This clinical practice guideline, based on a systematic review of randomized trials, suggests empiric vitamin D supplementation for children and adolescents (1-18 years) to prevent nutritional rickets and potentially reduce respiratory tract infections, adults over 75 years to reduce mortality risk, pregnant individuals to lower risks of complications such as pre-eclampsia, and those with high-risk prediabetes to reduce progression to diabetes. The guideline generally suggests *against* routine vitamin D supplementation beyond the recommended dietary allowance for other adult populations and *against* routine 25(OH)D screening for all populations considered, due to insufficient evidence of benefit.

The guideline discloses potential conflicts of interest for several panel members related to research funding, consulting roles, or ownership of stock in pharmaceutical companies. Management strategies were implemented to mitigate these potential conflicts, such as limiting involvement in discussions of specific products.

This clinical practice guideline provides a comprehensive and detailed overview of the evidence related to vitamin D supplementation for the prevention of various diseases. It leverages a systematic review of existing literature and utilizes the GRADE methodology to formulate recommendations, enhancing the rigor of the guideline. The guideline appropriately acknowledges the limitations of the evidence base and identifies areas for future research. However, the lack of clear benefit for many outcomes, combined with the complexities of vitamin D metabolism and influence of various factors, highlights the need for nuanced interpretation of the findings.