Serum 25-hydroxyvitamin D threshold and risk of rickets in young children: a systematic review and individual participant data meta-analysis to inform the development of dietary requirements for vitamin D.

PURPOSE: The objective of this systematic review was to determine a minimum serum 25-hydroxyvitamin D (25OHD) threshold based on the risk of having rickets in young children. This work was commissioned by the WHO and FAO within the framework of the update of the vitamin D requirements for children 0-3 years old. METHODS: A systematic search of Embase was conducted to identify studies involving children below  4 years of age with serum 25OHD levels and radiologically confirmed rickets, without any restriction related to the geographical location or language. Study-level and individual participant data (IPD)-level random effects multi-level meta-analyses were conducted. The odds, sensitivity and specificity for rickets at different serum 25OHD thresholds were calculated for all children as well as for children with adequate calcium intakes only. RESULTS: A total of 120 studies with 5412 participants were included. At the study-level, children with rickets had a mean serum 25OHD of 23 nmol/L (95% CI 19-27). At the IPD level, children with rickets had a median and mean serum 25OHD of 23 and 29 nmol/L, respectively. More than half (55%) of the children with rickets had serum 25OHD below 25 nmol/L, 62% below 30 nmol/L, and 79% below 40 nmol/L. Analysis of odds, sensitivities and specificities for nutritional rickets at different serum 25OHD thresholds suggested a minimal risk threshold of around 28 nmol/L for children with adequate calcium intakes and 40 nmol/L for children with low calcium intakes. CONCLUSION: This systematic review and IPD meta-analysis suggests that from a public health perspective and to inform the development of dietary requirements for vitamin D, a minimum serum 25OHD threshold of around 28 nmol/L and above would represent a low risk of nutritional rickets for the majority of children with an adequate calcium intake.

The Effect of Vitamin D on Metabolic Bone Disease and Chronic Diseases.

The history of vitamin D begins more than 100 years ago, with the initial documentation of rickets in industrialized cities of England [...].

Vitamin D deficiency rickets in a toddler.

ABSTRACT: Nutritional rickets is the failure of normal bone formation in children, caused by vitamin D deficiency, low calcium intake, or a combination of both. In the United States, prolonged breastfeeding without vitamin D supplementation is a major risk factor. Increasing awareness of the rationale for and importance of vitamin D supplements for all breastfed infants and children should reduce the incidence of vitamin D deficiency rickets and prevent bone deformity.

Nutritional rickets in Turkish and refugee children aged 0-2: an increasing problem despite vitamin D prophylaxis.

BACKGROUND: Nutritional rickets (NR) is still a major problem and is exacerbated by an increasing influx of immigrants. In this study, Turkish and immigrant cases followed with the diagnosis of NR in our pediatric endocrinology clinic were retrospectively evaluated. METHODS: Detailed data of cases diagnosed with NR between 2013 and 2020 and followed for at least six months were reviewed. RESULTS: In the study period, 77 cases of NR were identified. Turkish children constituted 76.6% (n=59) while 18 (23.4%) were immigrant children. The mean age at diagnosis was 8.1±7.8 months, 32.5% (n=25) were female, and 67.5% (n=52) were male. The 25-hydroxyvitamin D3 was below normal in all patients, with a mean value of 4.3±2.6 ng/mL. Parathyroid hormone (PTH) was above normal in all and the mean value was 301.7±139.3 pg/ mL. While there were 3.9 cases of NR in 10,000 endocrine clinic patients in 2013, this rate increased more than four-fold to 15.7 patients in 2019. CONCLUSIONS: Despite the vitamin D prophylaxis program in Türkiye, NR is seen significantly more frequently in recent years, which may be associated with an increasing number of refugees. High PTH levels indicate the severity of NR cases admitted to our clinic. However, clinically significant NR is only the tip of the iceberg and the true burden of subclinical rickets is unknown. Increasing compliance with the vitamin D supplementation program in refugee and Turkish children is important for the prevention of nutritional rickets.

