Vitamin D (ergocalciferol) is used during convalescence primarily based on scientific evidence. Convalescence refers to the period of recovery after illness, injury, or surgery, during which the body repairs and regains strength. Scientific studies have demonstrated that vitamin D plays a key role in immune modulation, muscle function, and bone health—all of which are relevant to recovery processes. Deficiency in vitamin D is associated with increased risk of infections, impaired muscle function, and delayed wound healing, which can complicate or prolong convalescence.

Several clinical guidelines recommend monitoring and correcting vitamin D deficiency in patients recovering from major illnesses, especially in populations at risk (elderly, those with limited sunlight exposure, or with malabsorption). Some randomized controlled trials and observational studies support supplementation to reduce the risk of infections, improve muscle strength, and possibly shorten hospital stays, although data are not wholly consistent and most benefits are observed in those who are deficient. The evidence is strongest for supporting musculoskeletal recovery and immune health, rather than for direct acceleration of convalescence per se.

In summary, while vitamin D supplementation is not universally indicated for all convalescent patients, addressing deficiency during recovery is backed by moderate scientific evidence and is supported by its physiological roles. The overall evidence base rates as moderate (3/5), especially in populations with documented deficiency.