Vitamin A is a fat soluble compound, which means it is stored by the body, mainly in the liver. Because of this, eating the functional form of vitamin A from meat can cause overdose and toxicity. Vitamin A toxicity is very rare, however, mainly because the majority of vitamin A in our diets comes from beta carotene, which is water soluble and therefore regulated and eliminated easily by the body. Symptoms of Vitamin A overdose range from mild side effects like blurred vision or headache, all the way up to permanent liver damage.
The upper limits of Vitamin A is approximately 3,000 ug/day. Exceeding this amount can produce short term and also long term symptoms, the most common of which is liver damage. Toxic overdose of vitamin A most often occurs because of over consumption of the active animal form of vitamin A in the liver of animals. In most situations, only wild or exotic animals can cause toxicity since most domesticated animals have very controlled diets and it takes a extremely large food portion to produce toxic levels. Animals living in cold environments have extremely high levels of vitamin A stored in their livers. For instance, the first reported death from vitamin A overdose was an Arctic explorer who was forced to eat his sled dogs. It has also been estimated that one large bite of the liver of a polar bear would be lethal to a human being. For this reason, the liver of most non-domesticated animals should not be eaten, especially animals living in cold environments.
There are many short term symptoms that can occur immediately following a meal that is extremely high in vitamin A. These symptoms include nausea, blurred vision, headaches and vomiting. A more prolonged instance of vitamin A overdose can produce symptoms like weight loss, fatigue and mental confusion. These symptoms reverse themselves if more appropriate levels of vitamin A are consumed following the overdosed meals. Also, it is important to note that these symptoms are only caused by the animal active form of vitamin A, not from beta carotene, which is found in fruits and vegetables.
Long term or chronic Vitamin A overdose will lead to much more serious symptoms and damage. Some of the symptoms of long term overdose of vitamin A include hair loss, muscle pain and altered personality and mental status. The most serious damage of vitamin A overdose is liver damage, which is both permanent, and often times lethal. The liver damage will often lead to the symptoms of jaundice, fever and chronic diarrhea.
Osteoporosis has also been shown to be caused by excessive vitamin A consumption that is below the overdose levels (3000 ug/day). This is mostly likely the result of the excess vitamin A interfering with the proper function of vitamin D in building bones. The effects of osteoporosis include much higher than normal chances for broken bones during minor trauma.
Increased levels of vitamin A during early pregnancy have also been linked with birth defects, which are often severe and cause the death of the fetus. Again, along with other toxicity and overdoes issues with vitamin A, the problem caused by vitamin A during pregnancy is only from the over consumption of the active, animal source form of vitamin A. Vitamin A from beta carotene which comes from plants does not cause the issues with pregnancy and birth defects. It is important to note that the levels of vitamin A from animals that can result in birth defects is much lower than the toxic levels of 3000ug/day. In the case of fetal birth defects, merely double the recommended daily allowance of vitamin A can cause issues if all of that vitamin A comes from animal sources.
Vitamin A overdose and toxicity is mainly caused by the overconsumption of the animal form of vitamin A. Short term symptoms include blurred vision, headaches, and nausua. In cases of prolonged or extreme overdosing, toxicity will result in permanent liver damage. Women who are pregnant, or want to become pregnant should make sure that their vitamin A comes mainly through beta carotene, as the pure form of vitamin A can cause fetal birth defects at even most overdose levels.