Despite recommendations from Health Canada7
and the Canadian Paediatric Society,8
there has been a failure to prevent vitamin D deficiency in Canada, resulting in clinically important skeletal and systemic morbidity and an overall annual incidence rate of vitamin D–deficiency rickets of 2.9 per 100 000 children. This condition was most frequently observed among darker-skinned, breast-fed infants and children, with the highest incidence among children from north (Yukon Territory, Northwest Territories and Nunavut). Maternal characteristics (skin colour, lack of sun exposure and inadequate vitamin D intake or supplementation) were contributing factors.
Rickets in children has been identified as a persistent global health concern largely through published case series, retrospective chart reviews at local institutions and cross-sectional studies.1,4,15–18
Recent reports have noted cases not only from regions with more limited sunshine, such as New Zealand,19
the United Kingdom20
and the United States,18
but also from sunnier regions such as Africa,21
Lack of sunlight exposure (even at low latitudes), breast-feeding, darker skin and recent immigration are the most common risk factors in these reports. In the United Kingdom (West Midlands), Callaghan and colleagues, in a prospective surveillance study lasting 1 year, found an overall vitamin D deficiency annual incidence rate of 7.5 per 100 000 children, with children of black African or African–Caribbean ethnic background having the highest incidence rates.23
As in our study, the north–south gradient has been shown to be a factor, with more Asian children living in northern Scotland than in southern Scotland having rickets.24
The question has been raised whether rickets has re-emerged in recent years, or whether it has simply remained a persistent problem. In Canada, studies of the systematic prevalence and incidence have not been performed in the same regions at different times. The available evidence suggests that, like observations worldwide, rickets has continued to be an important child health issue in Canada despite simple measures for its prevention.
Breast milk is indisputably the ideal food for infants; however, breast milk typically contains about 25 IU or less vitamin D per litre,6,25
which is insufficient for rickets prevention. Although there is evidence that limited sun exposure may prevent rickets in some breast-fed infants,26,27
concern over the health risks of sun exposure have led to the recommendation that all breast-fed infants receive supplemental vitamin D (400 IU/d).7,8
It is recommended that breast-fed infants who reside above the 55th latitude in Canada or in areas at lower latitudes that have a high incidence of vitamin D deficiency receive 800 IU/d during the winter months.28
In our study, there were no reported cases of rickets among children who were breast-fed and received regular vitamin D (400 IU/d). Our findings suggest that the current guidelines for rickets prevention can be effective but that they are not consistently being implemented.
Babies who drink an adequate amount of infant formula to achieve normal growth typically receive sufficient vitamin D (400 IU per litre of standard commercial formula) to prevent rickets. In our study, however, 3 infants who received enough infant formula to support normal growth manifested rickets in the first few weeks of life. The timing of presentation of these cases suggests that the vitamin D deficiency resulted from insufficient transfer of 25-hydroxyvitamin D from the mother to the fetus (which mostly occurs during the third trimester)29,30
and that the deficit was too severe to be rescued by vitamin D–fortified formula. These observations underline the importance of maternal vitamin D intake during pregnancy (for both breast-and bottle-fed infants) and lactation (for breast-fed infants). In a review of vitamin intake during pregnancy,31
Hollis and Wagner proposed that the current guidelines for expectant mothers (200–400 IU/d, 800 IU/d above the 55th latitude)6,14
may be grossly inadequate, a hypothesis that is being investigated in clinical trials.
The main limitation of our study is that the monthly surveys were sent only to pediatricians and pediatric subspecialists, but not to family physicians. Vitamin D–deficiency rickets is a condition that can be diagnosed and treated by family doctors, many of whom work in remote regions of Canada. If family physicians had been included, the incidence of rickets would undoubtedly have been increased. In addition, the mean response rate of 85%, although higher than for most mail-out surveys published in medical journals,32
may have also decreased the number of cases identified.
Given the failure to prevent vitamin D–deficiency rickets in Canada and the potential for serious morbidity, there is an urgent need for heightened awareness among health care providers and the general public. Attention to maternal vitamin D status during pregnancy and lactation, assessment of the lack of success associated with the implementation of current recommendations and re-evaluation of the current guidelines in high-risk populations (darker-skinned, northern and indigenous mothers and infants) are warranted.
@ See related article page 169