Yes it has; but the "salt causes high BP, fluid retention etc" is a persistent myth, very indoctriated.
The first my cases asks about when I tell them to supplement with more, real salt.
-what really happens is that their fluid retention goes away, and the BP normalizes.
In Norway it was a study among pregnant women recently (cant find it in english yet) They found out that the women that drank most water during their pregnancies had most morning sickness / nausea.
"probably because the natrium level goes to low" the scientist big doc med said. So can you believe what the conclution was ??? Unfortunately not to take more, real salt when pregnant... (the fetal fluid needs quite a lot of salt, the salinity is almost as high as sea water)
-No; it was "drink maximum half a liter of water a day when pregnant, to avoid nausea"
This is Science today, 2011.