Is mental health affected by a sibling’s cancer diagnosis?

A study by Sara Kjellsson, Kristiina Rajaleid, and Bitte Modin was recently published in PLoS ONE. The findings contribute to the understanding of the ‘spill-over’ effect within sibling relationships when faced with severe illness. It provides insights into the emotional and practical attachments between siblings, emphasizing the need for a family-focused approach in healthcare, especially for adults experiencing adverse life events in their siblings’ lives.

About the study

This study delves into the concept of “linked lives” by emphasizing the impact of social relationships on individuals. Siblings, as enduring and influential relationships, play a vital role in shaping socio-emotional development and contributing to long-term well-being. In this study, we explored the presumed ‘downside’ of linked lives, namely whether the onset of severe illness in one adult sibling tend to ‘spill over’ to affect the other sibling’s health. More specifically, we investigated whether a sibling’s cancer diagnosis increases the risk of developing a psychiatric illness. Two hypotheses were tested: one for the overall relationship between sibling cancer and psychiatric diagnosis, and another for variation by ‘sociodemographic closeness’ between the siblings in the exposed group.

To test our first hypothesis, we used hospital records to identify psychiatric diagnoses (2005-2019) in a Swedish total population cohort born in 1953, and cancer diagnoses (2005-2017) in their full siblings. Through emulated clinical trials, we analyzed the cohort member’s risk of a diagnosis within two years following a first exposure (or non-exposure) to a sibling’s cancer using Cox regression. The second hypothesis was tested by examining whether the risk of psychiatric illness was higher if the siblings were ‘close’ to each other in terms of sex, age, education, marital status and municipality of residence.

Highlights

Our results supported the first hypothesis, namely that individuals who are exposed to a sibling’s cancer diagnosis have a small, but robust, excess risk for subsequent psychiatric illness when relevant covariates have been taken into consideration. Sex-specific analyses also revealed that the hypothesis held true for both genders, but that the association was stronger for men than for women.

The second hypothesis, suggesting that sociodemographic closeness between siblings increases the risk of this type of ‘spill-over’ effects, was only partially supported. Neither for age, place of residence, nor for educational level could any such pattern be detected. However, for sex and marital status, some support was found. Closeness in terms of biological sex increased the ‘spill-over’ effect for women, but not for men. Furthermore, the largest ‘spill-over’ effect was found among unmarried sibling-pairs, while the lowest effect was found among siblings who were both married.

Publication details

Kjellsson S, Rajaleid K, Modin B (2024) Using emulated clinical trials to investigate the risk of being diagnosed with psychiatric ill health following the cancer diagnosis of a sibling. PLoS ONE 19(4): e0298175.

Read more: https://doi.org/10.1371/journal.pone.0298175

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