Influence of ethnicity on biochemical markers of health and disease in the CALIPER cohort of healthy children and adolescents

Background Accurate pediatric reference intervals (RIs) for laboratory tests determined in a healthy pediatric population are essential for correct laboratory test interpretation and clinical decision-making. In pediatrics, RIs require partitioning by age and/or sex; however, the need for partitioning based on ethnicity is unclear. Here, we assessed the influence of ethnicity on biomarker concentrations in the Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER) cohort of healthy children and adolescents and compared the results with the National Health and Nutrition Examination Survey (NHANES). Methods A total of 52 biomarkers were measured in a multiethnic population of 846-1179 healthy children (aged 5 to <19 years) upon informed consent. Biomarker concentrations were retrospectively compared between four major ethnic groups (i.e. Black, Caucasian, East Asian, and South Asian, determined by parental ethnicity). Retrospective results were verified prospectively using an additional 500 healthy pediatric samples with equal sample size across ethnicities. Ethnic-specific differences were assessed based on statistical significance and biological and analytical variations. Appropriate age-, sex-, and ethnic-specific RIs were calculated. Results Ethnic-specific differences were not observed for 34 biomarkers examined in the retrospective analysis, while 18 demonstrated statistically significant ethnic differences. Among these, seven analytes demonstrated ethnic-specific differences in the prospective analysis: vitamin D, amylase, ferritin, follicle-stimulating hormone (FSH), immunoglobulin A (IgA), immunoglobulin G (IgG), and immunoglobulin M (IgM). Analysis of select NHANES data confirmed CALIPER findings. Conclusions This is the first comprehensive Canadian pediatric study examining ethnic-specific differences in common biomarkers. While the majority of biomarkers did not require ethnic partitioning, ethnic-specific RIs were established for seven biomarkers showing marked differences. Further studies in other populations are needed to confirm our findings.

Vitamin D sufficiency, a serum 25-hydroxyvitamin D at least 30 ng/mL reduced risk for adverse clinical outcomes in patients with COVID-19 infection

Background

To investigate the association between serum 25-hydroxyvitamin D levels and its effect on adverse clinical outcomes, and parameters of immune function and mortality due to a SARS-CoV-2 infection.

Study design

The hospital data of 235 patients infected with COVID-19 were analyzed.

Results

Based on CDC criteria, among our study patients, 74% had severe COVID-19 infection and 32.8% were vitamin D sufficient. After adjusting for confounding factors, there was a significant association between vitamin D sufficiency and reduction in clinical severity, inpatient mortality serum levels of C-reactive protein (CRP) and an increase in lymphocyte percentage. Only 9.7% of patients older than 40 years who were vitamin D sufficient succumbed to the infection compared to 20% who had a circulating level of 25(OH)D< 30 ng/ml. The significant reduction in serum CRP, an inflammatory marker, along with increased lymphocytes percentage suggest that vitamin D sufficiency also may help modulate the immune response possibly by reducing risk for cytokine storm in response to this viral infection.

Conclusion

Therefore, it is recommended that improving vitamin D status in the general population and in particular hospitalized patients has a potential benefit in reducing the severity of morbidities and mortality associated with acquiring COVID-19.

Effect of vitamin D supplementation on free and total vitamin D: A comparison of Asians and Caucasians

OBJECTIVES

It is well established that UK Asians typically have lower vitamin D levels than Caucasians. It is also known that vitamin D binding protein (DBP) is lower in some races than Caucasians. To investigate how ethnicity, skin colour and genetic variation affect the response to vitamin D (15000 IU) administered to young Asian and Caucasian men.

DESIGN

Prospective, single-centre clinical trial.

PARTICIPANTS

Sixty young men (18-25 year) of Asian (n = 30) and Caucasian (n = 30) origin.

