Trends in vascular and non-vascular mortality rates in UK population
The figure shows the age standardised annual UK mortality rates for vascular and non-vascular causes of death at ages 35-69 between 1950 and 2005. Throughout this period, vascular mortality rates in middle age in men were about twice those in women, peaking in 1970 and declining linearly by about 2% a year in both sexes (or by almost 70% between 1970 and 2005). The proportion of deaths attributed to vascular disease in middle age also declined between 1970 and 2005, from about 50% to 30% in men and from 40% to 20% in women. The figure also shows age standardised mortality rates from vascular and non-vascular causes for men and women aged 70-79. For both sexes, the absolute mortality rates in old age were about fivefold greater than those in middle age. In old age, vascular mortality rates declined by about two thirds between 1950 and 2005 in both men and women, but non-vascular mortality rates declined to a much lesser extent in this age group. The proportion of deaths attributed to vascular disease in old age declined from about 60% in 1950 to less than 40% in 2005 for both men and women.
Trends in age standardised vascular and non-vascular mortality (mean of annual rates in component five year age groups) by age and sex for 1950-2005 for UK population (source: WHO and UN population estimates)
Trends in cause specific mortality rates in the Whitehall study
Table 1 shows the age specific death rates and number of deaths from specific causes for men in each decade of age at risk. About a quarter of all deaths occurred before the age of 70. The median age at death was 76, and the median time to death 22 years. The proportion of deaths from vascular causes declined with age, ranging from 54% among those in their 50s to 45% among those aged ≥80. The overall mortality rate increased threefold for every 10 year increase in age (hazard ratio per 10 years older 2.95, 95% confidence interval 2.87 to 3.07), but mortality rates for stroke and respiratory disease increased over fourfold for every 10 year increase in age.
Table 1 Cause specific mortality* by age (years) at death. Figures are rates (number of deaths)
Table 2 shows the distribution of deaths by calendar period over the 38 year follow-up and the age adjusted hazard ratios for specific causes of death per 10 year increase in calendar period. The secular reductions in vascular and non-vascular mortality rates observed in the Whitehall study were similar to those observed for the UK population as a whole (figure). After adjustment for age at risk, the decline in vascular mortality rates was more than twice that for non-vascular causes (hazard ratio per 10 year calendar period: 0.75 (0.73 to 0.79) for vascular causes and 0.89 (0.86 to 0.93) for non-vascular causes). The age adjusted mortality rates for cancers probably related to smoking declined by about 23% per 10 years, whereas those believed to be unrelated to smoking were unaltered (0.77 (0.72 to 0.82) v 1.03 (0.96 to1.11), respectively), illustrating the importance of cessation of smoking in this population.
Table 2 Cause specific mortality by calendar period of follow-up. Figures are deaths; hazard ratios adjusted for age at risk (95% confidence intervals)
Comparison between levels of risk factors recorded in middle and old age
Among the 7044 men who completed the questionnaire in 1997, 13% were current smokers (compared with 40% of all men in 1967-70) and 58% were ex-smokers. Of the ex-smokers, the mean age at quitting smoking was 52, an average of 26 years earlier (that is, shortly after entry into the study). In addition, of the men who had been cigarette smokers in 1967-70, just 29% were still current smokers at re-survey (indicating that over two thirds had quit, for some reason, during that time). Mean blood pressure, cholesterol concentration, and BMI were obtained for 4811 men at re-survey, of whom 1930 had no history of disease or medication to lower blood pressure or cholesterol concentration. The difference between mean levels of systolic blood pressure for men with “high” versus “low” blood pressure at baseline declined by over two thirds (30.6 v 8.3 mm Hg) between 1967-70 and 1997 in all men with available data (see table A on bmj.com). Similarly, the difference in mean levels between “high” and “low” cholesterol declined by over two thirds (1.86 v 0.49 mmol/l) over this period in all men (see table A on bmj.com). Differences in BMI between the obese and non-obese groups, however, declined to a lesser extent (9.9 v 5.6) over this period. Exclusion of men with previous disease or use of medication to lower blood pressure or cholesterol concentration did not materially alter the extent of the observed variability within individuals.
