Italian and British researchers investigating a prehistoric cemetery in central Sudan have found what they believe are the oldest prostate stones, revealing the disease affected men as early as 12,000 years ago.

The stones, as large as walnuts, were found in 2013 in the pelvic area of an adult male in a burial discovered in the prehistoric cemetery of Al Khiday. The cemetery lies on the left bank of the White Nile some 12 miles south of Omdurman (Khartoum).

The remains of the man, who likely experienced extreme pain in the course of the disease, were unearthed as a team led by Donatella Usai and Sandro Salvatori, at the Center for Sudanese and sub-Saharan studies in Treviso, Italy, investigated some 900 square miles in the prehistoric cemetery.

Usai and colleagues, who detailed their findings in the journal PLOS ONE, recovered 190 graves. The burials date to three different periods, from as early as 12,000 years ago to 2,000 years ago.

The oldest graves, dated as pre-Mesolithic, included 94 individuals, including the male affected by prostate stones.

Intriguingly, the man was buried facedown, as the majority of the pre-Mesolithic burials.

"The high frequency of prone burials rules out they are deviant burials. It rather suggests a funerary rite with a yet mysterious symbolic meaning," Donatella Usai told Seeker.

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The position in which the stones were found - one between the pelvic bones and two close to the lumbar vertebrae - immediately suggested the individual may have suffered from urinary bladder stones. The stones develop in the prostate, a gland of the male reproductive system located in the pelvic space.

At first researchers thought the stones might actually be just that - stones. But testing proved they had been formed in the man's prostate.

"The mineralogical composition, the heterogeneous and concentric microstructure of the stones and their density, much lower than that found in rocks, absolutely confirm a biogenic origin," Lara Maritan, at Padova University's Department of Geosciences, told Seeker.

To rule out the ovoid objects were kidney stones or gallstones, the researchers carried out a range of analyses.

"Pathological stones have differential mineralogical compositions," Usai and colleagues wrote.