MEASUREMENTS

We measured serum calcium, phosphate, magnesium, alkaline phosphatase, albumin, parathyroid hormone; total 25 hydroxyvitamin D (25OHD); calculated and directly measured free 25OHD; DBP at baseline and 4 weeks; DBP genotype, skin colour (Fitzpatrick scale), dietary vitamin D and calcium intake at baseline; and urine calcium:creatinine ratio at baseline, 1 and 4 weeks.

RESULTS

At baseline, Asians had lower serum total 25OHD (26.4 [13.7] vs 34.1 [12.3] nmol/L P = 0.0272) and DBP (6.7 [3.4] vs 9.6 [4.4] nmol/L; P = 0.0065) but similar free 25OHD (16.7 [10.4] vs 17.8 [7.5] pmol/L P = 0.6530). After dosing, total 25OHD rose similarly in each group (≈56 nmol/L), but measured free 25OHD rose more in Asians (18.1 [9.4] vs 12.2 [13.3] pmol/L P = 0.0464). Lower DBP at baseline, possibly reflecting genotype differences, was associated with a greater change in measured free 25OHD in Caucasians, but not in Asians.

CONCLUSIONS

Asian compared with Caucasian males had a larger increment in measured free 25OHD following 150 000 units vitamin D3, possibly reflecting differences in DBP affinity for 25OHD. Ethnicity should be considered when devising guidelines for the treatment of vitamin D deficiency.

Vitamin D assays and the definition of hypovitaminosis D: results from the First International Conference on Controversies in Vitamin D

The First International Conference on Controversies in Vitamin D was held in Pisa, Italy, 14-16 June 2017. The meeting's purpose was to address controversies in vitamin D research, review the data available, to help resolve them, and suggest a research agenda to clarify areas of uncertainty. The serum 25-hydroxyvitamin D [25(OH)D] concentration [i.e. the sum of 25(OH)D3 and 25(OH)D2 ] remains the critical measurement for defining vitamin D status. Assay variation for 25(OH)D has contributed to the current chaos surrounding efforts to define hypovitaminosis D. An essential requirement to develop a consensus on vitamin D status is that measurement of 25(OH)D and, in the future, other potential vitamin D biomarkers [e.g. 1α,25(OH)2 D3 , 3-epi-25(OH)D, 24,25(OH)2 D3, vitamin D-binding protein, free/bioavailable 25(OH)D and parathyroid hormone] be standardized/harmonized, to allow pooling of research data. Vitamin D Standardization Program tools are described and recommended for standardizing 25(OH)D measurement in research. In the future, similar methodology, based on National Institute for Standards and Technology standard reference materials, must be developed for other candidate markers of vitamin D status. Failure to standardize/harmonize vitamin D metabolite measurements is destined to promulgate continued chaos. At this time, 25(OH)D values below 12 ng ml-1 (30 nmol l-1 ) should be considered to be associated with an increased risk of rickets/osteomalacia, whereas 25(OH)D concentrations between 20 ng ml-1 and 50 ng ml-1 (50-125 nmol l-1 ) appear to be safe and sufficient in the general population for skeletal health. In an effort to bridge knowledge gaps in defining hypovitaminosis D, an international study on rickets as a multifactorial disease is proposed.

Vitamin D status in relation to physical performance, falls and fractures in the Longitudinal Aging Study Amsterdam: A reanalysis of previous findings using standardized serum 25-hydroxyvitamin D values

The Longitudinal Aging Study Amsterdam (LASA) is an ongoing prospective cohort study in a representative sample of Dutch older persons. In previous LASA studies, lower serum 25-hydroxyvitamin D (25(OH)D) values, as assessed by a competitive protein binding assay or radioimmunoassay, have been associated with decreased physical functioning, falls and fractures. Recently, serum 25(OHD) values in LASA were standardized using the Vitamin D Standardization Program (VDSP) protocol as part of the European ODIN project. In the current manuscript, the influence of standardizing serum 25(OH)D values will be discussed using the associations with physical functioning, falls and fractures as examples.

