Queens of the Joseon era (1392-1910) had an average life span of 51 years and were outlived by royal concubines by an average six years, a new study has found.

According to Lee Mi-seon, a researcher at the Academy of Korean Studies, queens lived longer than kings, whose average life span has been estimated to be 47 by other scholars.

Compared to women from the noble class of that era, who lived to 45 on average, the queens also had a considerably longer life.

But they were outlived by the king’s concubines by six years, Lee said.

“It could be that (queens) as the head of all court ladies may have lived under great psychological pressure and stress, resulting in a shorter life span (than that of concubines.)”

The scholar has analyzed data on 46 queens and some 48 of the era’s total 175 concubines whose age at death is known.

The study also looks into the cause of death of 97 queens and concubines.

The No. 1 cause of death was “illness,” as stated in historical documents, accounting for the death of 17. Forced death or execution follows at 16, while 11 died in, during or after childbirth.

Lee’s paper has been published in the latest issue of the Journal of Korean History.