A longitudinal study of how disability has affected survival in Swedish populations across 150 years

Background

Studies from across the world report that disability jeopardizes people's health and increases the risk of premature death. The trend has been demonstrated in present-day populations but there has been little research about whether disability affected survival in historical populations. Our objective was to identify long-term developments in the relationship between disability and survival.

Methods

We focused on all causes of mortality in ages 25-42 among groups with any type of disability in Swedish populations in the 1800s, 1900s and 2000s. We used Cox proportional regression and longitudinal micro-level data, measuring both relative differences (HRs) and absolute differences (excess LYL) in premature mortality, across time by disability status and sex.

Results

Although the overall mortality declined profoundly in Sweden during the centuries studied, the strong association between disability and premature mortality persisted, generating a significant disability-survival gap that has held since the 1800s. The absolute difference in this gap narrowed only slightly during the 1900s, from excess LYL due to disability for men of 1.67 (CI 0.17-3.44) in the 1800s, to 0.69 (CI 0.54-0.85) in the 2000s, while for women the change was even smaller, from 1.24 (CI -0.46-3.12) to 0.59 (CI 0.43-0.69). However, the relative difference widened, particularly for women, from HR of 2.46 (CI 0.91-6.70) in the 1800s to HR 12.00 (CI 9.88-14.60) in the 2000s. For men we found a change in HR from 2.30 (CI 1.31-4.06) to 8.48 (CI 7.26-9.92).

Conclusions

Our study is unique in providing comprehensive results about how disability has limited survival for more than 150 years. In Sweden, fundamental societal changes and extensive welfare provisions promoting equality in health and social wellbeing of all citizens have not been enough to improve the survival of younger generations with disabilities.

Key messages

• The strong association between disability and premature mortality persisted from the 1800s to the 2000s.

• In Sweden, fundamental societal changes and extensive welfare provisions promoting equality in health have not improved survival of young adults with disabilities.

Disability risks in past populations: Sweden from the 1800s until 1959

Background

While diseases in contemporary and past populations are thoroughly studied, the knowledge about disability and the risks of getting it is poor. Like diseases, disabilities increase with growing age affecting primarily elderly groups. Whether this notion holds historically and for other groups at risk for disability and differences over time is not known. This study estimates the disability risks in Swedish populations c. 1800-1959 by age, sex and disability type (sensory, physical, mental).

Methods

We use data on two historical populations in the 1800s (N = 36,500; 550 with disability) and 1900-1959 (N = 194,500; 4,700 with disability) drawn from digitized parish registers reporting socio-economic and demographic characteristics over lifetime and on disabilities. Cox proportional regressions estimate disability risks across time by group (age, sex, disability type).

Results

Our preliminary results based on unadjusted estimates from 1900-1959 suggest that the disability risks doubled or more. In the 1950s, women had 2.6 times higher risk than 50 years before, while it was 2.0 for men. The major rise started in the 1930s (Men 1.51; Women: 1.67), and grew in the 1940s (Men 1.80; Women: 2.14). Next, we will assess these risks by group and in the 1800s.

Conclusions

From 1900-1959, Swedish populations experienced consistently higher disability risks, which doubled for men and almost tripled for women. These risks increased while improvements in public health and economic growth would subsequently make Sweden internationally known as a modern welfare state. That health improvements did not reduce the disability risks but the reverse, was possibly due to higher recognition or labeling of disabilities.

Key messages

Evolution of the selfing syndrome: Anther orientation and herkogamy together determine reproductive assurance in a self-compatible plant

Capacity for autonomous self-fertilization provides reproductive assurance, has evolved repeatedly in the plant kingdom, and typically involves several changes in flower morphology and development (the selfing syndrome). Yet, the relative importance of different traits and trait combinations for efficient selfing and reproductive success in pollinator-poor environments is poorly known. In a series of experiments, we tested the importance of anther-stigma distance and the less studied trait anther orientation for efficiency of selfing in the perennial herb Arabis alpina. Variation in flower morphology among eight self-compatible European populations was correlated with efficiency of self-pollination and with pollen limitation in a common-garden experiment. To examine whether anther-stigma distance and anther orientation are subject to directional and/or correlational selection, and whether this is because these traits affect pollination success, we planted a segregating F2 population at two native field sites. Selection strongly favored a combination of introrse anthers and reduced anther-stigma distance at a site where pollinator activity was low, and supplemental hand-pollination demonstrated that this was largely because of their effect on securing self-pollination. The results suggest that concurrent shifts in more than one trait can be crucial for the evolution of efficient self-pollination and reproductive assurance in pollinator-poor habitats.