BACKGROUND

1. Percentage of vitamin A stores that are drained per day when on a diet without Vitamin A (0,05 %).

2. Maintenance of a minimum reserve of vitamin A in the liver (20 µg/g).

3. Liver weight:body weight ratio (1:33)

4. Reference weight for a certain age and gender (61 kg for women and 76 kg for men)

5. Total content of vitamin A in the body:vitamin A in the liver (10:9)

6. Storing efficiency (40 %).

A minimum liver reserve is set at 20 µg/g as it with this level is not associated with any clinical symptoms of vitamin A deficiency, gives adequate plasma retinol concentration, and protects against vitamin A deficiency for 4 months on a vitamin A free diet.

From this we can estimate the following average requirement (estimated average requirement, EAR):

0,005 x 20 µg/g x 0,03 x 61 kg x 1,1 x 2,5 = 503 µg for a woman weighing 61 kg, and 627 µg for a man weighing 76 kg.

By multiplying the average daily requirement (EAR) with two standard deviations (2 SD) the new value would cover the need of approximately 97,5 % of the population, giving what is called a recommended dietary allowance (RDA).

Since the standard deviation is most often not known it is common to set the variation to 10 %, adding 2 x 10 % on the avarage requirement.

This results in a recommended daily intake of 700 µg for women and 900 µg for men.

This means a reduction in the recommended daily intake for women from 800 µg in the old recommendations (1996) to 700 µg in the latest recommendations.