It’s a truism that family life, and sibling relationships, can be stressful. But now new light is being shed on why and how this matters. Our research team in Sweden, working with colleagues at University College London, has been looking at whether the shape of our families can affect our ability to cope with stress.
We have found the number of siblings you have can affect your mental – and consequently physical – wellbeing in later life. And the age and sex of your siblings matters, too: in short, older brothers can really stress you out.
Resilience to stress is believed to be key to a healthy life: studies show that if we develop a good ability to cope with stress when young, we are less likely to develop health problems later on. So we know that the patterns and the life-skills we develop in early life can matter a great deal in adulthood. Over recent years, we have produced a growing body of evidence describing links between stress resilience and health: our new Swedish data has been used to look at siblings and follows a whole series of reports on links between the same measure of stress resilience in adolescence and a range of serious conditions in later life.
This research was made possible by the ability to link information from a variety of national records in Sweden, using the unique personal identification number that is issued to all Swedish residents. The first cohort that we created contained information on more than 180,000 men born between 1952 and 1956 who underwent mandatory military conscription between the 1960s and 1970s in Sweden – the vast majority of the country’s male population during that time.
These young men went through a compulsory examination designed to assess their ability to cope with the stress of military action. It involved a 25–30 minute semi-structured interview performed by a licensed psychologist who had access to additional background information, including a self-completion questionnaire. The test produced a nine-point score covering four dimensions: mental energy, emotional control, social maturity and active or passive interests. This information was linked with the health records of those men in later life, to produce a series of research papers which have been published over the past few years.
Even though stress resilience is measured in adolescence, we know that it is a characteristic that persists, at least to middle age. Ayako Hiyoshi and colleagues from Sweden and UCL looked at data on 176,000 of the Swedish military conscripts to see whether those who struggled to deal with stress were more likely to be prescribed drugs for depression or anxiety in their fifties. They found that low stress resilience in adolescence was associated with an increased risk of being on such medication more than 30 years later, and this was not explained by other characteristics relevant to lifestyle.
In 2014, Cecilia Bergh and colleagues in Örebro and at UCL looked at 238,000 of these young men who were then followed up between 1987 and 2010 – by which time they would have been in their late 50s – to see who had suffered from stroke.
Low stress resistance in adolescence was associated with higher stroke risk – and particularly with fatal and haemorrhagic strokes. Although physical fitness levels formed part of the explanation for this, the researchers concluded that effective prevention of strokes might also focus on stress.
The following year Bergh and colleagues, again working with UCL, used the same data on military conscripts to look for an association between stress resilience at age 18 years and heart problems in later life. Low stress resilience was linked with heart disease, and this study extended our understanding of the interplay between stress resilience and physical fitness: the benefit of better fitness to protect from heart disease was reduced in those with low stress resilience.
In 2016 another group of academics at Lund in Sweden and at Stanford in the US reported on a study using an even bigger dataset of 1.5 million men who were conscripts between the late 1960s and the late 1990s in Sweden. This time they looked for an association between stress resilience and type two diabetes. They identified who had been diagnosed with type two diabetes by their early sixties. Even after adjusting for body mass index (BMI), family history of diabetes and socioeconomic factors, those who coped well with stress were less likely to develop type two diabetes.
We believe there is a common link between these findings – that low resilience is likely to signal a greater tendency to chronic stress arousal, with both behavioural and metabolic consequences that are harmful to health. Stress resilience even appears to be relevant to survival after a cancer diagnosis.
But how does that lowered resilience to stress arise in the first place? What puts young people in a position which exposes them to such a wide variety of serious health risks?
More recently, new data linkage has been undertaken to examine the factors in earlier life that may explain why some people have low stress resilience in adolescence. The new dataset contains information on over 3.2 million men and women who were born in Sweden between 1970 and 2000.
In some ways our newest research output in this strand might seem rather depressing, as the problem it identifies is not easy to fix – it finds that childhood experiences signalled by the presence of older siblings, particularly older brothers, may have important implications for both stress resilience and cognitive function, and thus for adult health.
In this latest study we followed 664,000 of the men who were born between 1970 and 1992 and underwent the conscription assessment between 1987 and 2010 with tests of stress resilience and cognitive function. We examined whether the numbers of older male or female siblings they had or the socioeconomic position (ESeC) of their parents could be associated with their test results.
Having a larger number of older brothers had a greater association with low stress resilience than having older sisters. One of the reasons we looked at sex of siblings is there is separate research from Italy showing that working mothers were more likely to suffer from heart disease if they had sons rather than daughters.
While socioeconomic characteristics could partially explain the effect (bigger families are more likely to experience socioeconomic disadvantage), there was still a significant association with siblings after taking this and other factors into account. Having older siblings, particularly older brothers, was also associated with lower cognitive function test scores, but this might be expected as lower stress resilience is linked with lower cognitive function.
Why might this be? We suggest older children may have greater access to family resources including parental attention. Also, older brothers may be in the most dominant position and therefore more able to bully their younger siblings – who may then perceive their environment as more threatening. That, we think, may have implications for their stress resilience. These exposures could potentially influence development through both psychological and neuroendocrine pathways.
There are some potential limitations to this research – it only looks at ostensibly healthy males and excludes those who were exempted from military service. The men’s stress resilience was only measured at one point – when they were assessed for military service. And we can’t identify inherited susceptibility factors that might modify the consequences of childhood experience.
But despite potential limitations, there is a strong message from the research: older brothers should not be demonised, but there are ways in which the most stressful aspects of family life, including sibling rivalry and bullying, can be mitigated. We conclude that these issues should be examined and, if possible, reduced. We now know they can have serious and lifelong consequences.
Scott Montgomery is Professor of Clinical Epidemiology at Örebro University Hospital & Örebro University in Sweden with an attachment to the Karolinska Institute, He is also an honorary professor at UCL. Sex of older siblings and stress resilience, by Scott Montgomery, Cecilia Bergh, Ruzan Udumyan, Mats Eriksson, Katja Fall and Ayako Hiyoshi is published in Longitudinal and Life Course Studies 2018 Volume 9 Issue 4 Pp 447–455 ISSN 1757-9597 447.
Image credit: U.S. Air Force photo/Staff Sgt. Luis Loza Gutierrez