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This article was published 1/11/2012 (1696 days ago), so information in it may no longer be current.
How much vitamin A are you taking? Not sure? If so, it's prudent to know more about this important vitamin. A report from Tuft's University shows those who take too much of this vitamin will get more than they bargained for. That's why the bear had the last laugh over arctic hunters.
Long before researchers discovered vitamins, ancient Egyptians knew the liver could cure night blindness, the inability to see in low light. Later, Hippocrates prescribed liver soaked in honey for blindness in malnourished children. It's tragic that even today one million children worldwide are blind due to a lack of vitamin A. Adequate amounts of A are needed to prevent this problem and for reproductive health and immune function.
Today, however, due to improved diet from eggs, vegetables and the fortification of milk and cereals, there are only isolated cases of vitamin A deficiency in North America.
Now, the problem is lack of awareness it's possible to take too much of a good thing.
Dr Jeffery K. Griffiths at Tufts University in Boston says, "There is a general belief out there that vitamin A is not only safe in high amounts, but innocuous fundamentally."
But don't try to sell that advice to Arctic hunters. Some unsuspecting hunters tracked down a bear and shot it. Since they all loved liver, they looked forward to a meal of bear's liver and consumed large quantities of it. But, although great hunters, they were babes in the wood when it came to knowing about the vitamin A content of bear liver.
Since bears are carnivores, they eat fish-eating carnivores such as seals, and consume large amounts of vitamin A. But through evolution, they've developed the capacity to store in their livers 3,000 times the recommended daily amount (RDA) needed by humans. This is why the hunters became violently ill with diarrhea, headache, dizziness and jaundice.
But not just hunters develop vitamin A toxicity. For instance, the RDA for adults is 3,000 international units ((IU). But for children, the RDA is just 1,000 to 2,000 IU. Several years ago, one company had to recall its energy bars because they contained 32,500 IU of vitamin A!
One young girl developed increasing fatigue, loss of appetite and finally kidney failure. Her grandmother owned a health-food store and was gradually killing her with excessive vitamin A. Another child developed agitation, fever and pains in her bones due to vitamin A poisoning.
Adults who receive too much vitamin A complain of hair loss, nausea, dry, scaly skin, fatigue, headaches and blurred vision.
So how much is too much? Authorities say chronic toxicity can occur by taking 25,000 IU.
But, in the 1990s, it was discovered even low levels could put people at risk. Women taking the drug Accutane were more prone to having children with birth defects, such as heart problems or cleft palate.
Excessive amounts of vitamin A have also been linked to hip fractures. The Harvard Health Study has followed 120,000 nurses for the last 26 years and reports postmenopausal nurses who consumed 10,000 IU of vitamin A had a 48 per cent greater risk of hip fracture than women who consumed 1,250 IU of vitamin A.
This association has been confirmed by another study in Sweden, where cod liver oil is traditionally used as a natural remedy to prevent disease. In this study, women who consumed 5,000 IU daily had double the number of hip fractures compared to those with intakes of about 1, 650 IU.
The Harvard study also revealed some nurses obtained 40 per cent of their vitamin A from multivitamin tablets. So if you're getting vitamin A this way, be sure to read how many IU's are in the tablet.
The message is not all vitamins play by the same rules. For instance, vitamin C is water-soluble, easily used up, excreted from the body and has no toxic level. But A is fat-soluble, stored and potentially dangerous for hunters and the rest of us.
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