SOS Hypovitaminosis D: 60% of children with deficiency? What we know today

In brief

• Vitamin D is crucial for bone health at all ages; deficiency is common in many populations, including children and adolescents.
• Risk factors include poor sun exposure, darker skin, exclusive breastfeeding without prophylaxis, adolescence, and obesity.
• Evidence shows associations between low 25(OH)D levels and various conditions; however, clinical benefit evidence for many extra-skeletal diseases is limited or conflicting.
• In infants and children, rickets prevention remains a priority; recommendations suggest targeted supplementation in at-risk groups.
• For individual decisions on testing and supplementation, it is advisable to consult a healthcare professional who considers risk factors and context.

Abstract: what does science say?

Vitamin D is a micronutrient primarily produced by skin synthesis after sun exposure and, to a lesser extent, taken in with certain foods or supplements. Epidemiological evidence shows a high prevalence of hypovitaminosis in many areas, including pediatric groups; the most robust associated factors are reduced sun exposure, skin pigmentation, exclusive breastfeeding without prophylaxis, adolescence, and excess weight. Skeletally, deficiency can cause rickets in children and impair bone mass acquisition; for this reason, there are targeted recommendations for supplementation in pediatric age. For extra-skeletal outcomes (respiratory infections, cardiovascular diseases, cancers, diabetes, mood disorders), the literature reports observational associations, but evidence of supplement efficacy in clinical trials is largely conflicting or negative for preventive effects in the general population. Targeted interventions for individuals with actual deficiency seem more consistent with biological plausibility. Methodological limitations (heterogeneity of definitions, doses, duration, populations) require interpretive caution.

Hypovitaminosis: between risks and pathologies

In Italy and many European countries, vitamin D deficiency among children and adolescents is recognized as a frequent problem: national recommendations and pediatric consensuses report a high prevalence of hypovitaminosis in the infant and youth population, with percentages varying according to the thresholds used and the areas studied. [1] More recent studies on Italian school cohorts also confirm that many children have 25-hydroxyvitamin D levels below the thresholds defined as optimal by some expert groups. [2]

Established risk factors include reduced exposure to sunlight (seasonality and indoor behaviors), increased skin pigmentation, exclusive breastfeeding without vitamin D prophylaxis, clinical conditions that alter absorption or metabolism (e.g., liver or kidney diseases), and chronic use of certain medications. Obesity is consistently associated with lower 25(OH)D levels; observational meta-analyses show an increased prevalence of deficiency in people with excess weight, including in pediatric age. [3]

Clinically, the strongest relationship is with skeletal health: severe deficiency causes rickets in children and can impair bone mass accumulation in adolescence, with possible long-term consequences. For the prevention and management of rickets and conditions related to vitamin D deficiency, there are international recommendations that define thresholds, at-risk groups, and prevention strategies. [4] The concise guidelines of endocrine societies, on the other hand, specify diagnostic criteria, 25(OH)D ranges, and recommendations for diagnosis and treatment. [5]

What this means in practice

The available evidence defines an operational framework: vitamin D is essential for bone growth and rickets prevention; for other possible benefits (cardiovascular, oncological, metabolic, or psychological), large-scale randomized trials have not yet provided clear confirmation of a protective effect when supplementation is administered to unselected populations. Therefore, effective and recommended practical actions are based on identifying at-risk groups and targeted prevention measures. [6]

Children and infants

For infants and the first year of life, established recommendations indicate prophylaxis with a standard dose (e.g., 400 IU/day) to prevent rickets regardless of the type of feeding; in the presence of risk factors or in premature infants, higher doses or monitoring are provided. These recommendations derive from international pediatric consensuses and aim to reduce preventable cases of rickets and ensure adequate skeletal development. [4]

Adolescents, adults, and people with obesity

During adolescence, a significant portion of bone mass accumulation occurs; for this reason, professionals evaluate risk factors and, if necessary, propose personalized supplementation. In people with obesity, the level of 25(OH)D tends to be lower and may require higher doses to reach circulating concentrations comparable to those of normal-weight individuals; however, supplementation studies do not convincingly demonstrate that supplementation leads to significant improvements in metabolic control or weight loss when not targeted at deficient individuals. [3]

Sun exposure, diet, and supplementation

Most vitamin D is produced cutaneously after sun exposure; dietary intake from foods is limited (fatty fish, cod liver oil, eggs, fortified foods). Considering geographical, seasonal, and behavioral variability, the most effective strategy to prevent deficiency is to combine public policies (information, targeted fortification if necessary), individual measures (risk assessment), and, when indicated, supplementation. [5]

Key takeaways

• Vitamin D is fundamental for bone health; rickets prevention in infants is a recognized priority.
• Many environmental and biological factors (sunlight, pigmentation, obesity, medications) influence 25(OH)D levels.
• Observational associations between low vitamin D levels and numerous diseases do not automatically imply that supplementation prevents these conditions.
• Clinical recommendations favor targeted supplementation for at-risk groups rather than generalized use for chronic disease prevention in the general population.
• For individual choices regarding testing and supplementation, it is advisable to consult a healthcare professional who evaluates the risk and clinical context.