Vitamin D and food allergies in children: A systematic review and meta-analysis

BACKGROUND

Vitamin D insufficiency has been associated with immune dysfunction and linked to the epidemic of atopic diseases in the Western hemisphere, yet there are studies with conflicting results, and the risk has not been quantified uniformly across studies.

OBJECTIVE

To perform a systematic review and meta-analysis to evaluate and quantify if vitamin D deficiency is associated with the presence and persistence of food allergy.

METHODS

A systematic review was undertaken to assess for the association between food allergy and vitamin D status in children.

RESULTS

A total of 368 citations relevant to this systematic review were identified. In the whole review, 5105 children were included. We did not find a significant association between 25 hydroxy vitamin D (25(OH)D) status and risk of food allergy in children (odds ratio [OR] 1.35 [95% confidence interval {CI}, 0.79-2.29]; p = 0.27, I2 = 58.3%). We conducted subgroup analyses based on different cutoffs of the 25(OH)D status (20 versus 30 ng/mL). Only one study used 30 ng/mL and found that children with <30 ng/mL were more likely to report food allergy than children with a 25(OH)D status of ≥30 ng/mL (OR 2.04 [95% CI, 1.02-4.04]; p = 0.04). Four studies compared children with a 25(OH)D status of <20 ng/mL to children with a 25(OH)D status of ≥20 ng/mL and found no significant differences (OR 1.18 [95% CI, 0.62-2.27]; p = 0.62, I2 = 62.7%).

CONCLUSION

Based on the studies analyzed, this systematic review did not identify a significant association between vitamin D status and food allergy. Interpretation of the included studies was limited by a lack of a standard definition for vitamin D deficiency and insufficient knowledge regarding the optimal vitamin D status needed to impact immune function. Longitudinal studies are warranted to assess if vitamin D might contribute to the development of food allergy.

Vitamin D and mortality: Individual participant data meta-analysis of standardized 25-hydroxyvitamin D in 26916 individuals from a European consortium

Background

Vitamin D deficiency may be a risk factor for mortality but previous meta-analyses lacked standardization of laboratory methods for 25-hydroxyvitamin D (25[OH]D) concentrations and used aggregate data instead of individual participant data (IPD). We therefore performed an IPD meta-analysis on the association between standardized serum 25(OH)D and mortality.

Methods

In a European consortium of eight prospective studies, including seven general population cohorts, we used the Vitamin D Standardization Program (VDSP) protocols to standardize 25(OH)D data. Meta-analyses using a one step procedure on IPD were performed to study associations of 25(OH)D with all-cause mortality as the primary outcome, and with cardiovascular and cancer mortality as secondary outcomes. This meta-analysis is registered at ClinicalTrials.gov, number NCT02438488.

Findings

We analysed 26916 study participants (median age 61.6 years, 58% females) with a median 25(OH)D concentration of 53.8 nmol/L. During a median follow-up time of 10.5 years, 6802 persons died. Compared to participants with 25(OH)D concentrations of 75 to 99.99 nmol/L, the adjusted hazard ratios (with 95% confidence interval) for mortality in the 25(OH)D groups with 40 to 49.99, 30 to 39.99, and <30 nmol/L were 1.15 (1.00–1.29), 1.33 (1.16–1.51), and 1.67 (1.44–1.89), respectively. We observed similar results for cardiovascular mortality, but there was no significant linear association between 25(OH)D and cancer mortality. There was also no significantly increased mortality risk at high 25(OH)D levels up to 125 nmol/L.

Interpretation

In the first IPD meta-analysis using standardized measurements of 25(OH)D we observed an association between low 25(OH)D and increased risk of all-cause mortality. It is of public health interest to evaluate whether treatment of vitamin D deficiency prevents premature deaths.

