It’s never really stated it right out, but isn’t the Oath Rod one of the Rods of Dominion that Ishamael talks about to Lews Therin in the prologue of The Eye of the World? Ishamael said, "Once you wore the ring of the Tamyrlin, and sat in the High Seat. Once you summoned the Nine Rods of Dominion." I don’t know, but it seemed to me that those nine rods were very likely the oath rods. But I must agree that the Oath Rod might shorten the Aes Sedai’s lives. If you will remember, at some point in time, one of the female Forsaken (I think it was Semirhage) talks about how she enjoys giving people pain, and that she was a great Healer in the Age of Legends. Then she goes on to say that when she was a Healer, the others found out about her other activities, and that she could either be stilled or be bound to the Hall of the Servants or something like that. It could very likely be, that being bound to the Hall was swearing an oath on the Oath Rod. And if you have someone swear an oath to you on the Oath Rod, you have dominion over them.
wotmania says: The Oath Rod is certainly one of the Nine Rods of Dominion. And it is almost certainly shortening the lives of Aes Sedai - being bound with one of these rods during the Age of Legends was a punishment. And the Kin, who are not using their Oath Rod, live a great deal longer than any current Aes Sedai.
Nine Rods of Dominion