Unlike most Matlab plotting functions, heatmap is annoyingly heavy-handed. It really wants to be used as a quick browsing tool, with very little customization allowed.
You can extract the color data from it:
tbl = table(LastName,Age,Gender,SelfAssessedHealthStatus,...
h = heatmap(tbl,'Smoker','SelfAssessedHealthStatus');
Alternatively, you may want to look some histogram functions (e.g. histcounts2) to calculate heatmap-like values without the plotting overhead.