An adequate intake of vitamins is essential for good health, but too many vitamins can be as harmful as a vitamin deficiency. The medical term for excessive levels of vitamins in the body is “hypervitaminosis.” Hypervitaminosis A, or too much vitamin A, is usually caused by the overuse of dietary supplement tablets.
Functions of Vitamin A (Retinol) and Daily Vitamin Requirements
Among various other functions, vitamin A (also known as retinol) is used to synthesize light-absorbing molecules found in the retina of the eye. It is therefore important for good vision, and an inadequate intake can lead to impaired vision, damage to the eye or even blindness. Liver is rich in vitamin A, while orange or yellow vegetables and fruits contain a substance called beta carotene that is converted into vitamin A in the body.
The US Institute of Medicine’s recommended daily allowance (RDA) for vitamin A in adults is 900 micrograms per day (μg/day) for men and 700 μg/day for women. The upper limit for vitamin A intake, which was introduced to help prevent overdosing, is 3,000 μg/day for both men and women. A regular intake significantly higher than this carries a risk of hypervitaminosis A.
Signs of Overdose of Vitamin A
Although it is possible to overdose on vitamin A by eating excessive amounts of liver, most cases are caused by accidental or intentional overuse of dietary supplements. Vitamin A toxicity can be acute (due to a short episode of overdosing) or chronic (caused by overdosing over a long period of time) and has many possible effects, including:
- blurred vision
- nausea
- headache
- drowsiness
- poor coordination
- skin and hair problems such as angular cheilitis, itchy, peeling skin and hair loss
- liver or kidney damage
- birth defects and poor weight gain in infants.
Eating large amounts of carrots can turn the skin yellow, but beta carotene is non-toxic and is not thought to pose any health risks.
Treating Vitamin A Toxicity
Hypervitaminosis A is treated by simply stopping taking supplements. Most people recover fully after returning to their RDA for vitamin A, obtained by eating a healthy, varied diet. In some cases of long-term vitamin A overdosing, treatment for liver and/or kidney damage is required.
References:
Hypervitaminosis A. Accessed 24-11-10
Vitamin A and Carotenoids. Accessed 24-11-10
Disclaimer: The information contained in this article is for educational purposes only and should not be used for diagnosis or to guide treatment without the opinion of a health professional. Any reader who is concerned about his or her health should contact a doctor for advice.
