A systematic review of evidence-based clinical guidelines for vitamin D screening and supplementation over the last decade.

Background: Amid growing evidence from observational data and trials with various results on the association between vitamin D and multiple diseases, numerous clinical guidelines were generated [1, 2]. The aims of this systematic review were to compare guidelines regarding recommendations for vitamin D screening and supplementation in the general adult population such as healthy people without pre-existing conditions or co-morbidities, but also for specific populations and find consensus for clinical practice.

Methods: A systematic electronic search for clinical guidelines was conducted in the following databases: PubMed, Embase (Ovid), Cochrane Reviews and Google Scholar for the period from January 2013 to June 2024. Guidelines related to vitamin D screening and supplementation, targeted to the general adult population as well as to specific populations, released in Europe or North America in English, were included. Guidelines only aimed at children and adolescents, pregnant or breastfeeding women were excluded.

Results: We identified 5853 records. After screening 92 full text studies, 31 guidelines were included for the final analysis. Two third of the guidelines recommended screening for people at risk for vitamin D deficiency, no guideline recommended screening for the general population. Almost one third recommended against any screening or did not specify, when screening would be appropriate. Half of the included guidelines recommended supplementation for people at risk, with varying definitions of people at risk. One third of these guidelines were aimed at people with osteoporosis and recommended vitamin D supplementation with varying doses, mainly with a dosage between 400 to 1000IU/day, one third recommended supplementation especially for the older population with a similar dosage, with varying age ranges for the definition of older people. There was no recommendation for supplementation for the general adult population without risk factors.

Conclusions: Clinicians base their clinical practice on guidelines to improve and standardize the care for their patients. During our research we found many guidelines with very different recommendations for screening and for supplementation of vitamin D deficiency, so it was difficult to get a consensus. However, no guideline recommended screening or supplementation for the general adult population. No clear consensus could be reached for older people, people with osteoporosis or people with conditions increasing the risk for vitamin D deficiency, but most guidelines targeting these populations recommended supplementation with 400 to 1000IU/d and a vitamin D threshold with a minimum of 50 to 75 nmol/l. In that matter, further research is needed to get more conclusive data to get a better understanding of the effects of vitamin D deficiency and the benefit of a sufficient vitamin D level to generate standardized evidence-based recommendations in clinical guidelines, especially for the general population.

Strengths and limitations of this research: The main strength of this systematic review is the robust search algorithm developed by experienced librarians. In addition, we applied clear and well-defined inclusion and exclusion criteria, focusing on the general adult population but also including specific populations, which enhanced the relevance of our findings to primary care practice. We used validated appraisal tools: the use of AGREE II ensured a structured and objective approach to assess guideline quality. The inclusion of guidelines up to mid-2024 makes the review current and highly relevant for clinical practice today. The findings may have potential implications for harmonizing international vitamin D recommendations and informing public health policy. Regarding the limitations, our analysis revealed that some guidelines neither contained clear recommendations, nor provided strong evidence, which made comparison between guidelines challenging. We excluded guidelines focusing on specific ethnicities outside of Europe or North America. While this may be considered a limitation, it was done with the understanding that certain geographic populations may have differing baseline vitamin D levels. We included guidelines, which referred to a systematic review conducted for this purpose. However, we did not assess the quality of each systematic review. Furthermore, the concept of evidence-based guidelines is complex, and it must be acknowledged that although a systematic review has been performed the included guidelines themselves may not be necessarily unequivocally evidence-based.