Night Blindness.

The Ancient Egyptians and Greeks wrote about night blindness, or ‘nyctalopia’. This affliction makes it impossible to see in dim light, and sufferers become completely blind when night falls. The Egyptians found that they could cure sufferers by feeding them liver, which contains high levels of vitamin A, the deficiency of which causes night blindness.

Vitamin A deficiency still affects one third of all children on Earth under the age of five, resulting in over half a million deaths each year. Most high dose vitamins obtain their vitamin A from liver, which is dangerous at high levels and can cause various health complications. In the past, starving Antarctic explorers would eat their dogs for food but became sick when they ate too much liver. Vitamin A found in carrots is a slightly different molecule to that found in liver and is not toxic in high doses, although it can cause skin to turn yellow. During the Second World War, the Allies announced that they ate carrots to see well, although carrots only help maintain normal vision and do not improve it beyond this. Actually they were lying to hide their development of radar.