Rickets 1922 – Nutritional Deficiency and Bowed Legs

Rickets is a childhood disease usually caused by severe, prolonged vitamin D deficiency. It softens and weakens bones, leading to bowed legs and more fractures. 

In the late nineteenth century, British doctors noticed a dramatic increase in rickets as people moved from rural areas to polluted industrial cities. In 1919, a famous study began to understand its causes and develop treatments. British physician Edward Mellanby raised dogs indoors and induced rickets by feeding them a diet containing porridge. He then cured the dogs by giving them fish liver oil and suggested that rickets had a nutritional cause. He thought vitamin A in the oil was probably the essential nutrient.

Shortly after Mellanby's work, American biochemist Elmer McCollum and his colleagues observed that the oil still cured rickets after its vitamin A activity had been destroyed. In 1922, McCollum named this particular component vitamin D. In 1923, other researchers showed that vitamin D formed when its precursor in the skin (7-dehydrocholesterol) was exposed to sunlight or ultraviolet light.

Vitamins are organic substances present in small amounts in natural foods, needed for normal metabolism, and whose dietary deficiency causes disorders. Vitamin D itself (D2 or D3) is not a hormone, because it does not fit the definition of a substance produced in one organ, carried through the blood to another and affecting the activity of a target organ there (the definition of a hormone). In short, because the body can synthesise vitamin D when exposed to sunlight, it can be said that it is not truly considered an essential vitamin but is classified as a group of steroid hormones. Dark-skinned babies require longer sun exposure to produce enough vitamin D. 

• In the body, vitamin D in the bloodstream travels to the liver, where it is converted into a hormone preceding calcidiol. 
• The kidneys or certain white blood cells then convert circulating calcidiol into calcitriol, the biologically active form of vitamin D. 
• When synthesised by white blood cells, calcitriol helps the body's immune system.
• Circulating calcitriol binds to vitamin D receptors (VDRs) in the intestines, bones, kidneys and parathyroid gland, helping establish beneficial calcium and phosphorus levels in the blood and maintain calcium in bones. 
• Vitamin D may reduce calcium levels in bones because of calcium-deficient diets.

Description of the article image: An image of normal legs and legs affected by rickets

Historical figures mentioned in the article: Elmer Verner McCollum (1879–1967), Edward Mellanby (1884 –1955)

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