Historically, rickets was among the earliest diseases to be described. As early as 300 B.C., Lu-pu-wei described crooked legs and hunchback; however, these can occur with other disorders. More specifc references are found in the separate writings of three Chinese physicians of the seventh and eighth centuries A.D., including enlarged head, body wasting, pigeon breast, and delayed walking. By the tenth century, Chien-i, the Father of Chinese pediatrics, described many cases of rickets (Lee 1940).

In the second century A.D., Soranus of Ephesus mentioned characteristic deformities of the legs and spine in young children and remarked on the higher frequency in urban Rome compared to Greece. Slightly later, Galen's work included a description of skeletal deformities in infants and young children, particularly the knock-knee, bow leg, and funnel-shaped chest, and pigeon breast seen in rickets. Sporadic and somewhat ambiguous references to the disease were made until the mid-seventeenth century, when the classic descriptions of Daniel Whistler and Francis Glisson appeared.

In 1645 Whistler published his medical thesis in Latin, On the Disease of English Children which is Popularly Termed the Rickets. Five years later, Glisson wrote the classic text on the subject, still unsurpassed as a clinical description of rickets. Both physicians considered the disorder of recent origin, and indeed the northern climate, crowded living conditions, and socioeconomic changes may have influ enced its prevalence at that time. Glisson himself noted a number of cases affecting the "cradles of the rich," perhaps related to the use of swaddling clothes and the vitamin D-deficient diet of pap and starch.

The word "rickets" was first used in the London Bill of Mortality report for 1634. The derivation of the word has been a source of contention since that time. Possibilities include rucket in Dorset dialect, meaning "short of breath"; the verb rucken, meaning "to rock or reel"; the Middle English word wricken, denoting "to twist"; the Saxon word rick, meaning "heap" or "hump"; or the Norman word riquets, for hunchback. Glisson suggested the term "rachitis" derived from the Greek word for spine, and this term remains in use in many countries today.

Nearly 250 years passed before the specific role of vitamin D and its active metabolites was elucidated via biochemical studies. L. Findlay (1908) reproduced the disease in puppies raised in a confined, darkened space. A year later, Georg Schmorl (1909) demonstrated the striking seasonal variation of the disease by autopsy findings. In 1917 Alfred F. Hess and L. J. Unger described the prevention of rickets by use of cod liver oil or by ultraviolet irradiation. Shortly thereafter, a number of researchers, particularly the group of Elmer V. McCollum (1922), isolated vitamin D and related compounds. A better understanding of the exact mechanisms and conversion of vitamin D metabolism into more active forms was gained only since the mid-1960s and 1970s (Lund and DeLuca 1966; Fraser and Kodicek 1970).

Vitamin D is classified more accurately as a prohormone rather than a vitamin. It is formed by the interaction of ultraviolet light with a cholesterol derivative in the deeper layers of the skin, but small amounts of vitamin D may also be derived from dietary sources such as dairy product and fish liver oils. Vitamin D is then hydroxylated once in the liver, and a second hydroxylation into the highly active hormone occurs in the kidney. It acts upon the target organs, intestine, and bone to regulate serum calcium and phosphate levels and the mineralization of bone.

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