Cardiovascular risk factors and life expectancy
Table 3 shows the prevalence of the major cardiovascular risk factors at entry and their relation with vascular and non-vascular mortality and life expectancy. In 1967-70, 7919 men (42%) reported that they were current cigarette smokers and 3502 (18%) reported that they had never smoked tobacco. After adjustment for age and calendar period, the hazard ratios associated with current smoking compared with never smoking were 1.57 (1.46 to 1.69) for vascular mortality and 2.07 (1.92 to 2.22) for non-vascular mortality. Current smoking defined at study entry was associated with an average 6.3 year difference in life expectancy at age 50 compared with non-smoking. As the re-survey of survivors in 1997 indicated that about two thirds of smokers quit smoking within a few years after entry into the study, the observed effects of current smoking for cause specific mortality have probably been underestimated by about 50% (see appendix on bmj.com).
Table 3 Hazard ratios for vascular and non-vascular mortality and life expectancy by risk factors at study entry when examined separately
Table 3 shows that the difference in life expectancy between the highest and lowest fifths of systolic blood pressure was 5.2 years. Even dichotomising blood pressure crudely into two categories, “high” versus “low” blood pressure (corresponding to a “usual” difference in systolic blood pressure of probably about 15 mm Hg (see table A on bmj.com) was associated with a hazard ratio of 1.64 (1.56 to 72) for vascular mortality, and 1.09 (1.04 to1.14) for non-vascular mortality and a 3.5 year shorter life expectancy (see table B on bmj.com). “High” cholesterol (corresponding to a “usual” difference in total cholesterol of probably about 0.9 mmol/l; see table A on bmj.com) was associated with a hazard ratio of 1.24 (1.18 to1.30) for vascular mortality, and a one year shorter life expectancy at age 50 (see table B on bmj.com). Table 3 shows that difference in life expectancy between the highest and lowest fifths of total cholesterol concentration was 1.9 years. Differences in upper and lower employment grades were associated with 5.4 year difference in life expectancy. Married men had a 2.2 year longer life expectancy than unmarried men (but this association was entirely explained by differences in the other risk factors). Glucose intolerance or diabetes mellitus at baseline (prevalence 6.9%) was associated with a 3.6 year shorter life expectancy at age 50.
Associations of life expectancy with combinations of cardiovascular risk factors
Table 4 shows the effects of combinations of the three main risk factors for cause specific mortality and life expectancy. The hazard ratios for vascular mortality increased progressively with increasing number of cardiovascular risk factors when compared with men without any of them. Compared with the 17% of men without any baseline risk factors, men with all three risk factors (8.3%) in 1967-70 had a threefold higher vascular mortality rate, a twofold higher non-vascular mortality rate, and a 9.6 year shorter life expectancy from age 50 (23.7 v 33.3 years).
Table 4 Hazard ratios for vascular and non-vascular mortality and life expectancy by cardiovascular risk factors at entry when examined in combination
Associations of life expectancy with mortality risk scores
Classification of men by fifths of a risk score based on four categories of smoking and continuous measures of blood pressure and cholesterol concentration was associated with a 9.3 year difference in life expectancy at age 50 (24.2 v 33.5 years) between the highest and lowest fifths (table 5). Additional inclusion of glucose intolerance, employment grade, and BMI was associated with a 10.4 year difference in life expectancy at age 50 (23.6 v 34.0 years) between the highest and lowest fifths, and a 15.2 year difference (20.2 v 35.4 years) when the highest and lowest 5% of the distributions were compared (table 5).
Table 5 Hazard ratios for vascular and non-vascular mortality and life expectancy by all cause mortality risk scores