Developing vitamin D dietary guidelines and the lack of 25-hydroxyvitamin D assay standardization: The ever-present past

Unstandardized laboratory measurement of 25-hydroxyvitamin D (25(OH)D) confounds efforts to develop clinical and public health vitamin D guidelines. The Vitamin D Standardization Program (VDSP), an international collaborative effort, was founded in 2010 to correct this problem. Nearly all published vitamin D research is based on unstandardized laboratory 25(OH)D measurements. While it is impossible to standardize all old data, it may be possible to identify a small subset of prior studies critical to guidelines development. Once identified it may be possible to calibrate their 25(OH)D values to the NIST and Ghent University reference measurement procedures using VDSP methods thereby permitting future guidelines to be based on standardized results. We simulated the calibration of a small set of ten clinical trials of vitamin D supplementation on achieved 25(OH)D under minimal sun exposure. These studies were selected because they played a prominent role in setting the 2010 vitamin D dietary reference intakes (DRI). Using random-effects meta-regression analysis, Vitamin D External Quality Assessment (DEQAS) data on assay bias was used to simulate the potential bias due to the lack of assay standardization by calibrating the achieved 25(OH)D levels from those 10 studies to: (1) the largest negative, and (2) the largest positive bias from the DEQAS all laboratory trimmed mean (ALTM) for the appropriate assay and year of analysis. For a usual vitamin D intake of 600IU/day the difference in mean achieved 25(OH)D values for those two options was 20nmol/L. However, without re-calibration of 25(OH)D values it is impossible to know the degree to which any of the current guidelines may have been biased. This approach may help stimulate the search for and standardization of that small subset of key studies and, in the cases where standardization is impossible, to identify areas of urgently needed vitamin D research.

An update on vitamin D deficiency and at risk groups

Vitamin D is required for healthy bones. We need sunlight and good renal and liver function for the synthesis of vitamin D, although it can also be taken in diet. Severe deficiency causes the bone diseases rickets and osteomalacia. Supplementation with vitamin D can help prevent low birth weight and non-vertebral fractures. Roles for vitamin D in other aspects of health are controversial.

[Nutritional guidelines for healthy children aged 1-3 years - Polish Expert Group statement. Part I- energy and nutritional components demand]

Updating of the nutritional guidelines for the Polish population requires updates of the nutritional norms for children. We present the Polish Expert Group statement (2012) on intake of selected nutrients (protein, lipids, carbohydrates, vitamin D and E) essential in nutrition of children aged 1-3 years. For this purpose the Expert Group reviewed available scientific data: the recent guidelines, nutritional norms and recommendations, systematic reviews and expert opinions as well as original publications, in relation to the specific requirements of the Polish population.

Development and certification of a standard reference material for vitamin D metabolites in human serum

The National Institute of Standards and Technology (NIST), in collaboration with the National Institutes of Health's Office of Dietary Supplements (NIH-ODS), has developed a Standard Reference Material (SRM) for the determination of 25-hydroxyvitamin D [25(OH)D] in serum. SRM 972 Vitamin D in Human Serum consists of four serum pools with different levels of vitamin D metabolites and has certified and reference values for 25(OH)D(2), 25(OH)D(3), and 3-epi-25(OH)D(3). Value assignment of this SRM was accomplished using a combination of three isotope-dilution mass spectrometry approaches, with measurements performed at NIST and at the Centers for Disease Control and Prevention (CDC). Chromatographic resolution of the 3-epimer of 25(OH)D(3) proved to be essential for accurate determination of the metabolites.

Measurement of 25-hydroxyvitamin D in the clinical laboratory: current procedures, performance characteristics and limitations

