exposure, and vitamin D level tested in winter or spring) indicates a reduction in exposure to UVR in affected individuals.10,11,12,13,18,22,23,24,25,26,27,28,29
The city of Melbourne is at significantly higher latitude than the countries of origin of this population. In Boston (latitude 42° North), Caucasian adults had minimal pre‐vitamin D production during winter.10
This study documents the compounding effect of risk factors for VDD on the seasonal variation in vitamin D production in a population of dark skinned children in Melbourne, suggesting that inadequate endogenous production of vitamin D is the main cause of VDD in this group. These risk factors lead to worsening VDD with time spent in Australia. Public health campaigns designed to prevent solar skin damage and cancer through reduced exposure to UVR need to consider the public health implications of their intervention for population subgroups at risk of VDD.6
Although VDD was asymptomatic in our subjects, there is evidence of biological consequences in some children. One quarter of children tested had elevated PTH levels with VDD or VDI, and half of the children with VDD who had radiographs, had abnormal results. In Finnish adolescents, VDD was associated with increased PTH levels and decreased bone mineral accumulation over time.28,29
Peak bone mass, an important factor in osteoporosis fracture risk, is mostly attained by late adolescence.30
Suboptimal vitamin D status in children and adolescents may affect the attainment of peak bone mass and increase the risk of osteoporosis and fractures later in life.
Significant levels of VDD have been documented in dark skinned pregnant women in Melbourne and veiled pregnant women living in Melbourne and in the Middle East.8,14,31
We observed that 65% of females aged 10 years or more had VDD. Cultural factors such as covering clothing limit sun exposure in young women from this background. Our findings of an increased rate of covering clothing and limitation of sun exposure in older females indicates that these risk factors for VDD are likely to persist throughout adolescence into the child‐bearing years. VDD in adolescent females, therefore, increases the risk of VDD, hypocalcaemia and rickets in future offspring.32
Our finding that a younger age (less than 5 years) is a risk factor for VDD may indicate decreased vitamin D stores in this age group, possibly as a result of maternal VDD, prolonged breastfeeding and/or increased vitamin D requirements at a time of increased skeletal growth. Establishing an awareness of VDD and a cultural tolerance of vitamin D supplementation in children and adolescents at risk of VDD is an important ongoing public health intervention in the prevention of VDD in current and future generations.
The serum level of 25‐OHD required for appropriate skeletal growth in childhood is debated.33
Seasonal vitamin D supplementation increases calcitriol levels and suppresses PTH levels in Spanish children with 25‐OHD levels <30 nmol/l,34
suggesting that 25‐OHD levels below 30 nmol/l are clinically important in children. We found a number of children with 25‐OHD levels between 25 and 36 nmol/l who had elevated PTH levels. This supports the proposal that the target 25‐OHD level should be higher than 25 nmol/l.34,35
Although we found no associated biochemical or radiological abnormalities in children with 25‐OHD levels above 36 nmol/l, we will continue to consider 25‐OHD levels less than 50 nmol/l (20 ng/ml) to be abnormally low, until there are data to prove that lower levels are safe.
We found a high prevalence of anaemia (20%) and iron deficiency (19%) in this population, and higher rates of anaemia (39%) and iron deficiency (35%) in children aged less than 5 years, comparable with another group of African refugee children.36
Using WHO criteria, the level of anaemia in this population is a “moderate” public health problem.21
In contrast, the prevalence of anaemia (1.1%) in young Australian children of mixed origin37
is not a public health problem, while the prevalence in Tanzanian preschool children (84%) and school children (55–67%)38,39
is considered a severe public health problem by WHO criteria. In data published elsewhere, we have not been able to demonstrate an association between anaemia and intestinal parasite infestation in children from this study.40
Although malaria was not suspected in any subject, asymptomatic malarial parasitaemia may explain some cases of anaemia in children from this background living in Australia41
and we have subsequently added screening to our clinic protocol. Routine assessment of immigrant children from developing countries should, therefore, include screening for anaemia, iron deficiency and malarial parasitaemia, especially when these conditions are prevalent in the country of origin.
Our finding that 20% of children were vitamin A deficient is concerning, given the morbidity and mortality risks associated with mild vitamin A deficiency.42,43
We are surprised that vitamin A deficiency is prevalent in children who spent time in refugee camps, as vitamin A supplementation is routine in many camps. A treatment strategy would be to provide routine vitamin A supplements to immigrant children from countries where vitamin A deficiency is prevalent. We can not explain the association of vitamin A deficiency with VDD.
Overall, 5% of children were overweight and the risk of being overweight was associated with better educational levels in the child's carer. We did not collect other data describing socio‐economic status. This group of immigrant children may be at risk of obesity given the increasing prevalence of obesity in Australian children.44
We recommend that all dark skinned children and adolescents who migrate to higher latitudes, or who wear covering clothing, have their vitamin D status assessed. We are concentrating on a cheap, high‐dose intermittent cholecalciferol liquid supplement in an olive oil base as vitamin D supplementation for the treatment and prevention of VDD in these children. We have concerns about compliance with daily dose regimes in marginalised communities living in Australia.45
The high prevalence of VDD in this immigrant population has implications for a wider population of children, defined generically by having increased skin pigmentation and living at higher latitudes, or by wearing covering clothing. Better data are needed to document the prevalence of VDD in different population subgroups defined in this way.
What is already known on this topic
- Endogenous production of 25‐hydroxyvitamin D is determined by exposure of human skin to UVB radiation and skin pigmentation.
- Suboptimal vitamin D status in children and adolescents may affect the attainment of peak bone mass and increase the risk of osteoporosis later in life.
- Known risk factors for vitamin D deficiency in children include winter season, immigrant or refugee status, skin pigmentation, atmospheric pollution and geographical latitude.
What this study adds
- This prospective study identifies a high prevalence of vitamin D deficiency and a number of measurable risk factors in a large cohort of East African immigrant children and adolescents.
- This study documents the interaction between seasonal variation in UVB radiation and socio‐cultural factors limiting exposure to sunlight in this population.
- This will assist in the planning of public health interventions in populations at risk of vitamin D deficiency as defined by the known risk factors.