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Background: Dietary choices are shaped by both genetic predisposition and environmental exposures, yet the relative influence of these factors remains insufficiently understood across populations and age groups. Young adulthood represents a critical period when long-term eating habits take form, and clarifying the determinants of dietary behavior in this life stage may inform strategies to promote sustained health.

Objectives: This twin study aimed to estimate genetic and environmental contributions to food, energy, and nutrient intakes, and taste preferences in young adults in Sweden.

Methods: The study included 2832 Swedish twins (858 monozygotic and 1974 dizygotic; mean age 24 y; 59.5% female). Participants completed a validated dietary questionnaire assessing food intake frequencies and taste preferences. Additive genetic (A), shared environmental (C), and nonshared environmental (E) influences on a priori dietary indices, specific food and nutrient intakes, and taste preferences were estimated using classical ACE twin models and nested models fitted in OpenMx.

Results: Heritability estimates across dietary traits ranged from 20% to 61%. Genetic influences on overall dietary pattern indices exceeded 40%. Heritability varied across food groups (e.g., 61% for venison; 24% for potatoes) and nutrient intakes (50% for fiber; 20% for sodium), indicating differing degrees of genetic impact across dietary components. Taste preferences also showed substantial genetic contributions (21%–61%), with the strongest effects observed for bitter foods (e.g., black coffee, grapefruit), followed by sweet foods (e.g., jam/marmalade).

Conclusions: This large-scale twin study provides a comprehensive overview of genetic and environmental influences on dietary behavior in young adults, showing substantial genetic and nonshared environmental contributions across diverse dietary traits. These results provide a foundation for future research on diet–disease relationships and may support the development of prevention and intervention strategies, including emerging precision-nutrition approaches.

We assessed hepatocellular carcinoma (HCC) risk associated with smoking and alcohol consumption and their interactions, using both questionnaire data and objective serum biomarkers. Information on smoking and alcohol consumption was collected at baseline from 450,112 participants of the EPIC cohort, among whom 255 developed HCC after a median follow-up of 14 years. In a nested case–control subset of 108 HCC cases and 108 matched controls, known biomarkers of smoking (cotinine, nicotine) and habitual alcohol consumption (2-hydroxy-3-methylbutyric acid) were annotated from untargeted metabolomics features. Multivariable-adjusted hazard ratios (HRs) or odds ratios (ORs) with 95% confidence intervals (CIs) were computed, and multiplicative and additive interaction parameters were calculated. Compared to never smokers, current smokers had a higher HCC risk (HR = 2.46, 95% CI = 1.77–3.43) dose-dependently with the number of cigarettes smoked per day (Ptrend <.001). Compared to light drinkers, HCC risk was higher in former (HR = 3.20, 95% CI = 1.70–6.03), periodically heavy (HR = 1.98, 95% CI = 1.11–3.54), and always heavy (HR = 5.51, 95% CI = 2.39–12.7) drinkers. Higher HCC risk was also observed in the highest versus the lowest tertiles of cotinine (OR = 4.88, 95% CI = 1.52–15.70), nicotine (OR = 5.80, 95% CI = 1.33–25.30) and 2-hydroxy-3-methylbutyric acid (OR = 5.89, 95% CI = 1.33–26.12). Questionnaire-assessed smoking and alcohol exposures did not demonstrate an HCC risk interaction at the multiplicative (MI = 0.88, 95% CI = 0.40–1.96) or additive (RERI = 0.71, 95% CI = −10.1 to 23.6; attributable proportion = 0.17, 95% CI = −0.52 to 1.16; synergy index = 1.27, 95% CI = 0.98–1.66) scales. Similar analyses with cotinine, nicotine, and 2-hydroxy-3-methylbutyric acid also did not show interactions between smoking and alcohol consumption on HCC risk. Smoking and alcohol consumption are strong independent risk factors for HCC and do not appear to synergistically impact its risk, but larger studies are needed.

Background: Dietary habits strongly influence health, with poor diets contributing to numerous deaths annually. Addressing this requires improved dietary habits and consistent monitoring thereof. In northern Sweden, a validated food frequency questionnaire (FFQ) has been used for decades, but trends show that its ability to accurately measure intake has diminished. With changing eating habits and food supply, updating the FFQ was crucial, leading to the development of FFQ2020. This study assessed FFQ2020’s relative validity using 24-hour recalls and evaluated its reproducibility.