In this review we describe procedures, performance characteristics and limitations of methods available for the measurement of 25-hydroxyvitamin (25OHD) since the year 2000. The two main types of methods are competitive immunoassay and those based on chromatographic separation followed by non-immunological direct detection (HPLC, LC-MS/MS). Lack of a reference standard for 25OHD has, until recently, been a major issue resulting in poor between-method comparability. Fortunately this should soon improve due to the recent introduction of a standard reference material in human serum (SRM 972) from the National Institute of Standards and Technology (NIST). For immunoassay, specificity can be an issue especially in relation to the proportion of 25OHD2 that is quantified whereas HPLC and LC-MS/MS methods are able to measure the two major vitamin D metabolites 25OHD2 and 25OHD3 independently. HPLC and LC-MS/MS require more expensive equipment and expert staff but this can be offset against lower reagent costs. Increasingly procedures are being developed to semi-automate or automate HPLC and LC-MS/MS but run times remain considerably longer than for immunoassays especially if performed on automated platforms. For most HPLC and LC-MS/MS methods extraction and procedural losses are corrected for by the inclusion of an internal standard which, in part, may account for higher results compared to immunoassay. In general precision of immunoassay, HPLC and LC-MS/MS are comparable and all have the required sensitivity to identify severe vitamin D deficiency. Looking to the future it is hoped that the imminent introduction of a standard reference method (or methods) for 25OHD will further accelerate improvements in between method comparability.

Infant feeding practices and associated factors in the first six months of life: the Norwegian infant nutrition survey

AIM

To describe and evaluate infant feeding practices during the first 6 mo of life in relation to recommendations, and to study infant feeding practices in relation to maternal and infant characteristics.

METHODS

Data from 2383 Norwegian infants aged 6 mo were collected by a self-administered semi-quantitative food-frequency questionnaire measuring feeding practices at 6 mo and feeding practices retrospectively at < or = 5.5 mo of age.

RESULTS

Only 1% of the infants had never been breastfed. The proportion of breastfed infants was 96% at 1 mo, 85% at 4 mo and 80% at 6 mo. The proportion of exclusively breastfed infants was 90% at 1 mo, 44% at 4 mo and 7% at 6 mo. Twenty-one percent of the infants were introduced to solid foods before the age of 4 mo. For exclusive breastfeeding at 4 mo, breastfeeding at 6 mo and timely introduction of solid foods (not before 4 mo) significant positive trends were found for maternal age, education and degree of urbanization. Negative associations were found for maternal smoking. Furthermore, exclusive breastfeeding at 4 mo was associated with infant gender and marital status, and the odds of breastfeeding at 6 mo significantly decreased with decreasing infant birthweight. Finally, both the odds of exclusive breastfeeding at 4 mo and of breastfeeding at 6 mo increased with increasing numbers of children.

CONCLUSION

These results indicate that a majority of Norwegian infants are fed in accordance with infant feeding recommendations during their first 6mo of life. However, the duration of exclusive breastfeeding is shorter than recommended. Infant feeding practices are significantly associated with maternal and infant characteristics.

Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety

For adults, the 5-microg (200 IU) vitamin D recommended dietary allowance may prevent osteomalacia in the absence of sunlight, but more is needed to help prevent osteoporosis and secondary hyperparathyroidism. Other benefits of vitamin D supplementation are implicated epidemiologically: prevention of some cancers, osteoarthritis progression, multiple sclerosis, and hypertension. Total-body sun exposure easily provides the equivalent of 250 microg (10000 IU) vitamin D/d, suggesting that this is a physiologic limit. Sailors in US submarines are deprived of environmentally acquired vitamin D equivalent to 20-50 microg (800-2000 IU)/d. The assembled data from many vitamin D supplementation studies reveal a curve for vitamin D dose versus serum 25-hydroxyvitamin D [25(OH)D] response that is surprisingly flat up to 250 microg (10000 IU) vitamin D/d. To ensure that serum 25(OH)D concentrations exceed 100 nmol/L, a total vitamin D supply of 100 microg (4000 IU)/d is required. Except in those with conditions causing hypersensitivity, there is no evidence of adverse effects with serum 25(OH)D concentrations <140 nmol/L, which require a total vitamin D supply of 250 microg (10000 IU)/d to attain. Published cases of vitamin D toxicity with hypercalcemia, for which the 25(OH)D concentration and vitamin D dose are known, all involve intake of > or = 1000 microg (40000 IU)/d. Because vitamin D is potentially toxic, intake of >25 microg (1000 IU)/d has been avoided even though the weight of evidence shows that the currently accepted, no observed adverse effect limit of 50 microg (2000 IU)/d is too low by at least 5-fold.

