The main aim of Fin-HIT is to explore risk and protective factors for excess weight / weight gain. Therefore, we need objective measures of body size and shape such as height, weight and waist circumference. Body mass index (BMI; kg/m2) is a widely used measure to determine overweight and obesity in children and adolescents. However, BMI is more complicated to use among children than adults, since it depends on age and sex, and it is often referred to as BMI-for-age or BMI z-score.
There are two international reference values to classify underweight, normal weight, overweight and obesity in children: the International Obesity Task Force (IOTF) and the WHO growth reference. The prevalence of overweight is slightly overestimated by the WHO growth reference 2007 compared with the IOTF. IOTF incorporates survey data from Brazil, Great Britain, Hong Kong, Singapore, United States, and The Netherlands and is currently utilized in our cohort.
Waist-to-height ratio, calculated by dividing the waist circumference (WC) by height, has recently gained attention as a measure for central obesity in children. The waist-to-height ratio may have an advantage over BMI, which does not provide any information about body fat distribution or body shape. It is considered a more reliable predictor of cardiovascular disease risk in children and adolescents than BMI.
A commonly used measure in Finland is weight-for-height. New Finnish references for weight-for-height were constructed in 2011.
The microbes living in or on humans (the human microbiome) keep us healthy by digesting food, strengthening the immune system and helping to prevent pathogens from invading tissues and organs. The microbiota plays a major role in both health and disease. Most of the microbiota studies have focused on gut, but less is known about the oral and saliva microbiota: their determinants and possible associations with various health outcomes are yet to be explored.
In humans, different salivary bacteria were found between vegans and omnivores (plant- and animal-based diet). We are aiming to identify saliva bacteria that is linked to the development of obesity or signs of metabolic syndrome. In addition, we are exploring different determinants of saliva microbiota diversity and composition (e.g. diet, antimicrobial drugs, oral health, host genetics). Recently we found a significant difference in microbial diversity and composition in saliva and differently abundant bacteria between body sizes compared with normal weight. The findings will have several implications including technological innovations, but also involve practices in health care and dental services.
Beyond other factors, genetic variants are a contribution to weight development and BMI. Common obesity is a complex trait, that is affected by multiple common genetic variants, which are likely to interact together and/or with lifestyle factors, thus modifying our susceptibility to weight gain. To date, over 100 common genetic variants have been consistently linked with BMI, but together they explain less than 3% of the variation in adult BMI. One of such variants is fat mass- and obesity-associated gene (FTO). More interestingly, the impact of genetic variants on BMI may vary during the life course.
There are situations in which obesity results from the mutation or defect in a single gene (monogenetic obesity). These are rare, early-onset, extreme conditions that may present with additional clinical features including endocrine and mental disorders.
Epigenetic alterations are suspected to contribute to the development of obesity. Epigenetic processes involve altering gene activity without altering the DNA sequence, resulting in phenotypic changes, such as obesity. DNA methylation, the most well studied epigenetic mark, is affected by various lifestyle factors. The epigenetic changes process occurs gradually with ageing, smoking, antibiotics, air pollution, and others.
Currently, we are interested to identify important genetic and epigenetic factors and evaluate how they are associated with weight gain and obesity in adolescents.
Poor diet and eating habits during childhood are major contributing factors for various noncommunicable diseases. Eating habits are affected by personal preferences as well as cultural, religious, economical, environmental, and even political factors. Adolescence is a transition period and during that time eating habits evolve.
The traditional Finnish foods are, among others, milk or sour milk, cooked vegetables and dark grain bread, which are part of a healthy diet. Typical Finnish meal pattern consists of a breakfast, a warm lunch, a warm dinner, and two snacks. Finnish children receive a daily warm lunch at school for free, which is very unique to have, even in Nordic countries. There is room for improvement in adolescents’ diets though: on average, they consume insufficiently fruits and vegetables, and favour sugary foods and soft drinks.
Adolescents’ craving for sugar can partly be blamed for innate preference for sweet taste, driven by genetics and modified by an exposure to sweet foods. Preference for sweet taste is at strongest in childhood but it decreases with age. Children and adolescents’ sugar consumption is of concern as it can deteriorate dietary quality, have adverse health effects and lead to weight gain. Sugary foods and drinks are typically energy-dense and nutrient-poor, and can replace more nutritious foods in the diet. Especially sugar-sweetened beverages are troublesome as they do not promote satiety response the same way as sugar in a solid form does.
Food consumption can be measured with various methods and on several levels. We have used a food frequency questionnaire that indicates how many times a week the respondent eats or drinks certain food items. We are interested in associations of different eating behaviours with weight status, weight gain, and other health outcomes in adolescents.
Physical activity and screen time
Physical activity can be defined as any bodily movement produced by the contraction of skeletal muscles that increases energy expenditure above a basal level. Exercise, in the other hand, refers to physical activity that is planned, structured, repetitive and performed with the goal of improving health or fitness. In short, all exercise is physical activity, but not all physical activity is exercise.
Sedentary behaviour (from the Latin sedere, ‘to sit’) refers to any waking behaviour that does not increase energy expenditure substantially above the resting level while sitting, reclining or lying (e.g. sitting in an automobile). Further, sedentary screen time refers to the time spent using a screen-based devise (e.g. smartphone, tablet, computer, television) while being sedentary (= sitting, reclining or lying).
In the Fin-HIT, we have assessed both the children’s and their guardians’ physical activity and screen time with a questionnaire when the children were around 9-12 years old and again at a follow-up when they were 13-15 years old. The purpose is to examine whether and how physical activity and screen time are related to weight, weight gain and other aspects of the children’s health.
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