Assessment, treatment and prevention of vitamin D deficiency.

Vitamin D deficiency is prevalent among various groups in the UK, and can result from insufficient sunlight exposure and dietary intake. There is a population-wide recommendation of 10 micrograms (400 international units) of vitamin D per day, with a daily supplement advised. However, supplement use is often suboptimal, compounding the risk of deficiency. Long-term vitamin D deficiency can cause rickets in children and osteomalacia or osteoporosis in adults. Therefore, it is important that nurses recognise which groups are at increased risk of vitamin D deficiency and understand how to assess people's vitamin D status. Nurses also need to be able to support the prevention and treatment of low vitamin D levels, which typically involves supplementation and lifestyle changes.

Vitamin D Deficiency in Chronic Childhood Disorders: Importance of Screening and Prevention.

Vitamin D plays a vital role in regulating calcium and phosphate metabolism and maintaining bone health. A state of prolonged or profound vitamin D deficiency (VDD) can result in rickets in children and osteomalacia in children and adults. Recent studies have demonstrated the pleiotropic action of vitamin D and identified its effects on multiple biological processes in addition to bone health. VDD is more prevalent in chronic childhood conditions such as long-standing systemic illnesses affecting the renal, liver, gastrointestinal, skin, neurologic and musculoskeletal systems. VDD superimposed on the underlying disease process and treatments that can adversely affect bone turnover can all add to the disease burden in these groups of children. The current review outlines the causes and mechanisms underlying poor bone health in certain groups of children and young people with chronic diseases with an emphasis on the proactive screening and treatment of VDD.

Variaciones y diferentes percepciones en la suplementación con vitamina D en la edad pediátrica en España / Variations and different perceptions in vitamin D supplementation in paediatric age in Spain

Introducción: el raquitismo es un problema de salud a nivel global. La deficiencia de vitamina D se ha convertido en una pandemia, su interés ha aumentado por la implicación de la misma en múltiples acciones extraesqueléticas. Material y métodos: se realizó una encuesta a través de correo electrónico entre pediatras españoles para estudiar su actitud en relación con la suplementación profiláctica de vitamina D. Resultados: un 83% de los pediatras tienen políticas de profilaxis de vitamina D en su área. Un 61,6% inicia la profilaxis en las dos primeras semanas y un 81,5% la mantiene el primer año. Un 57,2% realiza una búsqueda de deficiencia de vitamina D, sobre todo si trabajan en medio hospitalario. Conclusiones: las políticas de profilaxis con vitamina D son bastantes uniformes. Más de la mitad de los pediatras españoles realizan una búsqueda sistemática mediante analítica de deficiencia de vitamina D en sus pacientes con factores de riesgo durante la infancia y adolescencia (AU)

Introduction: rickets is a global health problem. Vitamin D deficiency has become a pandemic, its interest has increased due to its implication in multiple extraskeletal actions.Material and methods: a survey was conducted by e-mail among spanish paediatricians to study their attitude regarding prophylactic vitamin D supplementation.Results: 83% of pediatricians have vitamin D prophylaxis policies in their area. 61.6% start prophylaxis in the first two weeks, 81.5% maintain it the first year. 57.2% search for vitamin D deficiency, especially if they work in a hospital.Conclusions: vitamin D prophylaxis policies are uniform. More than a half of Spanish pediatricians conduct a systematic search for vitamin D deficiency in their patients with risk factors during childhood and adolescence (AU)

Infant and Maternal Vitamin D Supplementation: Clinician Perspectives and Practices.

