A natural blanket works by conserving the body heat emmitted, and artificially warming up the body in the process, so you could ask is a natural blanket healthy too as it does much the same thing (except the heat source is different). Then ask the same question of clothing. I would opinionate that the only reason they may be unhealthy is that they suppress the body's ability to regulate itself through shivering and sweating, so we are less used to heat changes, when away from the electric blanket. There is another school of thought that there is an (very small) emf induced by a leccie blanket but i think this has been disproved as being detrimental.......