Medical devices; reclassification and codification of vitamin D test system--FDA. Final rule

The Food and Drug Administration (FDA) is announcing that it has issued an order in the form of a letter to INCSTAR Corp. reclassifying INCSTAR 25-Hydroxyvitamin D 125I Radioimmunoassay (RIA). This radioimmunoassay device is intended for use in clinical laboratories for the quantitative determination of 25-hydroxyvitamin D (25-OH-D) and other hydroxylated metabolites of vitamin D in serum or plasma to be used in the assessment of vitamin D sufficiency. The device and substantially equivalent devices of this generic type were reclassified from class III (premarket approval) to class II (special controls). Accordingly, the order is being codified in the Code of Federal Regulations.

Evaluation of multiple micronutrient supplementation in the management of oral submucous fibrosis in Karachi, Pakistan

Oral submucous fibrosis (OSF) is an oral precancerous condition characterized by symptoms such as intolerance to spicy food, altered salivation, progressive difficulty in opening the mouth, and signs like vesiculation, ulceration, blanching, rigidity, and stiffening of the oral mucosa and depapillation and altered mobility of the tongue. It is seen mostly among people of Indian subcontinent origin. The major structural change is extensive fibroelastic scarring of the lamina propria and deeper connective tissues. A combination of micronutrients (vitamins A, B complex, C, D, and E) and minerals (iron, calcium, copper, zinc, magnesium, and others) was evaluated for its efficacy in controlling the symptoms and signs of OSF in 117 compliant subjects in Karachi, Pakistan, in a single-arm preliminary study. The subjects received supplementation for one to three years. Significant improvement in symptoms, notably intolerance to spicy food, burning sensation, and mouth opening, was observed at exit. The interincisor distance deteriorated in 11 subjects (10%) at exit; it was stable in 56 subjects (49%) and improved in 48 (41%). The mean interincisor distance was 19.1 +/- 10.8 (SD) mm at exit compared with 16.2 +/- 7.5 mm at baseline. A significant proportion of concomitant lesions like leukoplakia also regressed at exit. The major outcome from this study was a beneficial clinical response in subjects with OSF to multiple micronutrient intervention, which justifies its further evaluation in well-designed randomized controlled trials in other settings in South Asia.

Vitamin D adequacy: a possible relationship to breast cancer

(1) Low levels of dietary calcium and vitamin D, biochemically interrelated, increase the promoting action of high dietary fat on chemically induced mammary carcinogenesis in animal studies. (2) High dietary fat increases mammary epithelial cell proliferation, particularly the "hormonally driven" hyperproliferation during breast growth and development in young animals. Increased dietary calcium (and probably vitamin D) lessens the increase of proliferation induced by high fat. These data, although limited, suggest that the maximum effect of diet (high fat increase, as well as calcium and vitamin D modulation) on eventual breast cancer may be during puberty, and adolescence, when the mammary gland is actively growing and developing. (3) An inverse epidemiological correlation has been developed between sunlight availability as a source of vitamin D and the risk of breast cancer in the U.S. and Canada. (4) Current vitamin D and calcium dietary intake in the U.S. is far below the RDA in all female age groups, particularly for the elderly. (5) Reduction of breast cancer risk, and simultaneously osteoporosis, might be achieved by increasing dietary intake of calcium and vitamin D to RDA levels. This may be particularly applicable to females during puberty and adolescence.

Vitamin D and breast cancer

1. 1,25-Dihydroxyvitamin D3, the biologically active form of vitamin D, in addition to regulating calcium homeostasis, also has antiproliferative and prodifferentiating effects. 2. Most studies concerning the therapeutic potential of analogs of 1,25(OH)2D3, which are antiproliferative and prodifferentiating but do not cause hypercalcemia, have been done using leukemic cells. 3. Recent evidence from both in vivo and in vitro studies has indicated that 1,25(OH)2D3 or analogs of 1,25(OH)2D3 can inhibit the growth of breast cancer cells, thus suggesting the therapeutic potential of analogs of 1,25(OH)2D3 in the treatment of breast cancer.

