Background: Health, defined by the WHO as a state of complete physical, mental, and social well-being, is important. In adolescents, lifestyle habits such as physical activity, diet, and sleep, have a profound impact on health and are interconnected. These habits among Swedish adolescents vary and could be improved.Aim: The study aims to investigate age- and sex-related differences in self-assessed lifestyle habits and their relation to self-assessed health in Swedish upper secondary school adolescents.

Method: The study included 7535 adolescents, encompassing boys, girls, and those of unknown sex, representing most of the Swedish geography. Self-assessed lifestyle habits and self-assessed health were examined and correlated.

Results: Self-assessed health correlated positively with all variables of self-assessed lifestyle habits. Significant differences were found between boys and girls regarding self-assessed lifestyle habits and self-assessed health, with girls generally reporting lower self-assessed health. Age also significantly influenced self-assessed health and self-assessed lifestyle habits. Irrespective of sex, lifestyle habits showed a negative trend with aging.

Conclusions: Improved self-assessed lifestyle habits correlated positively with better self-assessed health among Swedish upper secondary school adolescents, showing room for improvement, especially among older girls. Future interventions aiming to improve health-related lifestyle habits are necessary.