Although retinol's supporting evidence is weaker than that of its cousin, retinoic acid, it may still help to push out lines.

Others have dismissed such views as alarmist, saying there is little supporting evidence.

But it has also in the past declared plants to be nuclear without any clear supporting evidence, apparently hoping that it would embarrass the clerical regime.

Entrants must supply supporting evidence where necessary to prove that this work is underway.