Hypervitaminosis A

Forms of preformed vitamin A in the body
Cod liver oil, a potentially toxic source of vitamin A. Hypervitaminosis A can result from ingestion of too much vitamin A from diet, supplements, or prescription medications.

Hypervitaminosis A refers to the toxic effects of ingesting too much preformed vitamin A (retinyl esters, retinol, and retinal).

- Hypervitaminosis A
Forms of preformed vitamin A in the body

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Retinol

Vitamin A

Fat-soluble vitamin and an essential nutrient for humans.

Fat-soluble vitamin and an essential nutrient for humans.

Retinol
Typical location of Bitot's spots
Carrots are a rich source of beta-carotene
Vitamin A supplementation coverage rate (children ages 6–59 months), 2014
Retinoids: Tretinoin is all-trans-retinoic acid; initial tradename: Retin-A. Isotretinoin is 13-cis-retinoic acid; initial tradename: Accutane. Etretinate and Acitretin, its non-esterified metabolite, are used orally to treat severe psoriasis.
Vitamin A biosynthesis from β-carotene
β-ionone ring
Frederick Gowland Hopkins, 1929 Nobel Prize for Physiology or Medicine
George Wald, 1967 Nobel Prize for Physiology or Medicine

Vitamin A toxicity also referred to as hypervitaminosis A, occurs when there is too much vitamin A accumulating in the body.

Methane, CH4; is among the simplest organic compounds.

Β-Carotene

Organic, strongly coloured red-orange pigment abundant in fungi, plants, and fruits.

Organic, strongly coloured red-orange pigment abundant in fungi, plants, and fruits.

Methane, CH4; is among the simplest organic compounds.

When plasma retinol is in the normal range the gene expression for SCARB1 and BC01 are suppressed, creating a feedback loop that suppresses absorption and conversion.Because of these two mechanisms, high intake will not lead to hypervitaminosis A.

The human eye of the right side of the face, showing a white sclera with some blood vessels, a green iris, and the black pupil

Blurred vision

Ocular symptom where vision becomes less precise and there is added difficulty to resolve fine details.

Ocular symptom where vision becomes less precise and there is added difficulty to resolve fine details.

The human eye of the right side of the face, showing a white sclera with some blood vessels, a green iris, and the black pupil

Hypervitaminosis A: Excess consumption of vitamin A can cause blurred vision.

Retinol

Retinol

Fat-soluble vitamin in the vitamin A family found in food and used as a dietary supplement.

Fat-soluble vitamin in the vitamin A family found in food and used as a dietary supplement.

Retinol
Prevalence of vitamin A deficiency in 1995
Vitamin A biosynthesis
β-ionone ring
George Wald, 1967 Nobel Prize for Physiology or Medicine

High doses may cause enlargement of the liver, dry skin, and hypervitaminosis A.

Mawson in 1914

Douglas Mawson

Australian geologist, Antarctic explorer, and academic.

Australian geologist, Antarctic explorer, and academic.

Mawson in 1914
Mackay, David and Mawson raise the flag at the South Magnetic Pole on 16 January 1909
Mawson rests at the side of his sledge, Adelie Land, Antarctica, 1912.
Photo of Douglas Mawson's sledge
Mawson in 1914
Mawson in 1926
Caricature by Sir David Low
Bust of Mawson on North Terrace, Adelaide, South Australia in front of the University of Adelaide
The Mawson Laboratories at the University of Adelaide.

With six dogs between them (with a liver on average weighing 1 kg), it is thought that the pair ingested enough liver to bring on a condition known as hypervitaminosis A.

Carrying the mail and the weekly Klondike Nugget, this service covered all the creeks adjacent to Dawson City. The service was established by Jean (or Gene) Allen in 1898

Sled dog

Dog trained and used to pull a land vehicle in harness, most commonly a sled over snow.

Dog trained and used to pull a land vehicle in harness, most commonly a sled over snow.

Carrying the mail and the weekly Klondike Nugget, this service covered all the creeks adjacent to Dawson City. The service was established by Jean (or Gene) Allen in 1898
A sled dog team of 11 in Denali National Park and Preserve
Huskies ready to ride at the husky farm in Kuusamo, Finland
Point of view of a park ranger driving a six-dog team on Wonder Lake
Sled dog wearing harness during the Jesup Expedition in Siberia
Dog sledding is still commonly used for transportation in parts of Greenland
Labrador huskies being fed by Inuit
A Native American sled dog team of three near Fort Clark, North Dakota, sketched in 1833
US mail carrier and dog sled team arriving at Seward, ca 1912
Caption reads "Ready for The Long Mush, Seward, Alaska" (click photo for further information) ca 1914
A sled dog team of six white huskies hiking in Inuvik, Canada
Col. Ramsay's entry, winning dog sled team of the 3rd All Alaska Sweepstakes, John Johnson, driver ~ c 1910
Musher and dogs enter Iditarod finish chute
Roald Amundsen's Antarctic expedition
Roald Amundsen, whose Antarctic expedition was planned around 97 sled dogs
An Alaskan husky
Sled dog (Alaskan Husky)
An Alaskan Malamute
A Canadian Eskimo Dog
A Chinook
A Greenland Dog
Labrador Huskies
A MacKenzie River Husky
A Samoyed
Stuffed Sakhalin Husky "Jiro" on display
Two Siberian Huskies in harness
Yakutian Laika
Gunnar Kaasen with Balto