Methods: Participants were recruited from one of the northern-Sweden population-based health screenings and by advertising. Food intake was registered in an electronic food frequency questionnaire (FFQ2020) (test instrument) and reference data were obtained by six repeated electronic 24-hour dietary recalls (24HDR). Intakes of single foods were aggregated into food groups and healthy diet index scores, and daily energy and nutrient intakes were estimated. Results from the two methods were described and tested in univariate analyses and correlation tests, Bland Altman plots, cross-classification validity, and intra-class correlation analyses.

Results: Totally, 628 adults were invited to participate in the study. Of these, 320 joined, and 244 completed at least four 24HDRs. The median intakes in food groups, as well as the mean index scores and estimated nutrient intakes, were largely similar between the FFQ2020 and 24HDR recordings. The correlation coefficients between the two assessments ranged from 0.253 to 0.693 for food groups, 0.520 to 0.614 for diet indices, and 0.340 to 0.629 for energy and nutrients. Intra-class correlation coefficients indicated at least good reproducibility for intakes of food groups, diet index scores, and nutrients. Generally, Bland-Altman plots did not reveal any gross systematic disagreement between the two methods for any of the assessments. However, there were single observations located outside the upper or lower 95% confidence interval (CI) limits for the difference between FFQ2020 and the 24HDR recordings.

Conclusion: In concert, the results suggest that the relative validity and reproducibility of FFQ2020 are acceptable for trend analyses and group comparisons in large-scale studies but also that extended reference periods would improve the precision of less frequently consumed foods.

Background: Dietary pattern analysis has gained particular interest, because it reflects the complexity of dietary intake. The aim of this study was to explore the associations between a posteriori dietary patterns, derived using a data-driven approach, and the risk of differentiated thyroid cancer (TC) in Europe.

Methods: This investigation included 450,064 adults from the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. Dietary intake was assessed using validated country-specific dietary questionnaires. A posteriori dietary patterns were computed using principal component analyses. Cox regression was used to calculate multivariable adjusted hazard ratios (HRs) and 95% confidence intervals (CIs).

Results: After a mean follow-up time of 14 years, 712 first differentiated TCs were diagnosed. In the fully adjusted model, a dietary pattern characterized by alcohol consumption (basically beer and wine) was negatively associated with differentiated TC risk (HR_Q4vs.Q1 = 0.75; 95% CI:0.60–0.94, P-trend = 0.005), while a dietary pattern rich in sweetened beverages was positively associated with differentiated TC risk (HRQ_4vs.Q1 = 1.26; 95% CI:0.99–1.61; P-trend = 0.07). The remaining 8 dietary patterns were not related to differentiated TC risk. The intake of sweetened beverages was positively associated with differentiated TC risk (HR_100mL/d = 1.05; 95% CI:1.00–1.11), especially with papillary TC risk (HR_100mL/d = 1.07; 95% CI:1.01–1.13). Similar results were observed with sugary and artificially sweetened beverages.

Conclusions: The investigation of dietary patterns detected that the consumption of sweetened beverages was associated with a higher risk of differentiated thyroid cancer. Our results are in line with the general dietary recommendations of reducing the consumption of sweetened beverages.

Objectives: The oral microbiota plays a significant role in oral health. The present study aims to characterize variations in the oral microbiota relative to the collection site, the dynamics of biofilm accumulation, and inherent inter-individual differences.

Methods: Whole stimulated saliva and tooth biofilm samples from the 16 defined tooth regions were collected after 1, 2, or 3 days without oral hygiene (accumulation time) in six healthy adults with no signs of active caries or periodontal disease. The routines and conditions before and between sample collections were carefully standardized. Genomic DNA was extracted, and the V3-V4 regions of the 16S rRNA gene were amplified by PCR and sequenced on an Illumina MiSeq platform. Sequences were quality controlled, amplicon sequence variants (ASVs) were clustered, and taxonomic allocation was performed against the expanded Human Oral Microbiome Database (eHOMD). Microbial community profiles were analyzed by multivariate modeling and a linear discriminant analysis (LDA) effect size (LEfSe) method.

Results: The overall species profile in saliva and tooth biofilm differed between participants, as well as sample type, with a significantly higher diversity in tooth biofilm samples than saliva. On average, 45% of the detected species were shared between the two sample types. The microbiota profile changed from the most anterior to the most posterior tooth regions regardless of whether sampling was done after 1, 2, or 3 days without oral hygiene. Increasing accumulation time led to higher numbers of detected species in both the saliva and region-specific tooth biofilm niches.

