Smoking habits of black South African patients with diabetes mellitus.

Cigarette smoking is a major arteriosclerotic risk factor, and this is enhanced by the presence of diabetes mellitus. Although smoking rates are increasing in many African countries, they have been little studied. We have critically assessed smoking among black diabetic and general medical patients at Baragwanath Hospital in Soweto, South Africa. As well as direct questioning of patients, we also used urinary cotinine:creatinine ratio as an objective marker. The admitted smoking rate was 16% in 118 diabetic patients, compared with 22% in 105 medical patients. Using a validated biochemical index of smoking (urinary cotinine:creatinine > 1.0 microgram mg-1) the rates were 37% and 33%, respectively. Most of the excess however was due to women who took snuff, and when excluded, the estimated real rates were 20% (diabetic) and 24% (medical). Amongst diabetic smokers mean cotinine:creatinine ratio was higher than in medical smokers (4.7 +/- 6.0 v 1.8 +/- 2.0 micrograms mg-1) despite admitted similar smoking consumption. A separate control group of British smokers had a mean level of 3.6 +/- 1.3 though their consumption was twice that of the South African groups. We conclude that smoking is common among South African black diabetic patients (20%), though it is less than reported figures for the black general population (28%), and British diabetic patients (35%). Questionnaire studies may seriously underestimate smoking rates, though this effect is considerably less in African compared with British smokers. Urinary cotinine also allows quantification of the 'smoking load', which is rarely reflected by admitted cigarette consumption.