The response rate to the health survey was 85.4% (n = 10 073). Fourteen women whose survey information was not corroborated by the Oral Contraception Study dataset were excluded. Mean age of the responders was 56.1 years (SD = 6.5 years). Over two-thirds were of manual social class, less than 5% were nulliparous, and just over half had a history of serious illness (). Over 20% had smoked for more than 20 pack-years. Less than 4% reported drinking more than 14 units of alcohol weekly, and 8% were ‘never drinkers’, although one-fifth of responders had missing information about alcohol. One-third of ‘never drinkers’ had previously drunk alcohol. Although over half of responders had a BMI outside normal range, less than 1% were underweight. The threshold between the lowest and middle tertile of physical activity was 15 hours per week.
Lifestyle and sociodemographic characteristics associated with mortality among 10 059 responders to the health survey of the Oral Contraception Study.
By December 2006, 896 (8.9%) responders had died, mainly from cancer (n = 389) or cardiovascular disease (n = 267). Median duration of follow-up was 141.7 months (interquartile range = 137.6 to 142.4 months). Following adjustment for potential confounding, compared with ‘never smokers’, those with ≥11 pack-years of smoking had a statistically significant increased mortality risk, with the largest risk in women who had smoked more than 20 pack-years (adjusted hazard ratio [HR] = 2.34, 95% confidence interval [CI] = 2.00 to 2.74, ).
In comparison to women whose weekly alcohol consumption was less than 7 units, ‘never drinkers’ were more likely to die (adjusted HR = 1.66, 95% CI = 1.34 to 2.05). The increased mortality risk associated with more than 14 units of alcohol did not remain statistically significant after adjustment.
Although compared to women with a normal BMI, underweight women were nearly twice as likely to die (adjusted HR = 1.66, 95% CI = 1.03 to 2.68); obese women were not at significantly higher risk of death. Women in the most physically inactive group had a significantly higher mortality risk (adjusted HR = 1.73, 95% CI = 1.46 to 2.04) than those who were most active.
Risk of mortality associated with different combination of lifestyle risk factors. Hazard ratios adjusted for age, social class, parity, and history of serious illness. BMI (outside range of normal body mass index).
Three-quarters of responders (n = 7603, 75.6%) completed all of the lifestyle questions. Most of these women reported more than one lifestyle risk factor (5037/7603: 66.2%), although few (5.8%) had all four (). Among women who reported one risk factor, being physically inactive was the most common, followed by having a BMI outside normal range. More than 13% of the women reported the most frequent risk factor combination: a BMI outside normal range and being physically inactive. Less than 3% had the least frequent combination of: any pack-years of smoking, never drank alcohol or drank ≥7 units weekly, and were underweight, overweight, or obese. At the end of follow-up, 2.0% of the women with none of the risk factors, and 14.4% of those with all four risk factors, had died.
Proportion of women with different combinations (and proportion with combination who died) of modifiable lifestyle risk factors.a
Most risk factor combinations were associated with a statistically significant increased mortality risk when compared with women without any of the risk factors (). Among women with one lifestyle risk factor, the highest mortality estimates were associated with smoking. Although the confidence intervals for the risk estimates were wide and overlapping, the general pattern suggested that women with multiple risk factors had a higher mortality risk than those with one risk factor.
Smoking and physical inactivity had the highest population attributable risks when examined alone or in combination with other risk factors (). If smoking, physical inactivity, BMI outside normal range, and excess alcohol consumption or never drinking had all been removed from the cohort, 59% (95% CI = 31% to 78%) of the deaths could have been avoided. The four lifestyle risk factors, together with age, social class, parity, and a history of serious illness gave a population attributable risk of 91% (95% CI = 59% to 98%).
Population attributable risks (PAR) (95% CIs) of lifestyle risk factors associated with mortality during follow-up.