Vitamin D has been the focus of tremendous ongoing scientific research during the past two decades. Its undisputed role in bone mineralization has been expanded to a disparate set of scientific cases and observational studies, randomized controlled trials of doubtful design, and sporadically personal aphorisms and dogma. This phenomenon is a burgeoning scientific field in which substantial controversy is inevitably reflected in daily clinical practice resulting in a precarious interpretation of not necessarily available results, lifestyle-affected vitamin D supplementation in vitamin D sufficient populations, and ineffective dosing and time regimens.

In this context, the vast majority of healthcare providers worldwide involved in some part of the developed vitamin D daily agenda suggest a sound individualized scientific approach unbiased from quandaries, oriented to improve long-term health outcomes and patient quality of life, beyond the available knowledge in the field.

This Special Issue will draw attention to all intriguing and conflicting aspects of vitamin D research, including vitamin D deficiency and its widespread epidemiology, musculoskeletal and extra-skeletal effects, and critical updates on published vitamin D supplementation prevention RCTs (cancer/CVD). The aim is to present a discourse on the future agenda with the main questions: what has changed so far in the field, and what are the future research milestones?

Potential topics include but are not limited to the following:

• Vitamin D and nutritional rickets: current and future perspectives and policies around the world
• The role of vitamin D in upper respiratory infections
• Epidemiology of hypovitaminosis D worldwide
• Cardiovascular disease and vitamin D: what have we learned from recent vitamin D mega-trials?
• The role of hypovitaminosis D in osteomalacia: current clinical practice and future research agenda
• Vitamin D and chronic pain
• Transcriptional regulation and actions of vitamin D in muscle tissue
• Vitamin D fortification strategies: a non-interventional approach
• The role of vitamin D in atopic diseases: pathophysiology and management
• The role of vitamin D in preventing type 2 diabetes in individuals with prediabetes
• Vitamin D and type 1 diabetes
• Vitamin D supplementation and cancer