People who have more children may have a shorter life span than those with few kids and the risks are particularly high for mothers, says a new study.

Researchers led by Dustin Penn and Ken Smith of University of Utah looked at case studies of 21,000 couples living in Utah between 1860 and 1985, who bore a total of 174,000 children.

They found that the couples had an average of eight children each, but family size ranged from one to 14 or more children.

The data showed that the more children a couple produced, the higher their risk of early death, reported the online edition of BBC News.

The situation was worse for women because they were directly affected by the physical costs of bearing the kids, it said.

Fathers' mortality risk increased the more children they had, but never exceeded that of mothers. The team looked at deaths after the last child was born and found mothers were also more likely to die after the birth of the last child.

They found that 1,414 women had died within a year of the last child's birth, and another 988 by the time the child was five. In comparison, 613 men died in the first year after their last child was born, with another 1,083 dying within five years.

"Having a large number of children is bad for parents' health, particularly that of mothers," the study stated.