In the 1600s in England, physicians noticed that more and more young children had deformed bones. So many children were affected it was called “The English Disease.” Later, the condition was named rickets.
Rickets Associated with Industrialization
As more countries became industrialized, more children were affected, especially children in poor families and those in more northern regions. Industrialization led to soot and smog in the air, and to urban living, away from the sunny open fields for children’s play. In North America especially, industrialization occurred more in northern latitudes, where sunny days are less frequent, and where the earth tilts further away from the sun in winter. All those factors led to less sun exposure for children. Rickets was noted to be associated with low sun exposure.
Cod Liver Oil Found Beneficial
In the 1800s, cod liver oil, high in both vitamins A and D, was suggested as a remedy. Lion cubs in the London Zoo had the condition, but got better when fed bone meal (calcium) and cod liver oil, further sealing knowledge of the benefits of cod liver oil. But it was not until the 1930s that vitamin D was named as the beneficial ingredient of cod liver oil. (Kumaravel Rajakumar: Pediatrics 2003;112;e132-e135. DOI: 10.1542/peds.112.2.e132)
Folklore had also suggested sun exposure to prevent or treat rickets. It turns out both cod liver oil and sun exposure do the same thing: increase vitamin D in the body. Rickets can be prevented and treated by vitamin D.
What Is Vitamin D?
“Vitamin D” refers to two substances, vitamin D2 and vitamin D3. Most sources say the two, D2 and D3, are equally potent. Vitamin D is all but one link short of being a steroid; its B ring is broken. Vitamin D, both D2 and D3, are produced by photolysis—exposure to light, especially ultraviolet B. Since it can be made in the skin, it can rightfully be called a hormone.
It’s the manufacture of a precursor vitamin D in the skin where sunlight comes into play. A steroid substance in the skin, when exposed to uV-B, is converted into precursor vitamin D. This process depends on the intensity of sunlight. In skin with more melanin, which filters sunlight, the process takes longer. However, melanin does not put a limit on the amount of vitamin D precursor made; it just makes it take longer. When adequate precursor is made, the system shuts down, so too much vitamin D won't be produced.
Fur also blocks sunlight. Dogs and cats produce precursor substances in skin glands. The substances reach the surface of the fur where sunlight can convert them to vitamin D precursor. The animal consumes the irradiated substance when it licks its fur. So the cat, licking its fur, is not only grooming, she’s getting a nutritional supplement.
A vitamin D precursor can also come from the diet. Whether the vitamin D precursor comes from the skin or food, it must undergo two more steps to be active, one step in the liver and one in the kidneys.
Where and How Activated Vitamin D Works
It acts just like any hormone. Active vitamin D travels in the blood, and docks on specific cell receptors, VDRs. These VDRs are on the nuclei of cells of bones, intestines, cardiovascular system, brain, gonads, prostate and breasts.
- The most is known about vitamin D’s bone-related activity. It increases the absorption of calcium in the intestines, and controls the loss of calcium in the kidneys. It increases the rate of bone turnover, which usually produces new bone.
- In the cardiovascular system, low vitamin D has been associated with high blood pressure and peripheral arterial disease. Higher D levels lowers the risk of these ailments.
- How vitamin D works in the brain is largely unknown. Low vitamin D has been associated with seasonal affective disorder, memory problems and Parkinson’s disease.
- The role vitamin D plays in the prostate, gonads, and breast is largely unknown.
- Vitamin D can retard the growth of cancer cells in the laboratory, but it can also accelerate their growth.
Source:
Greenspan and Gardner: Basic & Clinical Endocrinology, 7th edition. Lange Publishers.
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