One of the great public health challenges in today’s society is the rising prevalence of overweight and sedentary behaviour. Overweight is a multifaceted condition that contributes to a wide array of chronic diseases, including cancer, diabetes and cardiovascular diseases (American Diabetes Association Professional Practice Committee, 2023; Bianchini et al., 2002). The causes of obesity are complex and multifaceted, with various mediating factors. Individual differences can explain some of the variations in overweight across individuals. In recent decades, research has established associations between the Big Five personality traits, health behaviours and clinical outcomes (Turiano et al., 2015; Sutin et al., 2011; Wimmelmann et al., 2018; Jokela et al., 2013; Lunn et al., 2014). Extraversion, Agreeableness, and Openness have been associated with health in previous research, but these associations tend to be weaker and less consistent (Shim et al., 2014; Sutin et al., 2011). Therefore, focuses this study on Neuroticism and Conscientiousness, as they show more consistent associations with health, likely due to their relevance for emotional reactivity and self-regulation (Sutin et al., 2011). Neuroticism reflects the individual’s emotional stability and resistance to pressures from the surrounding environment. High Neuroticism scores indicate stronger reactions to negative life events and stressors (Simonsen et al., 2017), whereas individuals with low Neuroticism scores are in general more emotionally stable and less reactive to stressful conditions (Dammeyer & Zettler, 2018; Pedersen et al., 2024). Conscientiousness represents the individual’s competence to be organised, goal-oriented, the degree of work ethic attitude and attention to details (Dammeyer & Zettler, 2018; Pedersen et al., 2024). Individuals with low Conscientiousness scores tend to be less focused on long-term goals, more impulsive, and may struggle with motivation and following through on commitment (Dammeyer & Zettler, 2018; Pedersen et al., 2024). A growing body of evidence suggests that Conscientiousness is positively associated with health behaviours and health-related outcomes, whereas Neuroticism is negatively associated (Atherton et al., 2014; Friedman et al., 2014; Bogg and Roberts, 2004; Weston et al., 2015). High Neuroticism has been associated with higher BMI, greater weight gain and increased weight fluctuations over time, whereas high Conscientiousness appears to have a protective effect against a high BMI (Sutin et al., 2011; Jokela et al., 2013; Sutin and Terracciano, 2016; Sutin and Terracciano, 2017; Sutin et al., 2015; Vainik et al., 2019). However, the underlying mechanisms remain insufficiently investigated. In particular, evidence on how health behaviours mediate these associations, and whether such pathways vary by socio-demographic factors such as educational level, remains limited (Turiano et al., 2018; Hampson et al., 2007). Even though BMI is widely used as a proxy for health, it has been noted to have limitations, particularly in distinguishing between fat mass, muscle mass, and metabolic health, and should therefore be interpreted with caution (Franco et al., 2025).

Behavioural determinants, including physical activity, dietary habits and meal patterns have been found to explain approximately 50% of the association between Neuroticism, Conscientiousness and BMI (Sutin and Terracciano, 2016). This highlights the need for increased focus on behavioural determinants such as eating behaviour and physical activity to reduce the increasing prevalence of overweight. Studies investigating associations between physical activity and the Big Five personality traits have found that Neuroticism is negatively associated with physical activity (Tolea et al., 2012; Rhodes and Smith, 2006; Sutin et al., 2016; Wilson and Dishman, 2015), whereas individuals with high Conscientiousness tend to be more physically active and engage in less sedentary behaviour (Sutin et al., 2016). Research examining exercise intensity preferences indicates that individuals with high Neuroticism tend to prefer low-intensity exercise activities, whereas those with high Conscientiousness are more likely to prefer high-intensity exercise (Hagan and Hausenblas, 2005), which has several health-related benefits.

Research on the Big Five personality traits and eating behaviour shows that high Neuroticism and low Conscientiousness are associated with emotional eating (Elfhag and Morey, 2008), whereas low Neuroticism and high Conscientiousness are associated with restrained eating (Elfhag and Morey, 2008). Other research has demonstrated that Neuroticism is associated with a preference for salty foods, sweets, a lower intake of fruits and vegetables, higher consumption of sugar and saturated fats (Esposito et al., 2021), and a greater preference for convenience food (Mõttus et al., 2013). Individuals with low Neuroticism are in general better at resisting food cravings and binge eating (Sutin et al., 2011). Additionally, a preference for the Mediterranean diet and greater health awareness have been found to be positively associated with Conscientiousness (Mõttus et al., 2013). Overall, an individual’s personality trait appears to influence dietary choices and diet-related awareness.

