My health improvements from vaping and not smoking. IMO, nicotine has never been the issue with causing health concerns. The burning process and chemicals produced has been.
FDA allows OTC nicotine products
http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm345087.htm
FDA consumer guide allows for multiple use nicotine :"There are no significant safety concerns associated with using more than one OTC NRT at the same time, or using an OTC NRT at the same time as another nicotine-containing product—including a cigarette."