WASHINGTON: US scientists have developed a way to breed corn that can boost the vitamin A it gives people who eat it - a potentially important advance for regions of the world burdened by vitamin A deficiencies.

Vitamin A deficiency is an important cause of eye disease and other health problems in developing countries. Corn, also known as maize, is the dominant subsistence crop in much of Latin America and sub-Saharan Africa, where up to 30% of children under age 5 are vitamin A deficient.

Scientists want to come up with ways to increase - or "bio-fortify" - levels of specific nutrients in crops like corn. Corn has precursors to vitamin A - compounds called "provitamins" including beta-carotene - which the body uses to make vitamin A.

Writing on Thursday in the journal Science, the scientists identified a naturally mutated gene that enhances the provitamin A content of maize. Based on this, they developed an inexpensive way to select the parent stock for breeding corn with the highest provitamin A content.

Choosing varieties that have this mutated gene can provide on average three-fold higher levels of provitamin A, the researchers said.

There are thousands of different corn varieties, and they differ greatly in provitamin A levels, the scientists said. White corn does not have provitamin A, but yellow varieties have it in varying levels.

A common technique to assess provitamin A content of corn varieties is very expensive for plant breeders, the researchers said, but the new one is vastly cheaper.

"We've come up with a way to detect varieties that will produce high levels of provitamin A inexpensively," said one of the researchers, Edward Buckler of the US Department of Agriculture. Buckler added the method does not involve the genetic modification of corn.