Age dating bone fractures
In 1912, Frederick Gowland Hopkins demonstrated that unknown accessory factors found in milk, other than carbohydrates, proteins, and fats were necessary for growth in rats.
Hopkins received a Nobel Prize for this discovery in 1929.
All forms of vitamin A have a beta-ionone ring to which an isoprenoid chain is attached, called a retinyl group.
The orange pigment of carrots (beta-carotene) can be represented as two connected retinyl groups, which are used in the body to contribute to vitamin A levels.
Zinc deficiency can also impair absorption, transport, and metabolism of vitamin A because it is essential for the synthesis of the vitamin A transport proteins and as the cofactor in conversion of retinol to retinal.
Vitamin A deficiency can occur as either a primary or a secondary deficiency.
The findings of the review extend evidence that antioxidants may not have long-term benefits.
The discovery of vitamin A may have stemmed from research dating back to 1816, when physiologist François Magendie observed that dogs deprived of nutrition developed corneal ulcers and had a high mortality rate.
Some of these symptoms are also common to acne treatment with Isotretinoin.
Chronically high doses of vitamin A, and also pharmaceutical retinoids such as 13-cis retinoic acid, can produce the syndrome of pseudotumor cerebri.
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These toxicities only occur with preformed (retinoid) vitamin A (such as from liver).