Smoking and drinking 15+ units/week was the riskiest behaviour for all the causes of death considered in this study. Men in this category smoked more cigarettes/day than current smokers in the other drinking categories, suggesting that excess drinking and heavy smoking occur together, and the extra number of cigarettes/day may be contributing to the excess mortality. Smoking had stronger effects than alcohol for most of the causes investigated. Current smokers had consistently high mortality rates. Ex-smokers had lower mortality than current smokers, showing the beneficial effects of smoking cessation, but they had higher mortality than never smokers, especially due to respiratory disease and smoking-related cancer. This demonstrates the long-lasting effects of smoking, even after stopping. We have previously shown that consuming 15 units or more per week of alcohol was associated with increased mortality from several causes. We now show that both smoking and drinking 15 or more units/week increased mortality from some of the above causes and also smoking-related cancer. For the specific causes, there was a protective effect of alcohol seen in CHD mortality, particularly for never smokers, but for stroke mortality, both smoking and alcohol were important. Adjusting for a wide range of confounders attenuated the relative rates but the effects of alcohol and smoking still remained. There could also have been residual confounding due to unmeasured variables such as diet. The interaction terms were not found to be significant: this could have been due to lack of power rather than to no effect. The numbers of deaths from stroke, alcohol-related and respiratory causes were small for never smokers, and may have had insufficient power to detect associations in this cohort.
Lower socioeconomic position and low educational attainment were strongly related to both alcohol consumption and smoking in this cohort. For example, 30% of the manual men were both smokers and heavy drinkers compared with only 13% of the non-manual men. On the other hand, only 11% of the manual men were never smokers who drank less than 15 units per week or not at all, compared with 19% of the non-manual men. Given the increased mortality rates associated with both smoking and heavy drinking, this will inevitably contribute to socioeconomic health inequalities. We also recently showed that in this cohort a combination of heavy drinking and obesity had a supra-additive impact on mortality from liver disease, further underlining the consequences of multiple risk factors and their potential effect on health inequalities if they are socially patterned. A study of 16,980 men and women in the Netherlands in 1991-8 showed much lower prevalences of smoking and excessive alcohol consumption but similar socioeconomic differences. Smoking and excessive alcohol consumption ranged from 3.5% in the highest educated men and women to 6.1% in the lowest. In a study of 22,457 middle-aged men and women from Norfolk, United Kingdom in 1993-7, there were more current smokers in lower social classes but the proportion drinking 14 or more units of alcohol per week was greater in higher social classes, unlike the current study. A study of tobacco and hazardous or harmful alcohol use in 39,290 participants from Thailand in 2004 found the strongest predictor of harmful or hazardous alcohol consumption was smoking and the strongest predictor of smoking was harmful or hazardous alcohol use in both men and women. That study found no relationship between both smoking and excess alcohol consumption with education, but suggested that men in middle income groups were more likely to both smoke and use excess alcohol. The message here seems to be that social patterning of drinking and smoking is culturally specific. Other than recognising the adverse consequences of combining both, their social patterning cannot be generalised from one country or even one region to another.
There have been other studies of the effects of smoking and alcohol consumption on mortality, but they did not have such a long follow-up as in the current study, nor were they able to investigate the effects on as many different causes of death.
Our results for all cause mortality were similar to those from a large study of 18,244 middle-aged Chinese men, screened in1986-9, although the follow-up time was only 6.7 years on average and smoking and alcohol definitions were different. Within each drinking category, risk of death was higher for smokers and increased with amount smoked. Within each smoking category, there was a suggestion that drinkers of 1-28 drinks/week had a lower risk of death than non-drinkers or heavy drinkers. The highest risk was seen in the heaviest drinkers who also smoked. A 1986 study of 30,518 women aged 55-69 in the United States, with 14 years of follow-up analysed the relationship between alcohol and mortality and cancer incidence by each smoking category separately. Alcohol consumption was inversely associated with all cause and CHD mortality for never and ex-smokers, and was positively associated with cancer incidence for current and ex-smokers. There were no clear associations with cancer mortality. Attention was drawn to the lack of a protective effect of alcohol on CHD mortality in smokers: this was also observed in the current study. A study of 64,515 Chinese men aged from 30 to 89 screened between 1996 and 2000, with an average of 4.6 years of follow-up related alcohol and smoking to mortality in a similar way to the current study. The highest all cause mortality was seen in the heavy drinkers and heavy smokers. There was a protective effect of moderate drinking for all cause and cardiovascular disease (CVD) mortality which was stronger in non-smokers than ever smokers. Heavy drinking was associated with increased cancer mortality and there was no protective effect seen in moderate drinking for cancer mortality, even in the non-smokers.
