Can you have too much Retinol?

Hypervitaminosis A occurs when the maximum limit for liver stores of retinol is exceeded. The excess enters circulation causing poisoning.

Effects:

birth defects
liver problems,
reduced bone mineral density that may result in osteoporosis
coarse bone growths
hair loss
excessive skin dryness/peeling

Symptoms of an overdose

If you take in too much Retinol you would experience signs of poisoning including nausea and vomiting, headache, dizziness, blurred vision, and loss of muscular coordination.

Although hypervitaminosis A can occur when large amounts of liver are regularly consumed, most cases of vitamin A toxicity result from an excess intake of vitamin A in supplements.

Toxic symptoms can also arise after consuming very large amounts of preformed vitamin A over a short period of time.

Animal Liver

The livers of certain animals, especially those adapted to polar environments, often contain amounts of vitamin A that would be toxic to humans. Thus, vitamin A toxicity is typically reported in arctic explorers and people taking large doses of synthetic vitamin A. The first documented death due to vitamin A poisoning was Xavier Mertz, a Swiss scientist who died in January 1913 on an Antarctic expedition that had lost its food supplies and fell to eating its sled dogs. Mertz consumed lethal amounts of vitamin A by eating the dogs' livers.

Polar bear liver

Just 0.3 grams of polar bear liver contains the upper intake level. If eaten in one meal, 30 to 90 grams is enough to kill a human being, or to make even sled dogs very ill.

Osteoporosis

Excess vitamin A has also been suspected to be a contributor to osteoporosis. This seems to happen at much lower doses than those required to induce acute intoxication.

Lung Cancer

The carotenoid beta carotene was interestingly associated with an increase in lung cancer when it was studied in a lung cancer prevention trial in male smokers. In non-smokers, the opposite effect has been noted.

Vitamin A in pregnancy

Excess vitamin A during early pregnancy has also been associated with a significant increase in birth defects. These defects may be severe, even life-threatening. Even twice the daily recommended amount can cause severe birth defects.

Although Vitamin A is necessary for fetal development, most women carry stores of Vitamin A in their fat cells, so oversupplementation should be strictly avoided.

Recommended supplement limits

The Institute of Medicine has established Daily Tolerable Upper Levels (UL) of intake for vitamin A from supplements that apply to healthy populations, in order to help prevent the risk of vitamin A toxicity. These levels for performed vitamin A in micrograms (µg) and International Units (IU) are:

0-3 years: 600 µg or 2000 IU
4-8 years: 900 µg or 3000 IU
9-13 years: 1700 µg or 5665 IU
14-18 years: 2800 µg or 9335 IU
19+ years: 3000 µg or 10,000 IU

The dose over and above the RDA is among the narrowest of the vitamins and minerals.

Possible pregnancy, liver disease, high alcohol consumption, and smoking are indications for close monitoring and limitation of vitamin A administration. However, vitamin A has also been repeatedly tested and used therapeutically over several decades in larger amounts.