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Top predators in the Arctic are known to accumulate vitamin A, often to levels that are toxic for human consumption. A 2012 study by Senoo, Imai, et al. found that the livers of several predator species in the Arctic showed much higher levels of vitamin A than other Arctic species or closely related continental species, with no symptoms of hypervitaminosis A.

Why is it that these species accumulate vitamin A? Does this have something to do with the food sources available in the Arctic as opposed to the mainland? Or are there physiological reasons why Arctic predators would tend to accumulate vitamin A rather than breaking it down or otherwise eliminating it?

References:

  • Senoo, Haruki; Imai, Katsuyuki; Mezaki, Yoshihiro; Miura, Mitsutaka; Morii, Mayako; Fujiwara, Mutsunori; Blomhoff, Rune (2012). "Accumulation of vitamin A in the hepatic stellate cell of arctic top predators". Anatomical Record 295 (10): 1660–8. doi:10.1002/ar.22555. PMID 22907891.
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  • $\begingroup$ This study seems to be the only research on this particular topic, so no one will be able to provide you a definite answer. The authors suggest the following explanation: "Without huge capacity of storage ofvitamin A in HSCs in the arctic top predators, these ani-mals may suffer from hypervitaminosis A after intake ofthe large amount of vitamin A through the food chain,and cannot stay in the top of the food web there." $\endgroup$ – Hav0k Mar 22 '16 at 14:31
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    $\begingroup$ @Hav0k That "explanation" fails to account for why non-Arctic predators do not store vitamin A at such levels. $\endgroup$ – augurar Mar 23 '16 at 0:09
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    $\begingroup$ It doesn't explicitly state it but the implication is that non-Arctic predators don't have high vitamin A content in their food chain. Many saltwater fish carry high levels of vitamin A. So if this is the primary food source, e.g. seals eat fish, bears eat seals, then you need high tolerance for it. Land animals have less vitamin A, so their predators don't need the tolerance. I can't find any evidence of it but I thought vitamin A helped animals survived the cold, but there are also high concentrations in tuna liver, which are typically temperate or tropical. $\endgroup$ – Nathan Mar 23 '16 at 15:44
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The phytoplankton at the bottom of the food chain have high levels of vitamin A and precursors like beta-carotene. At each step up the chain, vitamin A bioaccumulates. Top predators in the Arctic deal with this by storing the vitamin A in the liver (bears, cetaceans) or blubber (pinnipeds).

This is the same mechanism that causes accumulation of pesticides like DDT in animals. https://en.wikipedia.org/wiki/Bioaccumulation

Carotenoids are part of the photosynthetic system, and also protect the organism from sunlight. Phytoplankton are unicellular, so each cell needs protection. Therefore land plants contain much less carotenoids, since most of the cells are interior and protected from the sun. For example, grains, roots, and wood have very low levels of carotenoids.

This occurs in polar regions due to up-welling nutrient-rich waters supporting high productivity. Temperate and tropical deep ocean regions are typically deserts due to low nutrient levels, particularly iron and fixed nitrogen.

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    $\begingroup$ This answer does not answer the question on the difference between top predators of the arctic area and those of the mainland (or the oceans) closer to the equator, and the question why they do not suffer symptoms of hypervitaminosis A. Regarding the first question, does the phytoplankton in the Arctic area have higher concentration of vitamin A and precursors like beta-carotene? $\endgroup$ – Hans Sep 29 '16 at 18:46

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