nodejs/mongodb - reading out one specific element

I want to read out one specific element out of mongodb

db.collection('profiles', function(err, collection) {
    collection.findOne({'email': mail}, function(err, item) {

this reads the whole entry
for example:

{
  "email" : "asdd@asd.de",
  "password" : "asd",
  "_id" : ObjectId("51c8790f912501e403000001")
}

how can i read out only one of those elements
for example password

{
  "password" : "asd"
}