Vitamin A, one of the essential fat-soluble nutrients, plays an important role in your visual, bone, cellular and immune system health. You need minute amounts daily to maintain adequate vitamin A levels in your body. However, it is a fat-soluble vitamin that stores for long periods in your liver. Therefore, too much can cause acute or chronic toxicity, resulting in liver problems.
Vitamin A Compounds
Varying retinoid and carotenoid compounds make up vitamin A. The retinoids include retinol, retinal, and retinoic acid, which generally come from animal sources as preformed vitamin A. The retinoid compounds are the most active or potent form of vitamin A and too much in your body may cause toxicity. Carotenoids come from fruits and vegetable sources as provitamin A and include beta-carotene, alpha-carotene or beta-cryptoxanthin. The carotenoids are not as potent as the preformed retinoids, making toxicity from excess consumption less likely. Your body stores and absorbs retinoid compounds more efficiently than carotenoids. But, the carotenoids serve a significant purpose as antioxidants for immune system health to protect your cells from harmful free radical molecules.
Liver Functions and Vitamin Storage
The gatekeeper and filtration system of nutrients or toxins you ingest is regulated by your liver. A network of blood vessels connects the liver to your digestive tract, and each time you consume food or beverages, your liver produces and then excretes bile to your gall bladder for short-term storage. The gall bladder releases the bile to your pancreas, and then to the intestines to break down fat molecules carrying nutrients in your fat cells including vitamin A. The vitamin A your body does not use remains stored in the liver for up to two years until called upon by your cells for various functions.
Hypervitaminosis A and Toxicity
Too much preformed vitamin A in your body can result from short-term high dose intake or chronic vitamin A exposure, which is referred to as hypervitaminosis A. Correcting this problem simply involves cessation of vitamin A intake. However, significant liver damage may result in the event of chronic vitamin A toxicity. Consumption of natural food sources of vitamin A rarely leads to toxicity with the exception of consuming animal livers, which have a high concentration of active retinol. A 2006 case report published in the "Annals of Hepatology" indicates excess exposure to vitamin A causes your liver to protect itself by forming a fibrotic, or scar tissue, which then sets off a chain of events activating abnormal liver cell formations.
Recommended Intake and Sources
The recommended daily allowance for preformed vitamin A in adult females is 700 mcg, and for adult males it is 900 mcg. Preformed vitamin A sources include eggs, with 89 mcg to 91 mcg per serving, and dairy, with 68 mcg to 100 mcg per cup. Foods like chicken or beef liver exceed the daily recommendation significantly, yielding 7,800 mcg to 22,000 mcg per 3 oz. serving. Provitamin A food sources include carrots, sweet potatoes, broccoli, mango or cantaloupe, with 60 mcg to 961 mcg per 1/2 cup serving. Many supplemental forms of vitamin A contain portions of preformed and provitamin A exceeding the recommended daily dose, but remaining under the tolerable upper limit dose of 2,000 mcg.
References
- Linus Pauling Institute: Vitamin A
- California Pacific Medical Center: How the Liver Works
- Annals of Hepatology; Vitamin A Toxicity in a Physical Culturist Patient; A Case Report and Review of the Literature; Gustavo Castano et al; 2006
- MedlinePlus: Hypervitaminosis A
- Hepatitis Foundation International: Caring for Your Liver
- Office of Dietary Supplements: Vitamin A and Carotenoids
