Achieving a 25% reduction in premature non-communicable disease mortality: the Swedish population as a cohort study

Although Sweden achieved a 25% reduction in premature NCD mortality during the period 1991 to 2006, this was not done against any specific international target, but simply as part of continuing improvements in public health in Sweden, and against a background of relatively good socio-economic conditions and biomedical advances. Nevertheless, it clearly demonstrates that this rate of reduction in premature NCD mortality in countries at relatively late stages of epidemiological transition is possible.

The unique level of detail and completeness in the Swedish population registers provides an unparalleled opportunity to examine how the 25% reduction in premature NCD mortality came about. Figure 2 shows that there were bigger relative reductions in premature NCD mortality over time for the younger age groups. Mortality rate differences between various sub-groups were very predictable; being partnered, more educated, and employed in higher income groups were all protective against premature NCD death, even though each group underwent its own mortality transition over time. Being male carried a higher risk than most background factors for premature NCD death. These mortality inequalities are generally consistent with those reported from a large-scale European study [9].

The ‘not employed’ and ‘Swedish-born’ categories within the analysis need special interpretation. Those ‘not employed’ included ‘retired’ people (mostly in the 60 to 69 year age group) as well as those who were unemployed for other reasons such as sickness. Consequently, there were relatively high mortality rate ratios associated with not being employed, even after adjustment for age. The in-migrant group experienced a considerable mortality advantage compared with those born in Sweden in earlier periods, but this reduced to a nil difference in the final time period. This may be consistent with a ‘healthy migrant’ effect (whereby self-selection means that migrants might be less likely to have NCDs on arrival), but this difference seemed to diminish over time [10].

Causes of NCDs are multi-factorial, and associated with social determinants of health, including physical, environmental, biological, behavioural, and socio-economic factors. Latency periods between NCD risk exposures and mortality outcomes are also complex. In Sweden, the current prevalence of daily smoking among men is lower than among women and also low compared with other European countries [11]. As smoking has declined significantly in recent decades, alcohol consumption has increased [12]. The proportion of overweight and obese people has also increased, particularly among lower educated groups [13]. Past risk exposures will have driven our mortality findings during the 1991 to 2006 period, and, combined with more recent exposures, will contribute to determining future NCD mortality in Sweden.

We were unable to consider NCD risk factors such as obesity, smoking, alcohol consumption, and physical activity on an individual basis in the Swedish dataset, and hence are unable to conclude on the potential contributions of NCD risk-reduction strategies to the premature NCD mortality reductions observed. Further work is being conducted to examine how major NCD risk factors may have influenced premature NCD mortality reductions in an area of northern Sweden, in a population for which detailed individual risk factor data are available. Modelled findings have suggested that reducing NCD risks can contribute considerably to mortality reductions in the context of the 25 × 25 target [14]. Risk reduction is also, therefore, likely to be an important component of national strategies aimed at the target.

In real terms for the Swedish population, the reductions in premature NCD mortality achieved from 1991 to 2006 corresponded to about 3,000 premature deaths averted annually. The 25% target reduction was achieved against the background of continuing population ageing in Sweden, though younger age groups benefited to a greater extent from mortality reductions. This suggests that the WHO 25 × 25 target is robustly formulated in considering the unconditional probability of dying, rather than taking any other more complex endpoint. However, having achieved a 25% reduction in a previous generation does not necessarily mean that Sweden can achieve it again for the 2010 to 2025 period, as defined in the WHO 25 × 25 target. It was clear from our analyses that most of the deaths averted in Sweden were associated with reductions in premature cardiovascular mortality, whilst the other major component of premature NCD deaths, cancer mortality, reduced by a much smaller proportion. Furthermore, the overall rate of reduction in premature NCD mortality fell steadily during 1991 to 2006, which does not augur well for what might be achievable in Sweden during 2010 to 2025.

There is therefore a distinct possibility that Sweden, along with other countries already at a late stage of epidemiological transition in 2010, will not go on to achieve the 25 × 25 target, partly because of their earlier successes. In purely demographic terms, there is a potentially perverse effect whereby initial mortality reductions across the 30 to 69 age group may lead to increasingly equal numbers of people in each year of age, hence increasing the proportion of older people within the 30 to 69 age group and so making further mortality reductions less possible. In public health terms, depending what strategies are used to facilitate premature NCD mortality reduction, there may also be diminishing returns over time, after higher-risk individual deaths are initially averted.

Thus, although the WHO 25 × 25 target was aimed at all countries irrespective of their stage of epidemiological transition, it is likely that the outcomes in 2025 will not be independent of countries’ 2010 transitional status. It was also clear from the Swedish case that premature NCD mortality accounted for around three-quarters of all mortality in the 30 to 69 year age group, and so any effective overall mortality reduction in that age group has to be predicated on reducing the NCD component. This is likely to be the case for all countries where external and infectious causes of death have already been relatively well controlled in the 30 to 69 year age group. We suggest that NCD management interventions targeted at the upper range of the premature age group might be the most effective way for countries to reach the 25 × 25 target, although there may be more long-term benefits from NCD risk factor interventions among younger adults.

Unsurprisingly, the overwhelming burden of premature NCD mortality in Sweden occurred among older men, and this is highly likely to follow similar patterns elsewhere. Data from the INDEPTH Network suggested that, for Africa and Asia, where most deaths are not routinely documented, a little under half of adult NCD deaths occurred under 65 years of age, with population-based rates in that age group being broadly similar across Africa and Asia, as well as similar to the rates in Sweden described herein [15]. Since the majority of the world’s population lives in low- and middle-income countries, which are generally at various earlier stages of epidemiological transition than Sweden, it will be important to achieve better measurement and understanding of NCD mortality patterns in such locations in assessing progress towards the 25 × 25 target. Premature NCD mortality in different settings may account for variable proportions of overall mortality, depending on patterns of non-NCD mortality and age-sex population profiles, but there appears to be greater consistency than might be supposed in population-based rates of premature NCD mortality. In Sweden, higher levels of education and income were generally protective factors, and men carried a higher mortality burden, so countries aiming at the 25 × 25 target may well want to develop strategies that target lower socio-economic groups of middle-aged men. The apparently high premature NCD mortality associated with not being employed in Sweden is probably inevitable, and most societies will include sub-groups disadvantaged by life-long medical conditions and other factors that apparently lead to a higher mortality risk. The pattern of mortality in Sweden among in-migrants is interesting in that there was no suggestion from our findings that migrants constituted a group needing special attention in terms of premature NCD mortality risk reduction strategies. This may also hold true elsewhere, because of similar healthy migrant effects.

A global consideration of premature mortality burdens, though necessarily dependent on much scantier data than those available for Sweden, concluded that there were substantial reductions in mortality over the period 1970 to 2010 and was reasonably optimistic about the prospects for further global reductions [16]. This review, however, noted that countries would need to set different priorities depending on existing mortality patterns in order to achieve maximum benefits.