BMI and Microbiota:
The microbes living in or on humans (the human microbiome) keeps us healthy by digesting food, strengthening the immune system and helping to prevent pathogens from invading tissues and organs. The microbiome plays a major role both in health and disease. Most of the microbiome data available today, is derived from the gut, less is known about the oral microbiome and its association with obesity. The most direct evidence of an oral bacterial association with obesity comes from animal studies. The Fin-HIT microbiome project aim is to determine if the saliva microbiome (microbial community in the saliva) is associated with body size and if so, can it be used for early detection of persons at risk of overweight or underweight. For that, we have extracted the DNA from the saliva samples provided by the participants and sequencing the DNA after amplifying the microbial 16S rDNA from it. Microbiome, obtained by 16S rDNA V3-V4 region sequencing, has been assessed in saliva from 1000 randomly chosen Fin-HIT participants (47 % boys and 53 % girls) at baseline. The ongoing Fin-HIT microbiome study shows significant microbial differences in saliva microbial relative abundance at three taxonomic levels (OTU, Genus, Order) between underweight, normal weight, overweight and obese Finnish adolescents (Raju et al, submitted).
Genomewide DNA-methylation in saliva and body size of adolescent girls:
DNA methylation (DNAm) have an important role for epigenetic gene regulation in development and disease. DNAm is an epigenetic mechanism that occurs by the addition of a methyl (CH3) group to C-5 position of the cytosine ring of DNA, thereby often modifying the function of the genes. When located in a gene promoter, DNA methylation typically acts to repress gene transcription. We performed an epigenome-wide association study within the Finnish Health in Teens cohort to identify differential DNA methylation and its association with BMI in adolescents. Differential DNA methylation analyses of 3.1 million CpG sites were performed in saliva samples from 50 lean and 50 heavy adolescent girls by genome-wide targeted bisulfite-sequencing. We identified 100 CpG sites with p-values < 0.000524, seven regions by ‘bumphunting’ and five CpG islands that differed significantly between the two groups. The ten CpG sites and regions most strongly associated with BMI substantially overlapped with obesity- and insulin-related genes, including MC2R, IGFBPL1, IP6K1 and IGF2BP1. Our findings suggest an association between the saliva methylome and BMI in adolescence (Rounge et al., 2016).
The MetaboChip is a custom Illumina genotyping array designed to test, economical manner, ∼200,000 SNPs of interest for metabolic and atherosclerotic/cardiovascular disease traits. Content on the chip was selected on the basis of large scale meta-analysis of relevant traits and of HapMap and 1000 Genomes Project SNP content. The aim of our study is genotyping the participant children using their saliva samples to identify the risk SNPs with highest effect on body size in Finnish adolescents. DNA from about 1,368 saliva samples were used in this study.
Dietary and meal patterns and body size:
The aim of the study is to identify if body size is influenced by dietary and meal patterns. Groups with different dietary pattern will be constructed by Cluster Analysis considering food frequency questions on diet: dark bread, biscuits or cookies, sweet pastry, pizza, hamburger or hot dog, milk or soured milk, ice cream, cooked vegetables, fresh or grated vegetables and salad, fruits or berries, juice, sugary juice drink, salty snacks, sugary soft drink and water. Body mass index (BMI) has been calculated and the adolescents are classified as underweight, normal weight, overweight and obese according to age and gender specific cut-offs (Cole et al. 2012). (Viljakainen et al., in preparation)
Cole TJ, Lobstein T. Extended international (IOTF) body mass index cut-offs for thinness, overweight and obesity. Pediatr Obes 2012 Aug;7(4):284-294.
Validity of home-measured height, weight and waist circumference among adolescents:
This study assesses the validity of home-measured height, weight and waist circumference among Finnish adolescents in the Fin-HIT cohort. The adolescents were first measured by fieldworkers at school, and were then instructed to measure themselves at home with an adult’s assistance. Paired t-test was used for statistical analyses. Home-measured mean height, weight and waist circumference were slightly higher, but BMI lower than measured by the fieldworker. The difference in means was statistically significant for weight (0.51 kg) and waist circumference (1.6 cm), but not for height and BMI. Home-measured height, weight, waist circumference and BMI are sufficiently accurate to be used in epidemiologic studies (Sarkkola et al, 2016).