INTRODUCTION: Rates of infant vitamin D supplementation fall short of guideline recommendations. We explored this discrepancy from the clinician perspective as they advise and affect this important intervention to prevent rickets. We compared infant and high-dose maternal vitamin D supplementation prescribing attitudes and practices between infant-only clinicians (IC) and clinicians who care for mothers and infants (MIC). METHODS: We surveyed clinicians in departments of family medicine, obstetrics/gynecology, primary care pediatrics, neonatology, newborn nursery, and members of vitamin D and rickets working groups and a social media group for lactation medicine providers about their perspectives and practices regarding vitamin D supplementation. RESULTS: 360 clinician survey responses were analyzed. In current practice, IC were more likely than MIC to recommend vitamin D supplementation to exclusively (P < .001) and partially breastfed infants (P = .005). MIC were more likely than IC to discuss infant and high-dose maternal supplementation options and let the parents/caregivers choose (34.7%, 22.0%, P = .009). If supplementing the mother with high-dose vitamin D or the infant directly each provided adequate vitamin D in the infant, MIC were more likely than IC to think that supplementation of the mother would be preferred by parents/caregivers (63.0%, 45.2%, P = .003), improve adherence (66.5%, 49.4%, P = .006), and promote breastfeeding (54.7%, 36.5%, P = .001); they were also more likely to recommend supplementation of the mother (17.7%, 8.9%, P = .04). CONCLUSIONS: MIC are more likely than IC to embrace high-dose maternal vitamin D supplementation to provide adequate vitamin D for infants. This highlights an opportunity for further education of clinicians about this option.

Impact of a Prenatal Vitamin D Supplementation Program on Vitamin D Deficiency, Rickets and Early Childhood Caries in an Alaska Native Population.

Background: Early childhood rickets increased in Alaska Native children after decreases in vitamin D-rich subsistence diet in childbearing-aged women. We evaluated the impact of routine prenatal vitamin D supplementation initiated in Alaska's Yukon Kuskokwim Delta in Fall 2016. Methods: We queried electronic health records of prenatal women with 25(OH) vitamin D testing during the period 2015−2019. We evaluated 25(OH)D concentrations, vitamin D3 supplement refills, and decayed, missing, and filled teeth (dmft) scores and rickets in offspring. Results: Mean 25(OH)D concentrations increased 36.5% from pre- to post-supplementation; the percentage with deficient 25(OH)D decreased by 66.4%. Women with ≥ 60 vitamin D3 refill days had higher late pregnancy 25(OH)D concentrations than those with no refill days (p < 0.0001). Women with late pregnancy insufficient 25(OH)D concentrations had offspring with higher dmft scores than those with sufficient 25(OH)D (RR 1.3, p < 0.0001). Three children were diagnosed with nutritional rickets during the period 2001−2021, and none after 2017. Conclusions: These findings suggest that prenatal vitamin D supplementation can improve childhood outcomes in high-risk populations with high rates of rickets.

