Group Viljakainen

Finnish Health in Teens Study

Fin-HIT – the Finnish Health in Teens – Study is a prospective cohort study including 11 400 Finnish adolescents (9–12 years of age at enrolment) and approximately 10 000 parents. Fin-HIT studies prevalence, risk and protective factors associated with weight status.

Fin-HIT was initiated to follow up weight development from early adolescence to adulthood. Our objective is to study how lifestyle, mental health, family, and microbial, genetic and epigenetic factors interact with the development of weight and health outcomes over time. One of our main topics is to determine if the saliva microbiome is associated with weight status and if so, can it be used for early detection of adolescents at risk of developing overweight and obesity. This has led us to explore the associations between microbiome and lifestyle factors, such as eating habits, antibiotics use and digital use, in order to deepen our knowledge on factors possibly shaping the saliva microbiome.

Baseline data collection was conducted during 2011-2014, mainly in schools by trained fieldworkers. Geographically, a large part of Finland is represented, focusing on densely populated areas. Children answered a questionnaire including questions on e.g. diet, physical activity, body image, sleep and screen time, had their weight, height and waist measured, and provided a saliva sample. The parents answered a web questionnaire.

The first active follow-up with both adolescents and parents was carried out during 2015–2016. The follow-up data consists of self-reported questionnaire, measurement data, and saliva samples from both children and parents. A follow-up allows us to study changes in weight and health, and related associations with microbial and epigenetic changes over time. A second follow-up with a web questionnaire has started in the autumn of 2020. The focus is on nutrition and mental health of the now young adult participants.

The collected research data have been linked to national health registers, which provides us comprehensive health profiles of the participants. The registers are maintained by the Digital and Population Data Services Agency, the Social Insurance Institution of Finland (Kela), the Finnish Institute for Health and Welfare (THL) and Statistics Finland. The saliva samples with selected research data are planned to be stored in the THL Biobank.

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Senior Scientist

Heli Viljakainen, PhD, Docent, Group Leader

Postdoctoral Researchers

Nitin Agrawal, PhD
Sohvi Lommi, PhD
Laura Räisänen, PhD

Doctoral Researcher

Catharina Sarkkola, MSc


Emilia Ankkuri, BAP


Kris Elomaa, MSc, Data Manager
Dylan Pashley, MSc, Data Manager

Agrawal N, Fontana F, Tarracchini C, Lommi S, Ventura M, Milani C, Viljakainen H.
Associations of central obesity and habitual food consumption with saliva microbiota and its enzymatic profiles - a pilot study in Finnish children.
Front Microbiol. 2024 Jan 8;14:1323346. doi: 10.3389/fmicb.2023.1323346. PMID: 38260892; PMCID: PMC10801001.

Viljakainen H, Sorlí JV, Dahlström E, Agrawal N, Portolés O, Corella D.
Interaction between genetic susceptibility to obesity and food intake on BMI in Finnish school-aged children.
Sci Rep 13, 15265 (2023).

Viljakainen H, Engberg E, Dahlström E, Lommi S, Lahti J.
Delayed bedtime on non-school days associates with higher weight and waist circumference in children: Cross-sectional and longitudinal analyses with Mendelian randomisation.
J Sleep Res 2023;e13876.

Räisänen L, Kääriäinen S, Sund R, Engberg E, Viljakainen H, Kolho K-L. 
Antibiotic exposures and the development of pediatric autoimmune diseases: a register-based case–control study.  
Pediatr Res 2022, 19 July.

Lommi S, Manzoor M, Engberg E, Agrawal N, Lakka TA, Leinonen J, Kolho K-L, Viljakainen H. 
The Composition and Functional Capacities of Saliva Microbiota Differ Between Children With Low and High Sweet Treat Consumption
Front. Nutr. 2022, 25 April.

Engberg E, Hietajärvi L, Maksniemi E, Lahti J, Lonka K, Salmela-Aro K, Viljakainen H. 
The longitudinal associations between mental health indicators and digital media use and physical activity during adolescence: A latent class approach. 
Ment. Health Phys. Act. 2022, 22.

Lommi S, Engberg E, Tuorila H, Kolho K-L, Viljakainen H.
Sex- and weight-specific changes in the frequency of sweet treat consumption during early adolescence: a longitudinal study.
Brit J Nutr 2021, Mar 31;1-21.

Raju S, Viljakainen H, Figueiredo RAO, Neuvonen PJ, Eriksson JG, Weiderpass E, Rounge TB. 
Antimicrobial drug use in the first decade of life influences saliva microbiota diversity and composition. 
Microbiome 8, 121 (2020).

Figueiredo RAO, Simola-Ström S, Isomaa R, Weiderpass E. 
Body dissatisfaction and disordered eating symptoms in Finnish preadolescents.
Eating Disorders. Jul 24:1-18.

Institute for Molecular Medicine Finland, Helsinki

Finnish Institute for Health and Welfare (THL)

THL Biobank

CRIG group, Ghent University, Belgium

University of Helsinki, Children’s Hospital

Panic Study, University of Eastern Finland

Department of Psychology and Logopedics, University of Helsinki

Department of Oral and Maxillofacial Diseases, University of Helsinki and Helsinki University Hospital

Laboratory of Probiogenomics, Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Italy

Department of Preventive Medicine, University of Valencia, Spain

Folkhälsan Research Foundation

Research Council of Finland

Medicinska Understödsföreningen Liv och Hälsa (“Life and Health Medical Fund”)

Signe and Ane Gyllenberg Foundation

The Swedish Cultural Foundation in Finland

Yrjö Jahnsson Foundation

Päivikki and Sakari Sohlberg Foundation

Juho Vainio Foundation

Waldemar von Frenckells stiftelse

Finnish Cultural Foundation

Minerva Foundation Institute for Medical Research

Lastentautien tutkimussäätiö


    • Heli Viljakainen

      PhD, Docent, Group Leader

    • Tel:
      +358 50 448 5660

    • Contact