Other studies have looked at incidence of disease rather than mortality. In a study of stroke incidence in 1991-2 of 45,449 Swedish women aged 30-50, with an average of 11 years of follow-up, current smokers who did not drink alcohol had a four-fold increased risk of stroke compared with never smokers who did not drink. Current smokers who did drink alcohol had lower relative risks than current smokers who did not drink alcohol; however, the numbers of women and cases of stroke were low in the higher alcohol category (≥ 70 g/week) in that study (3,793 women with 17 stroke cases), raising the possibility that an adverse effect of heavy drinking could have been missed. There was some evidence of a protective effect of moderate drinking in never smokers. No such protective effect of alcohol was seen with stroke mortality in the current study, but this could be because they were older, were men and stroke mortality rather than incidence was being investigated. A pooled analysis found positive relationships between alcohol and lung cancer among non-smoking men only although the absolute risk of lung cancer was small in that group. There were no relationships seen for smokers, former smokers or non-smoking women. In a large study of women in 1996-2001, increasing alcohol intake was strongly associated with the incidence of upper aerodigestive tract cancers in current smokers, but not in never or former smokers.
The current study showed that alcohol and smoking both contribute to mortality risk. However this may not necessarily be the case for all causes. A large study of UK women in 1996-2001 showed that alcohol consumption reduced, but smoking increased the risk of gallbladder disease death or hospital admission. That study also showed large effects of both smoking and alcohol on death or hospital admission for cirrhosis.
The strengths of the study were the long follow-up, which was almost complete, and the ability to adjust for several risk factors and look at several causes of death. For example, unlike in other studies, CVD was broken down into CHD and stroke. This is important as alcohol consumption can have very different effects on these two diseases. We were also able to keep ex-smokers as a separate group, whereas other studies combined ex and current smokers to form an ever smoking group.
In common with other longitudinal studies, alcohol consumption was self-reported and may thus have been underestimated. We have previously reported on the reliability of the alcohol data from the present cohort. Former drinkers were classified as non-drinkers, as we could not differentiate between former drinkers and never drinkers. Former drinkers may be unhealthier than the other non-drinkers if they had given up due to poor health, which could increase the mortality risk in the non-drinkers. However, this cohort of working men would be expected to be healthier than other cohorts so we would expect fewer former drinkers among the non-drinkers. As alcohol and smoking were reported at screening, we do not know if these practices were continued or changed during follow-up. If some ex-smokers took up smoking again, it would have the effect of increasing mortality in the ex-smokers. Also some current smokers at screening would have subsequently given up, which would decrease the mortality in the current smokers. Our main analyses did not take into account the amount of cigarettes smoked in the current smoking group. However there was little effect of additionally adjusting for all the associated smoking habit variables. Although adjustment was made for several covariates, the study did not record others such as dietary intake, family history of disease or adequate information on exercise. The cohort consisted of employed men, who would be healthier on average than men from general populations, so the results may underestimate absolute risk, but the relative risks are likely to be generalisable to male populations from similar contexts.
Smokers who also drank 15+ units/week had the highest risk of dying from all the causes compared to the other groups. Drinking 15+ units is lower than the weekly upper limit of 21 units recommended by the UK government for men. As it has been shown previously in this cohort that drinking 15-21 units per week and over leads to an increased risk of mortality, the cut-off of 15 was a reasonable choice, although we do not have sufficient data on consumption throughout the follow-up period to recommend changing the weekly limits. Smoking had a greater adverse effect on mortality than alcohol consumption, and ex-smokers who had stopped smoking before the screening examination had lower mortality risks than smokers. These findings reinforce the importance of continuing to prioritise smoking cessation across the whole population. Given the strong links between smoking and heavy drinking, it may also be helpful to devise policies aimed at reducing both smoking and alcohol consumption in population groups where this is common.