Conclusion: The present study confirms that the differences between individuals dominate over sample type and the time abstaining from oral hygiene for oral microbiota shaping. Therefore, a standardized accumulation time may be less important for some research questions aiming at separating individuals. Furthermore, the amount of DNA is sufficient if at least two teeth are sampled for microbiota characterization, which allows a site-specific characterization of, for example, caries or periodontitis.

Excessive sucrose consumption is associated with numerous health problems, including dental caries, and is considered to play a critical role in shaping the human microbiota. Here, we aimed to confirm the association between sucrose exposure and oral microbiota profile, develop a short food-based index capturing variation among sucrose consumers and validate it against oral microbiota and dental caries in a derivation cohort with 16- to 79-year-old participants (n = 427). Intake and food preferences were recorded by questionnaires and saliva microbiota by 16S rDNA sequencing. Taxonomic similarities clustered participants into five clusters, where one stood out with highest sucrose intake and predicted sugar related metabolic pathways but lowest species diversity in the microbiota. Multivariate modelling of food intake and preferences revealed foods suitable for a sucrose index. This, similarly to sucrose intake, was related to bacterial pattern and caries status. The validity of the sucrose index was replicated in the population-based Gene-Lifestyle Interactions in Dental Endpoints (GLIDE, n = 105,520 Swedish adults) cohort. This suggested that the index captured clinically relevant variation in sucrose intake and that FFQ derived information may be suitable for screening of sucrose intake in the clinic and epidemiological studies, although adjustments to local consumption habits are needed.

Corynebacterium matruchotii may be key in tooth biofilm formation, but information about demographics, bacterial partners, and binding ligands is limited. The aims of this study were to explore C. matruchotii's demography by age and colonization site (plaque and saliva), in vitro bacterial-bacterial interactions in coaggregation and coadhesion assays, and glycolipids as potential binding ligands in thin-layer chromatogram binding assays. C. matruchotii prevalence increased from 3 months to 18 years old, with 90% and 100% prevalence in saliva and tooth biofilm, respectively. C. matruchotii aggregated in saliva in a dose-dependent manner but lacked the ability to bind to saliva-coated hydroxyapatite. In vivo, C. matruchotii abundance paralleled that of Actinomyces naeslundii, Capnocytophaga sp. HMT 326, Fusobacterium nucleatum subsp. polymorphum, and Tannerella sp. HMT 286. In vitro, C. matruchotii bound both planktonic and surface-bound A. naeslundii, Actinomyces odontolyticus, and F. nucleatum. In addition, C. matruchotii exhibited the ability to bind glycolipids isolated from human erythrocytes (blood group O), human granulocytes, rabbit intestine, human meconium, and rat intestine. Binding assays identified candidate carbohydrate ligands as isoglobotriaosylceramide, Gal alpha 3-isoglobotriaosylceramide, lactotriaosylceramide, lactotetraosylceramide, neolactotetraosylceramide, and neolactohexaosylceramide. Thus, C. matruchotii likely uses specific plaque bacteria to adhere to the biofilm and may interact with human tissues through carbohydrate interactions.

Background: Dental caries still appears at high prevalence worldwide. Disease distribution is skewed with more disease in socio-economically weak groups. However, also in populations considered as “low caries” there is a significant fraction with continuous disease development. Caries develops when the hard tissues of the tooth is demineralized, which occurs when pH drops below approximately 5.5 for enamel and 6.2 for dentine. The pH drop follows fermentation and acid production by tooth colonising bacteria upon dietary carbohydrate exposure. Thus, understanding the interactions between oral bacteria, diet and host factors is essential for managing the disease. The overall aim of this thesis was to study the oral microbiota in relation to caries and its association with sugar intake and driving forces behind sugar intake.

Material and method: Saliva and tooth biofilm samples, information on caries status, dietary habits and other lifestyle data were collected from 17-23 year old participants. The participants also carried out a tasting session for the tastes sour, sweet and bitter. Genomic DNA was extracted from saliva and tooth biofilm and analysed using 16S rDNA amplicon sequencing with two platforms. Taxa were classified against the eHOMD database. Taste gene genotyping was done by mass spectrometry. Data were compared by univariate and multivariate statistical methods.

