is smoking one cigarette a day harmful 'increases heart disease and stroke risk' One cigarette a day is

The prevalence, predictors and associated health outcomes of high nicotine dependence using three measures among US smokers

So there seems to be a nexus there, Levy said

4 There are a number of brands and products on the market that convert nicotine to a vapor that can be easily inhaled, and they are generally labelled according to their nicotine content as extra strong/very high, strong/high, regular/medium, light/low, ultra-light/very low and zero/no nicotine. 4 However, traces of nicotine have been found in e-cigarette cartridges labelled no nicotine, which indicates that the information on packaging about nicotine levels may be purposely misleading

none of the above

They might even make it all the way to the ocean