“To help retain the peak of sunny summer health—to help maintain rugged resistance to winter colds and sickness—drink Schlitz [beer], with Sunshine Vitamin D”, reads an advertisement in the American Magazine from December, 1936.
The fascination with vitamin D supplementation began with the discovery in the early 1920s that vitamin D prevented rickets and was further driven by the recognition of other potential roles of vitamin D in non-skeletal outcomes, including immune function, cardiovascular health, and cancer. However, whereas data on the function of vitamin D in bone growth and maintenance is clear-cut and has informed practical clinical guidelines and public health policies over the years, evidence supporting the role of vitamin D in other health and disease processes, in particular in acute respiratory tract infection, remains patchy. Data from observational studies have suggested that vitamin D supplementation can lower the odds of developing respiratory infections, particularly in vitamin D-deficient groups, but randomised trials have yielded mixed results.

Ragesoss CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], from Wikimedia Commons

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