Science - April 8, 2010

Inactive enzyme raises need for vitamin A

An extra helping of carrots or a vitamin A pill now and then may be what many people need. This conclusion can be drawn from the research findings of postdoc student Yvonne van Helden of the Human and Animal Physiology chair group, published this week in Cellular and Molecular Life Sciences.

Van Helden used special laboratory mice with a vitamin A metabolism which resembles that of humans. Although the animals were given a diet with sufficient vitamin A, they developed deficiency symptoms. Van Helden thinks that this is because the animals do not have the enzyme BCMO1 which converts beta-carotene into vitamin A. The entire vitamin A metabolism is thus turned upside down. Surprisingly, these deficiency symptoms did not show up when the animals were fed extra beta-carotene. 'So it seems that beta-carotene is converted into vitamin A, but in another manner', concludes van Helden. 'Reduced BCMO1 activity appears to be coupled with changes in Vitamin A metabolism.'
Since the conversion of beta-carotene in many laboratory animals progresses differently from that in humans, very few experiments have been conducted on this substance. The appearance of 'human' mice will pave the way towards more insight into vitamin A. The fact that the mice needed more vitamin A than expected could also imply that the same goes for humans, postulates Van Helden. The working of the BCMO1 enzyme differs from person to person. 'In 27 to 45 percent of the population, this enzyme is not so active', she explains. 'As such, these people, just like the 'human' mice, could suffer from vitamin A deficiency now and then. Vitamin A deficiency is often seen as a problem in developing countries, which leads to their populations being more vulnerable to infections. According to Van Helden, this deficiency in the western world is possibly more widespread than thought, especially in people with a less active BCMO1 enzyme. And yet, she recommends putting aside that bottle of vitamin A pills for the time being. 'Studies have shown that a high dose of vitamin A can be harmful for the health. We don't know what the right dose is at this moment.'