800 IU versus 400 IU per day of vitamin D3 in term breastfed infants: a randomized controlled trial from an LMIC.

This open-label, block-randomized controlled trial compared the effect of 800 IU/day and 400 IU/day of oral vitamin D3 supplementation in reducing vitamin D insufficiency (VDI) among healthy-term breastfed infants at 14 weeks of postnatal age. All eligible infants were randomized to receive either 800 or 400 IU/day of oral vitamin D3 (starting within the first week until 14 weeks). The primary outcome was the proportion of infants with VDI (25-OH-D < 20 ng/ml) at 14 weeks. Secondary outcomes were vitamin D deficiency (VDD, < 12 ng/ml), severe VDD (< 5 ng/ml), anthropometry, biochemical or clinical rickets, and any adverse events related to vitamin D toxicity (VDT). Among 102 enrolled infants, the distribution of baseline variables (including cord 25-OH-D levels; 13.0 versus 14.2 ng/ml) was similar in both groups. On intention-to-treat analysis, the proportions of infants with VDI at 14 weeks were significantly lower in the 800 IU group compared to those in the 400 IU group [24% versus 55%; RR 0.44; 95% CI: 0.25-0.76]. The proportions of infants with elevated parathormone (6% versus 26.5%; p = 0.012) and severe VDD (0% versus 12.2%; p = 0.033) were significantly lower in the 800 IU group. Clinical rickets developed in three (6.2%) infants in the 400 IU group. No infant developed VDT.      Conclusions: Daily oral supplementation with 800 IU of vitamin D3 resulted in an almost 50% reduction in the proportion of infants with VDI and prevented the occurrence of severe VDD at 14 weeks of age compared to 400 IU with no evidence of vitamin D toxicity.     Trial Registration: Clinical Trial Registry of India (CTRI/2019/02/017374). What is Known: • Breastfeeding is the ideal source of nutrition for healthy-term breastfed infants; however, vitamin D content of breastmilk is suboptimal. • AAP recommends daily oral supplementation of 400 IU of vitamin D to all healthy-term breastfed infants; however, trials from high-income countries support insufficiency of this dose in maintaining serum 25-OH-D levels >20 ng/ml with no such information from low-middle-income countries. What is New: • 800 IU/day of oral vitamin D3 supplementation among term breastfed infants significantly reduces vitamin D insufficiency at 14 weeks' age as compared to the recommended dose of 400 IU/day. • This higher supplemental dose is safe with no evidence of vitamin D toxicity.

25(OH)Vitamin D Deficiency and Calcifediol Treatment in Pediatrics.

Vitamin D is essential for the normal mineralization of bones during childhood. Although diet and adequate sun exposure should provide enough of this nutrient, there is a high prevalence of vitamin D deficiency rickets worldwide. Children with certain conditions that lead to decreased vitamin D production and/or absorption are at the greatest risk of nutritional rickets. In addition, several rare genetic alterations are also associated with severe forms of vitamin-D-resistant or -dependent rickets. Although vitamin D3 is the threshold nutrient for the vitamin D endocrine system (VDES), direct measurement of circulating vitamin D3 itself is not a good marker of the nutritional status of the system. Calcifediol (or 25(OH)D) serum levels are used to assess VDES status. While there is no clear consensus among the different scientific associations on calcifediol status, many clinical trials have demonstrated the benefit of ensuring normal 25(OH)D serum levels and calcium intake for the prevention or treatment of nutritional rickets in childhood. Therefore, during the first year of life, infants should receive vitamin D treatment with at least 400 IU/day. In addition, a diet should ensure a normal calcium intake. Healthy lifestyle habits to prevent vitamin D deficiency should be encouraged during childhood. In children who develop clinical signs of rickets, adequate treatment with vitamin D and calcium should be guaranteed. Children with additional risk factors for 25(OH)D deficiency and nutritional rickets should be assessed periodically and treated promptly to prevent further bone damage.

Indian Academy of Pediatrics Revised (2021) Guidelines on Prevention and Treatment of Vitamin D Deficiency and Rickets.

