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Cigarette smoking dose-response

Dose-response study
Results
Comment

In Bandolier's infancy it looked at some of the facts about the negative health effects of smoking (Bandolier 7), particularly the strong dose-response for lung cancer. Now we have smoking bans, fewer people smoke, and more of those who do smoke, smoke less.

With the changes of the last decade, it is worth revisiting the issue of dose response, particularly when we have good evidence at the lower end of the dose-response curve [1], and for effects other than lung cancer.

Dose-response study


Inevitably the evidence comes from an observational study. In this case [1] it stems from screening examinations for cardiovascular disease in parts of urban and rural Norway that began in the 1970s. The screening included questionnaires about cardiovascular disease, demographic measures, blood tests and questions about smoking habits.

Excluded were people with a history of chronic disorders like heart disease, diabetes, or hypertension, and ex-smokers or pipe smokers. That left about 19,000 women and 24,000 men for whom death and cause of death could be determined by the end of 2002.

Results


In this sample, 42% of women and 65% of men smoked. Men who smoked mostly smoked 10 cigarettes a day or more, while women rarely smoked more than 15 cigarettes per day. The lowest consumption, 1-4 cigarettes per day, involved 4% of women and 3% of men (Figure 1).


Figure 1: Smoking habits of 23,500 men and 19,000 women in Norway in the mid 1970s






Across the whole population, the average age at the screening event was about 42 years, and BMI about 24. In women who smoked, the duration of smoking averaged 12 years for the lightest smokers (1-4 cigarettes a day) to 20 years in the heaviest (25+ a day). In men who smoked, duration ranged from 18 to 24 years. Average total cholesterol was quite high, over 6.5 mmol/L.

Figures 2 to 5 show the actual number of events per 100,000 person years for men and women, for all cancer, for lung cancer, for ischaemic heart disease, and for all death. There was a strong dose response with cigarette consumption, with more cancers, lung cancers, cases of ischaemic heart disease, and death with more cigarettes smoked. Ischaemic heart disease affected women less than men (Figure 4).


Figure 2: All cancer by cigarette consumption







Figure 3: Lung cancer by cigarette consumption







Figure 4: Ischaemic heart disease by cigarette consumption







Figure 5: All-cause mortality by cigarette consumption







Figure 6: Relative risk for lung cancer according to cigarette consumption






The strongest dose response was for lung cancer (Figures 3 and 6), where smoking 10-15 cigarettes a day increased the risk by 17-fold, and 25 a day or more by about 35-fold compared with not smoking. For all-cause deaths, all cancers, and ischaemic heart disease there was higher relative risk with more cigarettes. Even with 1-4 cigarettes a day there was a significantly increased risk of all cause mortality, ischaemic heart disease, and lung cancer in both men and women. Relative risks were about 1.5 for all cause mortality, 2.8 for ischaemic heart disease, and 3-5 for lung cancer.

Comment


No apologies for a revisit. In the UK parents can still take children into pubs for a meal, into atmospheres with a high proportion of tobacco smoke. Smoking bans in many parts of the world have been successfully implemented, and it is only when you go somewhere without one that one realises just how much of an imposition smoking can be.

Getting down the dose response curve is good if you are at the top. Stopping people being on the curve at all is so much better.

Reference:


  1. K Bjartveit, A Tverdal. Health consequences of smoking 1-4 cigarettes per day. Tobacco Control 2005 14: 315-320.

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