Limitations of the evidence

It is important to distinguish between observational evidence and causal evidence provided by randomized trials. Observational studies have identified many associations between low 25(OH)D and clinical conditions (infections, cardiovascular diseases, cancers, metabolic disorders), but these analyses are susceptible to residual confounding (e.g., outdoor activity, nutritional status, comorbidities) and do not establish causality. Recent major randomized trials, conducted on unselected populations, have not shown consistent benefits of supplementation in terms of reducing cardiovascular events or cancer incidence in the general population. [7][8]

For specific outcomes, such as the prevention of respiratory infections, individual-participant data meta-analyses indicate modest reductions in risk, but the effect is more evident in those who were severely deficient and when supplementation is given regularly (not in large intermittent doses). [6] For the prevention of diabetes in high-risk individuals, a large multicenter trial did not show significant reductions in progression to diabetes with high doses compared to placebo. [9]

Other recurring methodological limitations: variability in 25(OH)D measurements, non-uniform thresholds for defining deficiency/insufficiency, heterogeneity of dose and duration of interventions, and poor representativeness of ethnic groups or specific clinical conditions. All of this requires caution in interpretation and a clinical choice based on the individual patient and official recommendations.

Editorial conclusion

Vitamin D remains an essential element for skeletal health and development in children; rickets prevention and the maintenance of adequate circulating levels in at-risk groups are shared goals of the medical community. For other presumed extra-skeletal benefits, the available evidence does not justify the generalized use of supplementation in the non-deficient adult population. Clear communication to parents, identification of at-risk individuals, and the application of guideline-based recommendations remain the most institutional and prudent way to address the problem of vitamin D hypovitaminosis.

Editorial note

The article has been updated with reference to pediatric consensuses and international systematic reviews. The information reported here is for divulgative purposes and does not replace a visit or specialist consultation. For personalized therapeutic or diagnostic indications, consult your primary care physician or specialist.

Scientific research

1. Saggese G, Vierucci F, Prodam F, et al. Vitamin D in pediatric age: consensus of the Italian Pediatric Society and the Italian Society of Preventive and Social Pediatrics, jointly with the Italian Federation of Pediatricians. Ital J Pediatr. 2018;44:51. https://doi.org/10.1186/s13052-018-0488-7
2. Vitamin D status in healthy Italian school-age children: a single-center cross-sectional study. Ital J Pediatr. 2023;49:27. https://doi.org/10.1186/s13052-023-01422-x
3. Pereira‑Santos M, Costa PRF, Assis AMO, Santos CAST, Santos DB. Obesity and vitamin D deficiency: a systematic review and meta‑analysis. Obes Rev. 2015;16(4):341–349. https://doi.org/10.1111/obr.12239
4. Munns CF, Shaw N, Kiely M, et al. Global consensus recommendations on prevention and management of nutritional rickets. J Clin Endocrinol Metab. 2016;101(2):394–415. https://doi.org/10.1210/jc.2015-2175
5. Holick MF, Binkley NC, Bischoff‑Ferrari HA, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(7):1911–1930. https://doi.1210/jc.2011-0385
6. Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta‑analysis of individual participant data. BMJ. 2017;356:i6583. https://doi.org/10.1136/bmj.i6583
7. Manson JE, Cook NR, Lee IM, et al; VITAL Research Group. Vitamin D supplements and prevention of cancer and cardiovascular disease. N Engl J Med. 2019;380:33–44. https://doi.org/10.1056/NEJMoa1809944
8. Barbarawi M, Kheiri B, Zayed Y, et al. Vitamin D Supplementation and Cardiovascular Disease Risks in More Than 83,000 Individuals in 21 Randomized Clinical Trials: A Meta‑analysis. JAMA Cardiol. 2019;4(8):765–776. https://doi.org/10.1001/jamacardio.2019.1870
9. Pittas AG, Dawson‑Hughes B, Sheehan P, et al; D2d Research Group. Vitamin D supplementation and prevention of type 2 diabetes. N Engl J Med. 2019;381(6):520–530. https://doi.org/10.1056/NEJMoa1900906