Results: Oral microbiota was analysed in 64 adolescents. Streptococcus mutans, Scardovia wiggsiae, Bifidobacterium longum and Lepotrichia sp. HOT 498 displayed strong association with having caries, whereas Corynebacterium matruchotii and tooth brushing were associated with being caries-free. It was also confirmed that S.mutans was not compulsory for having caries. The oral microbiota in caries affected adolescents without S. mutans in was evaluated, and found to be characterised by a wide panel of saccharolytic non-S.mutans species. In contrast, tooth biofilms in individuals with caries and S. mutans were enriched for relatively few saccharolytic species in addition to S.mutans. Further, the overall microbiota pattern fell into four distinct clusters with deviating caries prevalence. The association with a set of lifestyle factors was searched, and sugar intake was found to differ between the groups. In the cluster with the highest sugar intake, the microbiota was less diverse and low sugar intake was characterized by enumeration of C. durum, C. matruchotiiand S. sanguinis. To deepen the knowledge on mechanisms behind sweet food intake, single nucleotide polymorphisms (SNP) genotyping in genes reported to be associated with taste regulation or sugar intake was done. SNPs in four genes were associated with sensitivity and preference for sweet taste and in the SLC2A2 gene also with caries.

Conclusions: This project confirmed that dental caries is not a single species disease, and in the present population S. mutans, S. wiggsiae, and B. longum were significant for having caries. It was also confirmed that S. mutans is not essential for having caries. Tooth biofilm microbiota in S. mutans free adolescents was characterised by a larger diversity of species than seen in those with caries and S. mutans. It may be hypothesised that sugar intake and associated pH drops alone or in interaction with host biology play a role in the differentiation of the microbiota into the distinct profiles. This was supported by the finding that sugar intake was related to microbiota clustering and less community diversity. In this perspective the genetically based influence on sugar preference should be taken into account in dietary counselling which is an important aspect in caries prevention and treatment.

Taste and diet preferences are complex and influenced by both environmental and host traits while affecting both food selection and associated health outcomes. The present study genotyped 94 single nucleotide polymorphisms (SNPs) in previously reported taste and food intake related genes and assessed associations with taste threshold (TT) and preferred intensity (PT) of sweet, sour and bitter, food preferences, habitual diet intake, and caries status in healthy young Swedish men and women (n = 127). Polymorphisms in the GNAT3, SLC2A4, TAS1R1 and TAS1R2 genes were associated with variation in TT and PT for sweet taste as well as sweet food intake. Increasing PT for sweet was associated with increasing preference and intake of sugary foods. Similarly, increasing TT for sour was associated with increasing intake of sour foods, whereas the associations between food preference/intake and TT/PT for bitter was weak in this study group. Finally, allelic variation in the GNAT3, SLC2A2, SLC2A4, TAS1R1 and TAS1R2 genes was associated with caries status, whereas TT, PT and food preferences were not. It was concluded that variations in taste receptor, glucose transporter and gustducin encoding genes are related to taste perception, food preference and intake as well as the sugar-dependent caries disease.

Streptococcus mutans is a key bacterial species in the caries process, which affects >90% of the population worldwide. However, other acidogenic and aciduric/acidophilic species may contribute to disease development. In Sweden, a country with low prevalences of caries and S. mutans, a significant portion of caries-affected adolescents lack detectable levels of S. mutans. The objectives of the present study were 1) to characterize the tooth biofilm and saliva microbiota of adolescents with caries disease, with or without detectable S. mutans, from tooth biofilm and saliva samples and 2) to assess taxa clustering in the tooth biofilm and saliva samples and relate this information to caries status. For 17-y-old participants ( N = 154), enamel and dentin caries (the total number of present carious surfaces in the enamel and dentin) and caries experience (the number of decayed and filled tooth surfaces) were recorded, dental biofilm and saliva samples obtained, and information on medical and lifestyle habits collected. Multiplex 16S rDNA (V3-V4) sequencing of bacterial DNA was performed with the Illumina MiSeq platform. The Human Oral Microbiome Database and the ProbeSeq pipeline were used in the HOMI NGS procedure. In subjects with caries experience, high levels of S. mutans were associated with a few species and low levels with a panel of saccharolytic species. Present caries was similarly associated with a panel of saccharolytic species in subjects without S. mutans. Furthermore, tooth biofilm microbiota could be used to establish 4 clusters of subjects with different caries experiences. In particular, high levels of S. mutans were associated with the presence of a few influential species in multivariate modeling, including Scardovia wiggsiae. By contrast, a panel of less avid lactic acid-producing species was influential in patients with undetectable or low S. mutans levels in such modeling. These findings support a prominent role of S. mutans in infected adolescents but also the ecologic concept, especially in S. mutans-free subjects.