JUSTIFICATION: The emerging literature on prevalence of vitamin D deficiency in India, prevention and treatment strategies of rickets, and extra-skeletal benefits of vitamin D suggest the need for revising the existing guidelines for prevention and treatment of vitamin D deficiency in India. OBJECTIVES: To review the emerging literature on vitamin D prevalence and need for universal vitamin D supplementation. To suggest optimum vitamin D therapy for treatment of asymptomatic and symptomatic vitamin D deficiency, and rickets. To evaluate the extra-skeletal health benefits of vitamin D in children. PROCESS: A National consultative committee was formed that comprised of clinicians, epidemiologists, endocrinologists, and nutritionists. The Committee conducted deliberations on different aspects of vitamin D deficiency and rickets through ten online meetings between March and September, 2021. A draft guideline was formulated, which was reviewed and approved by all Committee members. RECOMMENDATIONS: The group reiterates the serum 25-hydroxy vitamin D cutoffs proposed for vitamin D deficiency, insufficiency, and sufficiency as <12 ng/mL, 12-20 ng/mL and >20 ng/mL, respectively. Vitamin D toxicity is defined as serum 25OHD >100 ng/mL with hypercalcemia and/or hypercalciuria. Vitamin D supplementation in doses of 400 IU/day is recommended during infancy; however, the estimated average requirement in older children and adolescents (400-600 IU/day, respectively) should be met from diet and natural sources like sunlight. Rickets and vitamin D deficiency should be treated with oral cholecalciferol, preferably in a daily dosing schedule (2000 IU below 1 year of age and 3000 IU in older children) for 12 weeks. If compliance to daily dosing cannot be ensured, intermittent regimens may be prescribed for children above 6 months of age. Universal vitamin D supplementation is not recommended in childhood pneumonia, diarrhea, tuberculosis, HIV and non-infectious conditions like asthma, atopic dermatitis, and developmental disorders. Serum 25-hydroxy vitamin D level of >20 ng/mL should be maintained in children with conditions at high-risk for vitamin deficiency, like nephrotic syndrome, chronic liver disease, chronic renal failure, and intake of anticonvulsants or glucocorticoids.

A major health problem facing immigrant children: nutritional rickets.

OBJECTIVES: Nutritional rickets (NR) is still an important problem and one which increasing influxes of immigrants are further exacerbating. This study evaluated cases of mostly immigrant children followed up with diagnoses of NR in our pediatric endocrinology clinic. METHODS: Details of 20 cases diagnosed with NR between 2017 and 2020 were retrieved from file records. RESULTS: Twenty (11 male) cases were included in the study. Three (15%) were Turkish nationals and the others (85%) were immigrants. Hypocalcemia and hypophosphatemia were detected in 17 and 13, respectively. Alkaline phosphatase (ALP) values were normal in two cases, while ALP and parathyroid hormone (PTH) values were elevated in all other cases, and PTH levels were very high (473.64 ± 197.05 pg/mL). 25-hydroxyvitamin D levels were below 20 ng/mL in all cases. Patients with NR received high-dose long-term vitamin D or stoss therapy. Six patients failed to attend long-term follow-up, while PTH and ALP levels and clinical findings improved at long-term follow-up in the other 14 cases. CONCLUSIONS: The elevated PTH levels suggest only the most severe cases of NR presented to our clinic. Clinically evident NR is therefore only the tip of the iceberg, and the true burden of subclinical rickets and osteomalacia remains unidentified. Public health policies should therefore focus on universal vitamin D supplementation and adequate dietary calcium provision, their integration into child surveillance programs, adequate advice and support to ensure normal nutrition, exposure to sunlight, and informing families of the increased risk not only for resident populations but also for refugee and immigrant children.

[Kurt Huldschinsky: A pioneer in the struggle against rickets]. / Kurt Huldschinsky: Ein Vorreiter im Kampf gegen Rachitis.

Kurt Huldschinsky (1883-1940) was a German pediatrician who was one of the international leaders in the field of rickets research between the two world wars. After his medical studies, he served at the Kaiserin-Auguste-Victoria-Haus in Berlin and at the University Children's Hospital in Vienna, among other places. After World War I, he worked with the famous orthopedist Konrad Biesalski at the Oskar-Helene-Heim for the healing and education of frail children in Berlin. Here he was the first to prove that exposure to ultraviolet (UV) radiation from mercury vapor lamps ("artificial sunlight") could cure rickets in young children, which is mostly caused by vitamin D deficiency. He published his discovery in this journal - the Deutsche Medizinische Wochenschrift [German Medical Weekly] - in 1919. For this groundbreaking scientific achievement and his further research into the prevention and treatment of rickets, Huldschinsky was awarded the Otto Heubner Prize of the German Association of Pediatrics in 1926. He was even nominated for the Nobel Prize in Medicine. As a Jew, however, he had to flee Germany from the National Socialists in 1933/34. Together with his wife and daughter, he emigrated to Egypt, where he died in Alexandria on October 31, 1940. As Huldschinsky was for many decades almost forgotten, this article recalls the life and work of a meritorious physician and scientist.

