"The reason that we chose pizza is just because it is a very popular food product, not only in the US but worldwide," said Jeffrey Moore, who worked on the study at the University of Maryland.

The study focused on fermentation time for the dough, baking temperatures, and baking time.

Antioxidant levels rose with higher baking temperatures, depending on the type of wheat flour and the antioxidant test used.

The precise mechanisms involved are unclear, according to the findings of the study.

Longer fermentation -- up to two days in some cases -- doubled the dough's antioxidant levels.

This is probably due to yeasts in the dough having more time to release the antioxidant components.

But there is skepticism about the idea of a healthier pizza.

"I would rather people ate their five portions of fruit and vegetables each day, than ate more pizza," said Jacqui Lowdon of the British Dietetic Association.

"They will be getting a high fat intake, and it may make them more likely to choose extra cheese and salami.

"This isn't teaching people about healthy eating."

The research was funded by the US Government and the US grain industry -- without any input from pizza makers.