Britain's longitudinal studies reveal how we are shaped by our beginnings.

Just five decades ago, no one understood that smoking was harmful to babies. That was until results from the 1958 National Child Development Study (NCDS) revealed that mothers’ smoking was associated with reduced birth weight – a key indicator of poor infant health. This finding is lauded as one of the most significant discoveries in longitudinal research and led to extensive investigations into maternal smoking that continue to uncover lifelong adverse effects.

Longitudinal studies follow the same people throughout their lives, uniquely capturing the wide-ranging impact that events and circumstances early in people’s lives can have many years later. Britain’s legacy of national birth cohorts, each of which tracks the lives of people born in a particular time period, began in the aftermath of the Second World War, when giving future generations a better start in life was seen as vitally important. The findings from the first two British birth cohorts – the MRC National Survey of Health and Development (the 1946 birth cohort) and the NCDS – shed light on inequalities in healthcare provision for pregnant women. The quality of antenatal care and conditions at delivery varied considerably between the rich and poor, resulting in increased risk of perinatal mortality for certain groups. These findings had a profound effect on maternity care.

The relationships that these pioneering studies uncovered between childhood circumstances and later outcomes established a tradition of tracking British lives that is now in its eighth decade. More recent studies such as the Millennium Cohort Study and the Southampton Women’s Survey are adding further evidence to what we know about the importance of early life.

The persistence of inequality

Despite hopes that health inequalities would decline with the founding of the National Health Service, evidence from cohort studies points to persistent socioeconomic differences across a wide range of measures of health and wellbeing, including obesity and heart disease.

Longitudinal evidence is not restricted to findings from cohort studies. Understanding Society is an innovative world-leading study about 21st-century UK life and how it is changing. It captures important detail about people’s social and economic circumstances, attitudes, behaviours and health and tracks everyone within a household and is representative of the whole UK population, rather than a specific cohort of people. This gives it considerable scope to add to our understanding of how early circumstances shape later outcomes, and to help measure and understand variations in health and wellbeing. For example, recent research has shown that, despite a significant drop over the last two decades in the number of young people who start smoking, teenagers from socioeconomically disadvantaged backgrounds are twice as likely to experiment with smoking, and more likely to become daily smokers than those from better-off homes.

Longitudinal evidence has shown how environmental influences on our health interact with another ‘condition of birth’ too: genes. Studies like the Avon Longitudinal Study of Parents and Children (ALSPAC), and the biomedical elements of other longitudinal studies, have advanced our understanding of genetics and health immeasurably. Longitudinal research has helped to uncover contributing factors towards obesity and common diseases such as eczema, diabetes, cancer and multiple sclerosis.