Vitamin D deficiency, supplementation and testing: have we got it right in New Zealand?

BACKGROUND: Severe prolonged vitamin D deficiency can cause rickets or osteomalacia. Both can be prevented by sunshine exposure or vitamin D supplementation. Although New Zealand guidance does not recommend vitamin D supplementation for the general population, it can be considered for individuals at risk of vitamin D deficiency. Routine measurement of 25-hydroxyvitamin D (25OHD) is also considered unnecessary. METHODS: We investigated the rates of vitamin D supplementation, rickets and osteomalacia in New Zealand, and of 25OHD results in Auckland, over the last two decades. RESULTS: Vitamin D prescriptions increased 14-fold, from 86,295/year to 1,215,507/year, between 2003 and 2019, with medication costs alone in 2019 being >$1 million. Despite these changes, the annual prevalence of hospital admissions for rickets, osteomalacia and unspecified vitamin D deficiency remained low and stable (10-20/year). 25OHD concentrations increased between 2002 and 2003 and between 2009 and 2019, and in the later time-period, 25OHD tests mainly identified individuals without vitamin D deficiency (40-50% >75nmol/L, 65-70% >50nmol/L and only 7-12.5% <25nmol/L). CONCLUSIONS: Osteomalacia and rickets persist at low rates despite widespread, increasingly costly vitamin D supplementation and testing, which largely identifies individuals without vitamin D deficiency. These results suggest that vitamin D guidance and practice in New Zealand should change.

Vitamin D prophylaxis in infancy.

We looked at existing recommendations and supporting evidence on the effectiveness of vitamin D supplementation in infancy for reducing vitamin D deficiency and for preventing rickets and infections. We also looked at optimal dose of vitamin D and the age until which vitamin D supplementation is beneficial.We conducted a literature search up to the 17th of July 2019 by using key terms and manual search in selected sources. We summarized the recommendations and the strength of the recommendation when and as reported by the authors. We summarized the main findings of systematic reviews with the certainty of the evidence as reported.A daily dose of 400 international units of vitamin D in infants has shown to be effective for improving bone health and preventing rickets. Evidence is more robust in groups of infants and children at risk. Vitamin D supplementation is well tolerated, and not associated with toxicity. Higher doses have not shown to add benefit while it could potentially cause toxic blood levels and hypercalcemia. Adequate levels of vitamin D might not be achieved with lower daily doses. Universal vitamin D supplementation starting shortly after birth, regardless of the mode of feeding and until 12 months of age, is strongly recommended. Beyond 12 months of age vitamin D supplementation is recommended only in groups of children at risk.

Serum 25-hydroxyvitamin D requirements to prevent nutritional rickets in Nigerian children on a low-calcium diet-a multivariable reanalysis.

