Washington, May 18 (PTI) A skull condition thought to be extinct not only still exists, but is also fairly common in North America and South Africa, a new study has found.

Cribra Orbitalia (CO) is a condition in which the bone inside the eye sockets becomes porous, researchers from North Carolina State University (NC State) in the US and the University of the Witwatersrand in South Africa said.

It is not known to cause any adverse health effects, but is generally regarded as being caused by iron deficiency anemia, they said.

The condition has traditionally been used by anthropologists to assess diet and health in prehistoric populations. For example, the presence of CO could tell researchers that a population was not getting a sufficiently varied diet.

"But there has been a lot of debate about the prevalence of CO in modern populations, with some saying it had effectively disappeared," said Ann Ross from NC State.

"We wanted to know if CO was still extant and, if so, how common it is in modern populations, relative to earlier eras," said Ross.

For the study, researchers looked at modern, historic and prehistoric human remains from South Africa, North Carolina and the Western Hemisphere Database.

They evaluated data on 844 skulls - 245 prehistoric, 381 historic (as recent as the early 20th century) and 218 modern.

Researchers found that CO was not only present in modern populations, but that it was not even uncommon.

For example, they found that two of the five modern North American juvenile skulls - 40 per cent - had CO. And 15 of the 60 South African juveniles ? 25 per cent ? had CO.

"We thought we might see some CO, but not to the extent that we did. The high rates may stem from the fact that these remains were part of forensic cases - there were often related to cases of homicide or neglect," said Ross.

"These cases are not representative of health for all children," she said.

Overall, researchers found that 12.35 per cent of modern North Americans and 16.8 per cent of modern South Africans, across all age groups, had CO.

Both rates are higher than their historic counterparts. Only 2.23 per cent of historic South African skulls evaluated had CO, and only 6.25 per cent of historic North American skulls, researchers said.

Even the prehistoric North American skulls had a lower rate of CO, at 11.86 per cent, they said.

"We think the increased prevalence of CO in the modern skulls may be due to intestinal parasites in some populations and iron-poor diet," said Ross.

"These findings drive home the fact that disadvantaged socioeconomic groups, and parts of the developing world, are still struggling with access to adequate nutrition," she added.

The findings were published in the journal Clinical Anatomy. PTI SAN SAR SAR