The Finnish Health in Teens study – Fin-HIT- is a cohort study including more than 10,000 Finnish adolescents aged around 9-12 years at enrolment, together with 10,000 guardians, the vast majority mothers. This age range was chosen as the majority of participants are about to enter puberty and are cognitively mature to participate in the study according to our own focus group discussions.

Fin-HIT studies prevalence, risk and protective factors associated with body size. We have on-going studies of potential associations between body size, epigenetic factors and microbiome. One of our overall study aims is to determine if the saliva microbiome is associated with body size and if so, can it be used for early detection of adolescents at risk of developing overweight and obesity.

The Ethics Committee of the Hospital District of Helsinki and Uusimaa has approved the Fin-HIT study.

Cohort recruitment

The participants were recruited and baseline data collection was performed during 2011-2014.

Pilot study: Home recruitment, by mailed invitations to 11,000 selected households, was tested in 2011. The response rate using this strategy was 14 %. A phone interview study done amongst 166 randomly selected non-participating guardians indicated that the main reason for non-participation was lack of time (43 %).

Main study:<The largest part of recruitment was therefore conducted in the schools where trained fieldworker teams presented the study in school classes and handed out invitations to the adolescents. At school, the adolescents answered a questionnaire on an electronic tablet pc, provided a saliva sample and had their height, weight and waist circumference measured in a standardized way by the fieldworkers. Saliva samples were collected using Oragene® DNA Self-Collection Kit. Guardians participated by answering a web questionnaire.

A total of 27,000 households was invited during the school recruitment. The participation rate for
the adolescents at baseline was 36 %. In total 496 schools, and 1,415 school classes participated throughout Finland, including rural and urban areas (see map). 95 % of the schools approached accepted to participate in the study.


The current ethical approval for follow-up is 25 years which all participants have consented to.

The first active follow-up

During 2015-2016, the households were invited to the first follow-up, when the majority of adolescents are 13-15 years old. A follow up allows us to study changes in body size and health status in the participants over time, including microbiotic and epigenetic changes in body size development. The invited adolescent and guardian were both asked to answer a web questionnaire, give a saliva sample and to report their height, weight and waist circumference.

Register linkage

The participants have consented to link their study data to national health registers. The registers include Population Information System at the Population Register Center (PRC; data such as social security number, address, mother tongue), The Social Insurance Institution of Finland (Kela; data such as medicine prescriptions, purchase of medicine, medicine expenses), Statistics Finland (data such as occupational status, wages, cause of death) and the National Institute for Health and Welfare (THL; data such as pregnancy, new-born health, diagnoses).