Unfortunately eating the liver of sled dogs produces the condition hypervitaminosis A because canines have a much higher tolerance for vitamin A than humans do.

Polar bear

Hypercarnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses.

Hypercarnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses.

Polar bears have evolved adaptations for Arctic life. For example, large furry feet and short, sharp, stocky claws give them good traction on ice.
Bears investigate the submarine USS Honolulu 280 mi from the North Pole
Polar bear jumping on fast ice in Spitsbergen Island, Svalbard Archipelago, Norway
Subadult males frequently play-fight. During the mating season, actual fighting is intense and often leaves scars or broken teeth.
The polar bear's long muzzle and neck help it to search in deep holes for seals, while its powerful hindquarters enable it to drag massive prey
Bear feeding on a bearded seal
Cubs are born helpless and typically nurse for two and a half years
Mother and cub on Svalbard, Norway
Skins of hunted bears
Road sign warning about the presence of bears. The Norwegian text translates into "Applies to all of Svalbard".
Dogsleds are used for recreational hunting of polar bears in Canada
Polar bear in Denver Zoo.
Map from the U.S. Geological Survey shows projected changes in polar bear habitat from 2001 to 2010 and 2041 to 2050. Red areas indicate loss of optimal polar bear habitat; blue areas indicate gain.
Mothers and cubs have high nutritional requirements, which are not met if the seal-hunting season is too short
Starving bear near Svalbard
Swimming
Engraving, made by Chukchi carvers in the 1940s on a walrus tusk, depicts polar bears hunting walrus
Greenland's 1911 five kroner note depicting a polar bear

The resulting high concentrations cause hypervitaminosis A, Hunters make sure to either toss the liver into the sea or bury it in order to spare their dogs from potential poisoning.

Mertz at the expedition's main hut, 1912

Xavier Mertz

Swiss polar explorer, mountaineer, and skier who took part in the Far Eastern Party, a 1912–1913 component of the Australasian Antarctic Expedition, which claimed his life.

Swiss polar explorer, mountaineer, and skier who took part in the Far Eastern Party, a 1912–1913 component of the Australasian Antarctic Expedition, which claimed his life.

Mertz at the expedition's main hut, 1912
Mertz exploring ice ravines near Cape Denison
Mertz on the ice cliff near the base
Last photograph taken of the Far Eastern Party
Memorial cross erected at Cape Denison

The cause of Mertz's death has never been firmly established; the commonly purported theory is hypervitaminosis A—an excessive intake of vitamin A—from consuming the livers of the Huskies.

Route from Cape Denison across the Mertz and Ninnis Glaciers,

Far Eastern Party

Sledging component of the 1911–1914 Australasian Antarctic expedition, which investigated the previously unexplored coastal regions of Antarctica west of Cape Adare.

Sledging component of the 1911–1914 Australasian Antarctic expedition, which investigated the previously unexplored coastal regions of Antarctica west of Cape Adare.

Route from Cape Denison across the Mertz and Ninnis Glaciers,
Last photo of the Far Eastern Party, 17 November 1912
Mawson at Aladdin's Cave during the outward journey
"We could do nothing," wrote Mertz in his diary after Ninnis' death. "We were standing, helplessly, next to a friend's grave, my best friend of the whole expedition."
Mertz at Cape Denison
Mawson's half sledge, which he used during the final stage of the journey
Mawson shortly after his return to Cape Denison
Memorial cross erected at Cape Denison

The causes of Mertz's death and Mawson's related illness remain uncertain; a 1969 study suggested hypervitaminosis A, presumably caused by the men eating the livers of their Greenland huskies, which are now known to be unusually high in vitamin A.

Novaya Zemlya's west coast as depicted in De Veer's diary

Gerrit de Veer

Gerrit de Veer (c.

Gerrit de Veer (c.

Novaya Zemlya's west coast as depicted in De Veer's diary

De Veer kept a diary of the voyages and in 1597, was the first person to observe and record the Novaya Zemlya effect, and the first Westerner to observe hypervitaminosis A caused by consumption of the liver of a polar bear.