The Romans, as Monty Python famously acknowledged, have done many things for us. Contrary to popular wisdom, however, improving our diet was not one of them.

A study of the remains of almost 20,000 people dating from the 8th century BC to the 18th century AD has found that the Roman empire reduced our level of nutrition, which increased again in the "dark ages".

That is because the key factor in determining average height over the centuries – an indicator of nutritional status and wellbeing – has been an increase in milk consumption due to improved farming. Higher population densities and the need to feed the army during Roman times may have worked against this.

The "anthropometric" approach pursued by Nikola Koepke of Oxford University, which combines biology and archaeology, suggests longer bone length is indicative of improved diet. Koepke's study, presented at the Economic History Society's 2010 annual conference, also challenges assumptions about the effect of the industrial revolution. Urbanisation did not improve wellbeing, she argues, at least as measured by height.

Rather, Koepke says, the key factor in determining average height growth over the past 2,500 years has been the increased consumption of milk as a result of the spread of, and improvements in, farming. She found that overall European living conditions improved slightly in the past 2,500 years even in the centuries prior to the industrial revolution.

Her study is based on data compiled from analysing the skeletal remains of more than 18,500 individuals of both genders from all social classes, from 484 European archaeological dig sites. "Higher milk consumption as indicated by cattle share had a positive impact on mean height," Koepke writes. "Correspondingly, this determinant is the key factor in causing significant European regional differences in mean height."