By Richard Black
BBC environment correspondent
UK scientists have developed a new genetically modified strain of "golden rice", producing more beta-carotene.
The new strain of golden rice has far more beta-carotene
The human body converts beta-carotene into vitamin A, and this strain produces around 20 times as much as previous varieties.
It could help reduce vitamin A deficiency and childhood blindness in developing countries.
The World Health Organization estimates up to 500,000 children go blind each year because of vitamin A deficiency.
When the original strain of golden rice emerged from laboratories in Switzerland five years ago, it was hailed by some as an instant solution.
But that original strain did not produce enough beta-carotene to ensure that children would get their daily requirement from eating normal quantities of rice.
And because of concerns about GM agriculture, it still has not been grown in field trials in Asia.
The new variety, developed at the UK laboratories of the biotechnology company Syngenta, produces much more beta-carotene.
Syngenta is making the rice available for free to research centres across Asia, who will, if they are given the go-ahead by their governments, begin field trials - probably within the next five years.
Not everyone believes golden rice is the best answer to Vitamin A deficiency.
Some agricultural experts and environmental groups say aiming for a balanced diet across the board would be a better solution.
"The problem is that you're trying to fix vitamin A deficiency with a narrow GM solution when the problem is much more complex," said Clare Oxborrow, from the anti-GM group Friends of the Earth.
"People who are deficient in vitamin A are also deficient in a whole host of other vitamins and minerals. What are we going to do? Are we going to genetically modify a crop to address these issues, too?
"What we should be doing is trying to support people to grow the diverse types of food that meet all their nutritional needs."
However, the Golden Rice Humanitarian Board, which is overseeing developments in the plant technology, said the crop was not intended to be the sole solution.
It said malnutrition was rooted in political, economic and cultural issues that could not be magically resolved by a single agricultural technology.
"We are trying to deal with part of the problem; we are not against supplementation, fortification, [or] small house gardens," explained Dr Jorge Mayer, the golden rice project manager.
"All this has been tried for many years and still, with all the existing programmes, with millions of dollars being invested every year - there is still a gap to be filled.
"We believe we can fill a gap and with the other programmes to try to achieve full coverage."
The latest scientific research is published in the journal Nature Biotechnology.