Discussion

This study evaluated paediatricians’ reported practices and opinions regarding vitamin D management in children and adolescents aged 3–17 years in Geneva, Switzerland. The findings revealed notable variability, particularly in the assessment of VDA, with inconsistent practices reported even for children with clinical signs of deficiency. At the same time, most paediatricians supported systematic supplementation, while those opposed frequently cited the absence of clear Swiss guidelines, highlighting the urgent need for harmonized recommendations to support consistent practice.

Less than half of paediatricians reported assessing VDA at every check-up for children without specific risk factors, with adolescents receiving less consistent attention. For children with risk factors, this proportion ranged from 46% to 65%, depending on the condition. Only 76% of paediatricians reported assessing VDA at every check-up in children presenting with clinical signs of deficiency, a proportion lower than expected. These practices also reflected paediatricians’ perceptions of deficiency risk: one-third estimated that 25% of their patients were at risk, another third estimated 50%, and the remainder estimated 75%.

The prevalence of suboptimal vitamin D levels in Swiss children and adolescents is high (35–50%)^{(Reference Ramelli, Ramelli, Lava, Siegenthaler, Cantù and Bianchetti9–Reference Parel, Bochud, Rezzi, Chatelan and Jotterand Chaparro11)} and aligns with European data.^{(Reference Braegger, Campoy, Colomb, Decsi, Domellof and Fewtrell3)} The prevalence is even higher in subgroups of children with established risk factors for vitamin D deficiency and fractures, including overweight and obesity,^{(Reference Fiamenghi and Mello33,Reference Varkal, Gulenc, Yildiz, Kandemir, Bilgili and Toprak34)} which affects around 15% of Swiss children and adolescents.^{(Reference Narvaez, Mahler, Baratti-Mayer and Jeannot24,25)} In a Swiss study, nearly 90% of adolescents attending a reference centre for obesity had low vitamin D levels.^{(Reference Patriota, Borloz, Ruiz, Bouthors, Rezzi and Marques-Vidal35)} Despite this, only 58% of paediatricians in our survey reported assessing VDA at every check-up for overweight or obese children. Similarly, a recent French survey found that only 40% of paediatricians recognized obesity as a risk factor.^{(Reference Pechabrier, Bacchetta, Tounian, Eddiry, Linglart and Edouard30)}

We observed similar underassessment for children with dark skin, whereas studies have shown elevated deficiency rates in migrant children from African and also Eastern Mediterranean regions.^{(Reference Fahrni, Wilhelm-Bals, Posfay-Barbe and Wagner23,Reference Karagol and Duyan Camurdan36–Reference Lane, Nisbet, Whiting and Vatanparast38)} Assessment was also inconsistent in other medical risk groups, including children receiving long-term corticosteroids and those with gastrointestinal disorders or disabilities, with only 46–64% of paediatricians reporting assessment at every check-up. These results may reflect uncertainties about which factors warrant evaluation, competing priorities, time constraints, or insufficiently standardized assessment methods. Although this study was conducted in a single canton, Geneva has a diverse paediatric population with recognized risk factors for vitamin D deficiency, including overweight/obesity and children from migrant backgrounds, which may reflect challenges encountered in other urban European contexts.

Regarding VDA assessment methods, paediatricians mainly evaluated supplementation (68%), dietary intake (56%), and sun exposure (48%). Only 37% used blood tests, consistent with guidelines that do not recommend routine testing.^{(Reference Saggese, Vierucci, Prodam, Cardinale, Cetin and Chiappini16,Reference Bacchetta, Edouard, Laverny, Bernardor, Bertholet-Thomas and Castanet18)} A previous Swiss survey (2016–2017) reported that 88% of paediatricians ordered these tests when deficiency was suspected.^{(Reference Santi, Janner, Simonetti and Lava28)} Our findings may reflect recent changes in Swiss reimbursement policies, which now restrict coverage for these tests to reduce costs .^{(Reference Folino, Durieux-Paillard, Biver, Ferrari and Richtering39)} Indications for measuring serum vitamin D beyond symptoms of rickets vary widely across organizations and scientific societies, as do the serum 25-hydroxyvitamin D thresholds used to define vitamin D insufficiency and deficiency, which may contribute to variability in clinical practice.^{(Reference Saggese, Vierucci, Prodam, Cardinale, Cetin and Chiappini16)}

Assessing dietary intake is also challenging, as vitamin D-rich foods such as fatty fish or fortified products are rarely consumed by most European children, resulting in low intake.^{(Reference Spiro and Buttriss2)} In Switzerland, median vitamin D intake among adolescents is only 0.9 µg/day,^{(Reference Parel, Bochud, Rezzi, Chatelan and Jotterand Chaparro11)} far below the recommended 15 µg/day.⁽⁶⁾ Only 20% of paediatricians mentioned fatty fish when discussing dietary interventions. Although dairy products are more commonly consumed, they are rarely fortified with vitamin D in Switzerland. Calcium is essential for bone health, but its absorption depends on adequate vitamin D, reinforcing the importance of sufficient vitamin D intake.^{(Reference Fleet40)}

Sun exposure assessment also presents challenges, as seasonal UVB variation makes vitamin D synthesis unreliable for much of the year at Swiss latitude. Although brief sun exposure (around 10–15 minutes) may be sufficient in spring and summer, endogenous synthesis is negligible between approximately October and March.^{(Reference Religi, Backes, Chatelan, Bulliard, Vuilleumier and Moccozet4)} During this period, the duration required to achieve adequate vitamin D production would be considerably longer (up to 1.5–6.5 hours with face and hands exposed), making it largely impracticable and potentially associated with sunburn. Despite these constraints, two-thirds of paediatricians in our sample reported recommending sun exposure and dietary measures in addition to vitamin D supplementation. This suggests awareness of the multifactorial determinants of VDA, although these practical constraints further support the need for supplementation strategies.