The literature presents conflicting findings regarding the association between Neuroticism and health-related outcomes. While high Neuroticism is often associated with adverse health behaviours, some studies suggest it may also be associated with reduced mortality risk, and lower levels of inflammation markers, potentially mediated by increased physical activity (Weiss and Costa, 2005; Graham et al., 2018). These contrasting results of Neuroticism have led to the theory of Healthy Neuroticism (Friedman, 2000). Healthy Neuroticism is not defined consistently across studies, some researchers have investigated Healthy Neuroticism as the interaction of socioeconomics factors and sex on Neuroticism (Hagger-Johnson et al., 2012; Graham et al., 2020), whereas the majority of studies investigate the interaction of Neuroticism and Conscientiousness. Studies indicate that individuals with high Neuroticism and low Conscientiousness, are more likely to engage in undesirable health behaviours, such as smoking, exhibit higher levels of the inflammation marker interleukin 6 (IL-6), which may be driven by these undesirable behaviours, compared to individuals who score high on both Neuroticism and Conscientiousness (Healthy Neuroticism) (Weston and Jackson, 2014; Turiano et al., 2013). A series of three separate papers investigated the impact of Healthy Neuroticism on longevity, chronic diseases, and health behaviours (Graham et al., 2020; Turiano et al., 2020; Weston et al., 2020). One of the papers reported that high Conscientiousness may protect against the risk of smoking among individuals with high Neuroticism. It also found that individuals high in Neuroticism and low in Conscientiousness were more likely to be physically inactive (Graham et al., 2020). However, research on Healthy Neuroticism is still sparse, not least in the field of health behaviours, such as physical activity and dietary choices.

A better understanding of the complex relationship between Neuroticism, Conscientiousness, and health behaviours may be essential for effectively support individuals in improving BMI, physical activity, and dietary habits. While existing literature suggests that Neuroticism and Conscientiousness each play an important role in shaping health behaviours and weight-related outcomes such as BMI, less is known about their combined association with these factors. Additionally, personality traits scores commonly follow a normal distribution, individuals with scores that deviate by one or two standard deviations (SD) above or below the mean may differ in relation to health behaviours and BMI compared to those within the average range. Exploring how high and low personality trait scores are associated with health behaviours and BMI may offer valuable insights, as individuals with high or low scores could represent high-risk subgroups with both greater support needs and a higher potential for positive change in areas such as physical activity, dietary habits, and weight management, with a particular need for tailored support to enhance adherence within these areas. The aim of the present study is to examine whether Neuroticism, Conscientiousness, including high and low scores, as well as Healthy Neuroticism and Unhealthy Neuroticism, are associated with BMI. Secondly, the study explores whether and how these associations are mediated by health behaviours, specifically physical activity, and caring about having a healthy and nutritious diet.

This cross-sectional study utilises data from the SHILD survey (Survey of Health, Impairment and Living Conditions in Denmark), which investigates current living conditions in Denmark (Kjaer et al., 2019). The survey is conducted by The National Research and Analysis Centre for Welfare. We used data from the 2016 wave of the survey (Amilon et al., 2016). By use of the personal identification number, participants were invited from a randomly selected sample of citizens aged 18–64, drawn by Statistics Denmark. The survey was sent out to 38,000 potential participants (Amilon et al., 2016) of whom 22,771 responded, corresponding to a response rate of 59.9%. Informed consent was obtained from all participants. All procedures in this research were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The present cross-sectional study was approved by the General Data Protection Regulation (p. 2024–15623).

Descriptive statistics, including means, standard deviations and frequencies were performed to understand and summarise group characteristics.

To investigate the association between personality traits and BMI, as well as the mediating role of physical activity and caring about having a healthy and nutritious diet, mediation analyses were conducted (See Figures 1, 2). Mediation analyses were conducted using Andrew F. Hayes PROCESS macro for SPSS. The models were run for each independent variable: Neuroticism, Conscientiousness, High Neuroticism, High Conscientiousness, Unhealthy Neuroticism and Healthy Neuroticism with BMI as the dependent variable. Mediators were (a) physical activity and (b) caring about having a healthy and nutritious diet. Only Neuroticism and Conscientiousness were entered into the statistical models. The remaining Big Five traits, Extraversion, Agreeableness and Openness, were excluded from the analyses. Model 4 of the PROCESS macro with 5.000 bootstrap samples, was applied for the mediation analysis. Data for Neuroticism, Conscientiousness, BMI, physical activity and caring about having a healthy and nutritious diet were analysed as continuous variables, whereas High Neuroticism, High Conscientiousness, Unhealthy Neuroticism and Healthy Neuroticism were analysed as dichotomous variables.

Prior research has indicated that associations between personality traits and BMI differ between men and women in both strength and direction (Wimmelmann et al., 2018). Thus, stratified analyses by sex were conducted. The analyses were repeated for males and females separately. Stratified analyses were conducted for educational level, as education may moderate the strength or direction of the associations. Low educational level was defined as <3 years of higher education, and high educational level, defined as ≥3 years of higher education. Similar to the non-stratified analysis, mediation analyses were subsequently performed for each of the independent variables, using BMI as outcome variable and physical activity and if the participant cared about having a healthy and nutritious diet as mediators.

