Vitamin A (retinol and beta-carotene)

Vitamin A (retinol and beta-carotene)Pure vitamin A (retinol) is a lipid-soluble vitamin. It is primarily found in animal sources that contain fat. Vegetable sources contain a lipid-soluble precursor of vitamin A called beta-carotene. Pure vitamin A is primarily stored in the liver and in fatty tissue, for which reason we do not need a daily supply of the nutrient. Vitamin A and zinc work together. A deficiency in one nutrient will therefore affect the other. On a global scale, vitamin A deficiencies are widespread. In Western countries vitamin A deficiency is normally seen in connection with chronic disease. Vitamin A is destroyed when exposed to oxygen or heat, for instance during cooking.

Functions and importance

Deficiencies and poor utilisation may be caused by:

Deficiency symptoms

A vitamin A deficiency is detectable by means of a blood test that measures the blood content of retinol.

Animal and plant sources

The two most important sources are:

Retinol
Pure vitamin A from animal sources
Beta-carotene
Precursor from plant sources
Found in animal sources such as cod liver oil, liver, liver pate, kidneys, butter, cheese, egg yolk, and oily fish Found in green/red/yellow vegetable sources such as carrots, rosehips, parsley, kale, spinach, tomatoes, bell pepper, and melon.
Lipid-soluble
Stored in the liver and in fatty tissue for future need.
Requires zinc to be released from the liver.
Stays a relatively long time in the body.
Lipid-soluble
Gets converted to retinol in the intestinal mucous membrane as needed.
Does not get stored.
A particularly powerful antioxidant.
The most potent type of vitamin A.
12 times stronger effect than seen with beta-carotene.
Possible to overdose.
The weakest type of vitamin A.
The need is correspondingly greater. Practically impossible to overdose, which makes it safer for supplementation.


Measuring units for retinol and beta-carotene

The content of vitamin A is specified in RE (retinol equivalents) that corresponds with the total vitamin A effect.
Recent studies have shown that the effect of beta-carotene is not as great as previously assumed. For that reason, the vitamin A effect of beta-carotene has been halved in the new food listings.

1 RE= 1 microgram of retinol = 12 micrograms of beta-carotene
The former declaration known as IU (International Units) is still seen.
1 IU = 0.3 micrograms of retinol

Vitamin A content in selected foods (per 100 grams).

The content of retinol and beta-carotene is listed both in micrograms and in RE:

Cod liver oil (retinol)

30,000 micrograms/ RE
Pork liver (retinol) 14,125 micrograms /RE
Carrots (beta-carotene) 9,790 micrograms = 816 RE
Spinach (beta-carotene) 4,186 micrograms = 349 RE


Recomended daily allowance

Adults: 11 years of age and older: 800 micrograms/RE
Children: 1-10 years of age: 400 micrograms/RE.

Supplements are available both with retinol (pure vitamin A) and beta-carotene.

Always remember to take supplements together with a meal, as the fat content increases nutrient absorption.

Increased need

Precautions

Beta-carotene and smokers

Nutritional supplements with beta-carotene must carry a warning stating that these products are not suited for smokers. This warning is a consequence of two American studies that were conducted with synthetically manufactured beta-carotene. When ingested in excessive amounts, this may slightly increase the risk of lung cancer in heavy smokers. In contrast, Chinese research has shown that beta-carotene combined with selenium and vitamin E reduces the risk of lung cancer.

Overdosing and side effects