Risk factors for sedentary behavior in young adults: similarities in the inequalities.

Early growth and later social circumstances jointly relate to physical activity

A person’s activity level reflects opportunities and constraints across their life. This study asked how conditions at birth and circumstances in young adulthood combined in relation to physical activity in a Brazilian cohort.

Comparing early and later influences. Researchers assessed 2,063 people from the Ribeirão Preto birth cohort at ages twenty-three to twenty-five. A standard physical-activity questionnaire classified participants as active or sedentary; nearly half were classified as sedentary. Separate analyses considered early factors, such as birth weight and maternal circumstances, and later factors, such as the participant’s education, sex, smoking and body mass index. A third analysis combined them.

The birth-weight association changed with context. Low birth weight was associated with sedentary status in the model containing early factors. Once early and later factors were considered together, female sex and lower participant education remained associated with sedentary status, while the simple birth-weight association did not.

An interaction analysis added a different observation: low birth weight was associated with more sedentary behavior among people with higher education. This indicates that the relationship with an early characteristic depended on later social circumstances. It does not mean that education generally reduced activity or that low birth weight was an independent determinant for everyone.

The finding fits the “similarities in the inequalities” framework, in which different life-course combinations can lead to overlapping health-related outcomes. Early biology and later social position may interact rather than contribute a fixed, separate amount of risk.

The study did not directly measure motivation, workplace demands, safety or every opportunity for exercise. Its contribution is to show that developmental and social information need to be considered together when interpreting adult activity patterns, with longitudinal and more detailed exposure measures needed to explain the pathway.