If average, healthy people have low levels, it is because they are disregarding dietary advice. These do not give an accurate measure of tissue levels, which are more important. Particularly at low levels, white blood cell readings are necessary. Serum levels also fluctuate hourly with intake. Higher WBC levels tend to correlate with lower plasma values.
Plasma values tend to become lower as metabolic demands decrease, as with age.
And no ethical researcher would go around telling people that they are sick when they are not. Were properly controlled studies to show that smoking depleted Vitamin C, the proper response would be to notify the media that smokers should have this information in a value neutral statement. Humane requirements for Vitamin C and its use in clinical medicine. The relation between energy intake derived from estimated diet records and intake determined to maintain body weight. W Mertz, JC Tsui, JT Judd, S Reiser, J Hallfrisch, ER Morris, PD Steele, E Lashley.