BACKGROUND: Nutritional rickets is believed to result from the interaction of inadequate serum 25-hydroxyvitamin D [25(OH)D] concentration and dietary calcium intake, but this interaction has not been confirmed in children with rickets. Determining the vitamin D requirements to prevent nutritional rickets has been thwarted by inconsistent case definition, inadequate adjustment for calcium intake and other confounders, and 25(OH)D assay variability. OBJECTIVES: To model the 25(OH)D concentration associated with nutritional rickets in calcium-deprived Nigerian children, adjusted for confounding factors, and develop a general approach to define vitamin D status while accounting for calcium intake. METHODS: Logistic regression was used to model the association of serum 25(OH)D with having rickets adjusted for calcium intake in a reanalysis of a case-control study in Nigerian children. The matching variables age, sex, weight-for-age z score, and 4 additional significant variables were selected [religion, age began walking, phosphorus intake, and the 25(OH)D × calcium intake interaction] using a rigorous 7-step algorithm. RESULTS: Cases had significantly (P < 0.0001) lower mean ± SD 25(OH)D than controls (33 ± 13 compared with 51 ± 16 nmol/L, respectively), whereas cases and controls had similarly (P = 0.81) low mean dietary calcium intakes (216 ± 88 and 213 ± 95 mg/d, respectively). There was a significant interaction between 25(OH)D and calcium intake [coefficient (95% CI): -0.0006 (-0.0009, -0.0002)]. Accordingly, as calcium intake increased from 130 to 300 mg/d, the adjusted odds of having rickets decreased dramatically with increasing 25(OH)D such that at 200 mg/d, the adjusted odds of having rickets at 47.5 nmol/L was 0.80, whereas it was 0.2 at 62.5 nmol/L. Moreover, at a calcium intake of 300 mg/d, the adjusted odds was 0.16 at a 25(OH)D concentration of 47.5 nmol/L and 0.02 at 62.5 nmol/L. CONCLUSIONS: The vitamin D requirement to prevent nutritional rickets varies inversely with calcium intake and vice versa. Also, application of multivariable modeling is essential in defining vitamin D requirements.

Perspective: Vitamin D supplementation prevents rickets and acute respiratory infections when given as daily maintenance but not as intermittent bolus: implications for COVID-19.

The value of vitamin D supplementation in the treatment or prevention of various conditions is often viewed with scepticism as a result of contradictory results of randomised trials. It is now becoming apparent that there is a pattern to these inconsistencies. A recent large trial has shown that high-dose intermittent bolus vitamin D therapy is ineffective at preventing rickets - the condition that is most unequivocally caused by vitamin D deficiency. There is a plausible biological explanation since high-dose bolus replacement induces long-term expression of the catabolic enzyme 24-hydroxylase and fibroblast growth factor 23, both of which have vitamin D inactivating effects. Meta-analyses of vitamin D supplementation in prevention of acute respiratory infection and trials in tuberculosis and other conditions also support efficacy of low dose daily maintenance rather than intermittent bolus dosing. This is particularly relevant during the current COVID-19 pandemic given the well-documented associations between COVID-19 risk and vitamin D deficiency. We would urge that clinicians take note of these findings and give strong support to widespread use of daily vitamin D supplementation.

Vitamin D for Growth and Rickets in Stunted Children: A Randomized Trial.

BACKGROUND AND OBJECTIVES: Vitamin D is essential for healthy development of bones, but little is known about the effects of supplementation in young stunted children. Our objective was to assess the effect of vitamin D supplementation on risk of rickets and linear growth among Afghan children. METHODS: In this double-blind, placebo-controlled trial, 3046 children ages 1 to 11 months from inner-city Kabul were randomly assigned to receive oral vitamin D3 (100 000 IU) or placebo every 3 months for 18 months. Rickets Severity Score was calculated by using wrist and knee radiographs for 631 randomly selected infants at 18 months, and rickets was defined as a score >1.5. Weight and length were measured at baseline and 18 months by using standard techniques, and z scores were calculated. RESULTS: Mean (95% confidence interval [CI]) serum 25-hydroxyvitamin D (seasonally corrected) and dietary calcium intake were insufficient at 37 (35-39) nmol/L and 372 (327-418) mg/day, respectively. Prevalence of rickets was 5.5% (placebo) and 5.3% (vitamin D): odds ratio 0.96 (95% CI: 0.48 to 1.92); P = .9. The mean difference in height-for-age z score was 0.05 (95% CI: -0.05 to 0.15), P = .3, although the effect of vitamin D was greater for those consuming >300 mg/day of dietary calcium (0.14 [95% CI: 0 to 0.29]; P = .05). There were no between-group differences in weight-for-age or weight-for-height z scores. CONCLUSIONS: Except in those with higher calcium intake, vitamin D supplementation had no effect on rickets or growth.