Sustainable working life before and after ischemic heart disease – a prospective cohort study of Swedish twins

Every year, millions of people around the world face a diagnosis of ischemic heart disease, a condition where blood flow to the heart is restricted. While doctors have long understood how this illness affects the body, a different kind of question has remained harder to answer: how does it affect a person's ability to keep working? For many, a job is not just a source of income but a central part of daily life and identity. When a serious health event occurs, the path back to the workforce is often blocked by long periods of sick leave, unemployment, or the need to retire early due to disability. Researchers have known for some time that heart disease increases the risk of leaving the labor market, but they have struggled to separate the direct effects of the disease from other hidden factors. These hidden factors include a person's genetic makeup and the environment they grew up in, both of which can influence both heart health and career longevity. Understanding whether the disease itself is the primary cause of job loss, or if shared family traits play a larger role, is essential for creating better support systems for workers.

To untangle this complex web, a team of researchers in Sweden turned to a unique natural experiment: twins. By studying pairs of twins, scientists can compare individuals who share the same early life environment and, in the case of identical twins, the exact same genetic code. This allows them to see if differences in outcomes are truly caused by a specific event, like a heart attack, or if they are simply the result of shared family history. The researchers focused on a large group of Swedish twins aged between 20 and 60, tracking nearly 6,000 individuals over a period of several years. They identified those who were diagnosed with ischemic heart disease and matched them with twins or other individuals who did not have the disease, ensuring the groups were similar in age, education, and marital status. The goal was to measure "sustainable working life," a concept defined simply as staying employed without long-term sick leave, unemployment, or disability benefits. The team looked at the years leading up to the diagnosis and the years following it to see how the trajectory of a career changed.

The study revealed a clear pattern in how heart disease impacts a working life. Before the diagnosis, both those who would eventually develop heart disease and those who would not showed a relatively stable ability to remain in the workforce. However, once the diagnosis was made, the picture changed for everyone, but more sharply for the patients. Three years after the cohort entry year, the probability of maintaining a sustainable working life began to decline for the entire group. Those with the heart disease experienced a slightly steeper drop than those without it, indicating that the illness does indeed make it harder to stay employed. This decline was observed, and no significant differences were found in these trends based on whether the person was male or female, or whether they had a history of common mental health conditions like depression or anxiety. The data suggested that the presence of the heart disease itself, rather than these other factors, was the driving force behind the reduced ability to keep working.

Perhaps the most revealing part of the research came from looking closely at the twins who were discordant for the disease—meaning one twin had heart disease while the other did not. When the researchers analyzed pairs of identical twins, who share one hundred percent of their genes and the same childhood environment, the link between heart disease and job loss became much weaker and the association was no longer statistically significant. The researchers noted that this lack of significance may reflect sample size limitations rather than a true absence of association, suggesting that while the disease is a significant hurdle, the underlying reasons why some people struggle to return to work may be influenced by inherited factors and early life experiences, rather than the medical event alone.

The findings offer a nuanced view of the challenges faced by workers with heart disease. While the diagnosis is clearly associated with a lower chance of maintaining a long-term career, the study indicates that this association is not solely a direct result of the physical illness. Instead, it is heavily influenced by the complex interplay of family history and shared environmental factors. The researchers noted that their study had limitations, such as a smaller number of identical twin pairs, which meant the results for that specific group should be interpreted with care. Nevertheless, the work highlights that to truly support workers with heart disease, society must look beyond the immediate medical treatment. It suggests that interventions need to consider the broader context of a person's life, acknowledging that genetics and early life conditions play a silent but powerful role in determining who can stay in the workforce and who cannot.