A life of loneliness threatens aspects of someone's health as much as physical inactivity in adolescence or diabetes in old age, new research claims.
Lacking a network of friends or family can "vastly elevate" the risk of developing health conditions and can affect physical well-being down the line.
Scientists examined links between relationships and healthiness across each life stage, looking at a variety of factors including body-mass index (BMI).
It found that weak social relationships in younger years increases the risk of inflammation at the same rate as a lack of exercise.
Similarly, hypertension in old age is exacerbated more by loneliness than clinical risk factors such as diabetes.
But those blessed with the support of friends and loved ones have a lower likelihood of developing health conditions and boast better life expectancy.
The study, published in the Proceedings of the National Academy of Sciences journal, said: "We found that a higher degree of social integration was associated with lower risk of physiological dysregulation in a dose-response manner in both early and later life.
"Conversely, lack of social connections was associated with vastly elevated risk in specific life stages.
"Analyses of multiple dimensions of social relationships within multiple samples across the life course produced consistent and robust associations with health.
"Physiological impacts of structural and functional dimensions of social relationships emerge uniquely in adolescence and midlife and persist into old age."
During adolescence especially, BMI and waist circumference were found to be higher among those with lower levels of social integration.
Having a strong social base earlier in life also has a bearing on well-being in later years, with one of the four studies examined finding a 54 per cent reduction in the chances of developing hypertension.
Using data collected from four large longitudinal studies of US residents, researchers believe their report sheds new light on the link between the social and the biological.