Reversion of the steroid-induced decrease of serum osteocalcin with sodium fluoride

Osteopenia observed in corticotherapy is due, among other causes, to a decrease in bone formation as can be shown by a steroid-induced osteocalcin decrease. Although various treatments have been proposed there is no agreement as to which one is the best. Two such treatments, sodium fluoride and vitamin D administration increase osteocalcin levels. We treated a group of 12 patients under corticoid therapy (mean dose 16 mg per day) with 50 mg/day p.o. sodium fluoride, and determined osteocalcin levels before and two weeks after sodium fluoride treatment. Similarly, another group of 9 patients with a similar mean steroid dose was treated with 0.5 micrograms/day of 1 alpha (OH)2D3 in order to assess the effect of this vitamin on osteocalcin and to determine which was the best treatment. Both groups were compared with respective control groups. A significant osteocalcin increase was observed in the control groups (p less than 0.001); similar significance was observed in the sodium fluoride group, whereas a lower significance (p less than 0.01) was observed in the vitamin D group. These results suggest that sodium fluoride could be more effective than vitamin D in the treatment of steroid-induced osteopenia.

Vitamin D status, parathyroid hormone and sunlight in Turkish, Moroccan and Caucasian children in The Netherlands

At the end of the winter circulating concentrations of 25-hydroxyvitamin D (25-OHD) in Asian and Mediterranean immigrants in northwestern European countries are usually very low. This may lead to vitamin D deficiency and eventually to rickets. Children are more prone to develop vitamin D deficiency. The vitamin D status of 8-year-old Turkish, Moroccan and Caucasian children was assessed by measuring plasma concentrations of 25-OHD and parathyroid hormone (PTH) and related to the cumulated global sun radiation (CGSR). The study population was selected from school children in The Hague and Rotterdam (The Netherlands). In each city blood samples were examined from 40 migrant children and a Caucasian reference group (n = 40) (matched for age and sex). Children in The Hague were examined at the end of the winter and early spring (February/April) and those in Rotterdam in late spring and early summer (May/June). Mean plasma 25-OHD concentrations for the migrant children in both cities were significantly lower than for the Caucasian reference group. The lowest 25-OHD values were measured in migrant children in The Hague: 42 per cent of the Turkish and 23 per cent of the Moroccan children had plasma levels less than 20 nmol/l. In these groups hyperparathyroidism (PTH greater than 85 pmol/l) was significantly more prevalent. With all pooled data a significant correlation between plasma 25-OHD and PTH was observed (r = -0.24; P less than 0.001). Regression analysis indicated that the relationship between both variables did not differ among the three ethnic groups. As expected, 25-OHD concentrations were higher for increased CGSR. Differences in 25-OHD level are mainly explained by differences in skin pigmentation and calcium intake between Mediterranean and Caucasian children. The secondary hyperparathyroidism observed in some children confirms that migrant children have a higher risk of developing nutritional rickets when living in areas with a moderate climate.

Vitamin D: can an upper limit be defined?

Vitamin D ingested in excess results in hypercalcemia, which is caused by excessive absorption of massive quantities of calcium by the intestine and enhanced bone resorption. The symptoms of this intoxication include feeding difficulties, polydypsia, polyuria, irritability, lassitude and poor weight gain. Because daily intakes of 400 IU (10 microg) of vitamin D2 or D3 are completely safe, and because as low as 100 IU (2.5 microg) daily may prevent rickets, it is difficult to justify recent studies that attempt to firmly establish an upper limit of daily vitamin D intake in the normal neonate. Thus, despite efforts to better understand the upper limits of daily vitamin D intake, a concentration of 100 IU (2.5 g) of vitamin D per 100 kcal ingested, as is currently recommended by the Committee on Nutrition of the American Academy of Pediatrics, seems entirely appropriate.