In the early 20th century, children in the United Kingdom were experiencing high incidents of a developmental disorder. Rickets, a condition affecting bone growth and strength, was so prevalent it came to be known as “the English Disease.” The King’s College for Women in London, which happened to have male faculty, tasked biochemist and nutritionist Edward Mellanby with figuring out the cause and potential cure for this disease.
In his experiments, Mellanby decided to feed dogs a diet of oatmeal — one which matched that of the Scottish people — who happened to have the highest incidents of rickets in the U.K. As expected, the dogs developed rickets. To cure them, Mellanby used cod liver oil, and sure enough, it worked. But what was it in the oil specifically that healed this disease?
Another professor, Elmer McCollum of Johns Hopkins, would figure that out.
Some in the academic community believed it was vitamin A within the cod liver oil which cured rickets. By oxidizing the cod liver oil, effectively destroying the vitamin A, McCollum tested whether the preparation would work. When it did, he correctly concluded the substance within cod liver oil curing rickets was a new vitamin altogether; he and his colleagues named it vitamin D.
Interestingly enough, coinciding with the discoveries of McCollum and Mellanby, a physician in Vienna named Huldshinsky, along with Chick and colleagues from England, found that children suffering from rickets could be cured by exposure to summer sunlight or artificially produced UV light.
A fuller understanding of the structure and function of vitamin D would come courtesy ofa study from Askew et al., 15 years later. Based on these findings, in the 1930s, vitamin D was added to milk, a drink routinely consumed by children, in an effort to eradicate rickets.
What’s in a name?
Vitamin D isn’t really a vitamin at all, it’s a hormone. Cholecalciferol — commonly called vitamin D — is a steroid hormone, synthesized via UVB exposure from 7-dehydrocholesterol, a type of cholesterol universally present in the skin. Vitamin D can also come from dietary sources, through supplements or fortified foods, like milk.
Vitamin D is critical for calcium absorption, reduction of inflammation and regulating cell growth, neurological, muscular, and immune function, as well as glucose metabolism. These dual roles in inflammation and immune function likely led clinicians and academics to, once again, look into vitamin D levels in another disease, Covid-19.
Leading the charge was the University of Chicago and David Meltzer, MD, PhD. Data from the University of Chicago Medical Center provided some of the earliest evidence to support the hypothesis that vitamin D deficiency may affect Covid-19 risk. Patients with untreated vitamin D deficiency were 77% more likely to test positive for Covid-19 than patients who were not likely deficient.