We thank Dr Graham F Cope for his valuable remarks, and agree that underreporting of daily cigarette consumption might be of importance when assessing the risk in light smokers.1
Dr Cope refers to two papers: a cross sectional randomised study on smoking reduction in pregnant women, and an assessment of smoking status in patients with peripheral arterial disease.2,3 Our study did not concentrate on subgroups in need of regular medical attention; it covered all residents aged 35–49 years, except people with a history or symptoms indicating cardiovascular diseases (among them peripheral arterial disease) and diabetes.4 A general population in the 1970s may be less inclined to underreport consumption, than present day pregnant women and sick people, who do not want to incur the disapproval of the healthcare professionals.
Based on a review and meta‐analysis, Patrick and co‐workers found that interviewer administered questionnaires, observational studies, reports by adults, and biochemical validation with cotinine plasma were associated with higher estimates of sensitivity and specificity.5 Our study compares favourably with these points: the study includes only adults, all questionnaires were checked by a nurse in an interviewer situation, and in one of the three counties, biochemical validation was carried out in all participants by determination of serum thiocyanate.6 Certainly, levels of thiocyanate may be influenced by factors other than smoking; nevertheless, the dose–response between mean levels of thiocyanate and reported number of cigarettes is remarkable (table 1).
Table 1 Dose–response between mean levels (μmol/l) of thiocyanate and reported number of cigarettes.
| Number of cigarettes per day | Males | Females | ||
|---|---|---|---|---|
| No. | Mean (SD) | No. | Mean (SD) | |
| 0 | 6212 | 33.9 (14.0) | 7908 | 33.5 (14.2) |
| 1–4 | 169 | 45.3 (18.4) | 515 | 52.0 (22.0) |
| 5–9 | 855 | 59.6 (20.7) | 1661 | 70.9 (24.5) |
| 10–14 | 1570 | 69.6 (22.2) | 1800 | 81.5 (24.0) |
| 15–19 | 1056 | 76.3 (23.1) | 569 | 90.8 (25.5) |
| 20–24 | 699 | 81.5 (26.4) | 247 | 96.1 ((25,6) |
| 25+ | 235 | 87.3 (27.9) | 36 | 99.7 (28.3) |
Finally, the attending persons reported their actual number of cigarettes per day in a special box in the questionnaire. Here they were allowed to give a range of daily consumption—for example, 10–15 cigarettes. In our analyses, however, we used the highest figure stated by the participant. Hence, a report of 3–6 cigarettes per day was categorised in the 5–9 cigarettes group.
We find it reasonable to conclude that the results presented in our paper reflect a marked increased risk in light smokers.
References
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