For children with serum total 25-hydroxyvitamin D concentrations <50 nmol/L, nearly all paediatricians recommended supplementation, which is consistent with current scientific guidelines.^{(Reference Munns, Shaw, Kiely, Specker, Thacher and Ozono1)} This finding is in line with a European survey conducted in 33 countries, where paediatricians demonstrated good knowledge of hypovitaminosis D and appropriate supplementation strategies.^{(Reference Petrović, Runjić, Buljan, Jeličić Kadić and Markić27)}

Approaches to preventive supplementation in the general paediatric population vary substantially across countries.^{(Reference Randev, Kumar and in Childhood17)} In Switzerland, supplementation is recommended only for children under three years or those with identified hypovitaminosis D or risk factors,^{(5,Reference Quack Lötscher, l’Allemand, Bischoff-Ferrari and Burckhardt10)} whereas several European countries recommend broader year-round supplementation.⁽¹⁹⁾ In our survey, 65% of paediatricians supported systematic supplementation for children aged 3–10 years and 76% for those aged 11–17 years, contrasting with the 2016–2017 Swiss survey, in which paediatricians rarely prescribed vitamin D for these age groups.^{(Reference Santi, Janner, Simonetti and Lava28)} In countries with national recommendations for systematic supplementation, adherence is high,^{(Reference De Crem, Van Winckel, Vandenplas and Raaijmakers29,Reference Pechabrier, Bacchetta, Tounian, Eddiry, Linglart and Edouard30)} with more than 90% of French paediatricians following these recommendations. These findings suggest that the absence of national recommendations for systematic supplementation may contribute to the variability in clinical practice observed in this study, where two-thirds of paediatricians opposed to systematic supplementation cited the lack of clear national guidelines as their main reason. Similar challenges may arise in other European countries without such recommendations.

Dosage preferences for supplementation also varied. Among paediatricians treating children aged 3–10 years, 57% recommended 400–600 IU/day during fall and winter, whereas 30% preferred a loading dose of 80,000–100,000 IU, increasing to 50% for adolescents. This may reflect concerns about poor adherence. Only one third of paediatricians considered that the majority of children aged 3–10 years were adherent, in line with studies reporting that fewer than 30% of infants comply with national vitamin D recommendations.^{(Reference Thia, Lorrain, Richard, Lapillonne and Iacobelli41,Reference Hemmingway, Fisher, Berkery, Murray and Kiely42)} Among adolescents, nearly half of paediatricians estimated that only 10–25% adhered to supplementation, mainly due to forgetfulness, consistent with poor adherence reported in adolescent medicine.^{(Reference Nassetta, Hussain, Gambetta, Le, O’Dwyer and Badawy43)} Although French guidelines recommend daily supplementation as first-line, they also allow intermittent high-dose regimens in selected cases of poor adherence, often administered during autumn and winter.^{(Reference Bacchetta, Edouard, Laverny, Bernardor, Bertholet-Thomas and Castanet18)} Similarly, most European guidelines do not consider high-dose regimens standard prophylactic practice. Beyond dosing strategies, adherence improves when parents receive appropriate counselling from health professionals, highlighting the potential role of parental education.

Taken together, our findings highlight the need for targeted education for paediatricians, clearer Swiss national guidelines for children over three years, and standardized tools such as validated decision algorithms to guide the assessment of VDA. Guidelines should clarify how to identify at-risk children and assess dietary intake, supplementation, sun exposure, and adherence. Food fortification may also represent a complementary strategy.^{(Reference Cashman and O’Neill44)} Some countries have adopted mandatory fortification,^{(Reference Itkonen, Erkkola and Lamberg-Allardt45)} whereas Switzerland relies mainly on voluntary fortification.⁽⁵⁾ Meta-analyses show that children with low vitamin D levels benefit most from supplementation, with positive effects on bone health and overall well-being.^{(Reference Winzenberg, Powell, Shaw and Jones13,Reference Martineau, Jolliffe, Hooper, Greenberg, Aloia and Bergman14)} Standardizing practices could therefore reduce deficiency in childhood and contribute to preventing later-life complications, potentially lowering healthcare costs related to osteoporosis.⁽⁴⁶⁾

This study has certain limitations. Some questions required paediatricians to estimate patient behaviours, such as adherence to supplementation, which may not fully reflect actual practices. In addition, paediatricians were asked to estimate the prevalence of children at risk of vitamin D deficiency in their practice without a predefined serum threshold. Different serum thresholds may therefore have been applied, contributing to the heterogeneity observed. The response rate of 30% may have introduced selection bias, as paediatricians more interested in vitamin D might have been more likely to participate. The self-reported nature of the survey also carries a risk of social desirability bias. However, if VDA is not assessed at every check-up even among paediatricians more engaged with the topic, practices in the broader paediatric community may be even less consistent. This underscores the need for clearer guidelines, strengthened training, and larger-scale investigations.

Despite these limitations, the study has several strengths. To our knowledge, it is the first to comprehensively examine paediatricians’ approaches to VDA in Switzerland and in Europe among children aged 3–17 years, an age group often overlooked in national prevention strategies. By including both private and institutional paediatricians, the survey captures diverse practices. The questionnaire, developed using current literature and expert input, ensures good content validity. By integrating the concept of VDA, which encompasses risk factors, diet, sun exposure, and supplementation, the study offers a broad and nuanced picture of how paediatricians in Geneva manage vitamin D in practice.