To ensure that the assumptions for mediation analysis were met, data were initially examined for linearity, homoscedasticity and normality of residuals. To achieve normality in BMI, outliers were identified using the following criteria: values less than or equal to the 25th percentile (Q1) -1.5* Interquartile range (IQR) and values less than or equal to the 75th percentile (Q3) + 3 * IQR. The threshold of 3 times the IQR was chosen for the upper bound to retain BMI values up to 44.5, as using 1.5 would have excluded values above 36. Identified outlies were subsequently removed. A total of 1,137 values were identified as outliers based on BMI and removed from the dataset.

A post hoc power analysis using G*Power 3.1 (Faul et al., 2007) indicated that, with the given sample size (N = 21,619), the study was sufficiently powered (1–β > 0.99) to detect small effect sizes (f² = 0.02) in the models, using a significance level of α = 0.05.

Table 1 presents the participants characteristics including sex, age, BMI, educational level, and personality trait scores. The average age for the total sample was 43.4 years with a SD of 14.1. The average age was higher for both Unhealthy Neuroticism [mean age 45.2 years (SD 12.9)] and Healthy Neuroticism [mean age 48.5 years (SD 11.9)]. The total sample of 21,619 participants used in the mediation analysis of physical activity had an average BMI of 25.4 kg/m² (SD 4.5), this where similar across all the subgroups based on personality traits, apart from Unhealthy Neuroticism where a slightly higher BMI of 26.4 kg/m² was observed. Unhealthy Neuroticism presented with the lowest frequency of physical activity (mean 4.0 days, SD 2.1), whereas Healthy Neuroticism and Conscientiousness presented with the highest frequency of physical activity (mean 4.4 days, SD 2.1). Unhealthy Neuroticism presented with the highest mean of caring about having a healthy and nutritious diet (mean score 1.87, SD 0.7) and Healthy Neuroticism representing with the lowest mean of caring about having a healthy and nutritious diet (mean score 1.6, SD 0.6).

The total effect of Neuroticism on BMI, when Neuroticism was operationalised as a continuous variable was 0.11 (95% CI: 0.07; 0.15) in the main analysis (Table 2). When operationalised as High Neuroticism, we found the total effect for the subsample to be 0.27 (95% CI: 0.10; 0.44), (Table 2). The mediational effect of physical activity was very weak. For instance, the indirect effect of Neuroticism on BMI, through the mediator physical activity was −0.01 (95% CI: −0.01; −0.00), (Table 2). However, caring about having a healthy and nutritious diet appeared to mediate the association between Neuroticism and BMI, with an indirect effect of −0.05 (95% CI: −0.05; −0.04), as well as the association between High Neuroticism and BMI with an indirect effect of −0.11 (95% CI: −0.14; −0.08), (Table 3). Generally, the effects varied in the stratified analysis by sex and educational level, with the strata of males and low educational level showing stronger total effects of Neuroticism on BMI, and lower mediational effects of the mediators. Details can be found in Tables 2, 3.

When Conscientiousness was operationalised as a continuous variable, the total effect on BMI in the main analysis was −0.23 (95% CI: −0.27; −0.19), (Table 2). When operationalised dichotomously as High Conscientiousness, the total effect was −0.58 (95% CI: −0.71; −0.45), (Table 2). The mediational effect of both mediators was overall weak for Conscientiousness. A statistically significant mediational effect was also observed for High Conscientiousness, with the highest indirect effect present in the strata’s based on high educational level, showing an indirect effect of −0.18 (95% CI: −0.22; −0.14) for caring about having a healthy and nutritious diet and −0.10 (95% CI: −0.14; −0.08) for physical activity. Overall, the total and indirect effects varied across the different strata, with higher educational level emerging as an important factor, showing stronger associations in both total and indirect effect. Overall, we found negative total effects across all analyses for both operationalisations and both mediational models.

Healthy Neuroticism and Unhealthy Neuroticism showed opposing total effects on BMI. Unhealthy Neuroticism was consistently positively associated with BMI across all analyses, with a total effect of Unhealthy Neuroticism on BMI of 0.99 (95% CI: 0.59; 1.40) in the main analysis (Table 2). No mediation effects were found in any analyses for Unhealthy Neuroticism, except for a partial complementary indirect effect of physical activity in the higher educational level stratum 0.10 (95% CI: 0.02; 0.18), (Table 2). The total effect of Healthy Neuroticism on BMI was statistically significant only in the main analysis −0.25 (95% CI: −0.50; −0.01), (Table 2) and within the strata of higher educational level across both mediation models. However, we did find mediational effects of both mediators for Healthy Neuroticism across the majority of analyses. Physical activity fully mediated the association between Healthy Neuroticism and BMI in the main analysis, with an indirect effect of −0.05 (95% CI: −0.08; −0.02). However, the strongest indirect effect of physical activity was observed in the strata of higher educational level −0.10 (95% CI: −0.15; −0.06), although this mediation was partial. Caring about having a healthy and nutritious diet appeared to mediate the association between Healthy Neuroticism and BMI, with an indirect effect of 0.18 (95%-CI: −0.22; −0.15) in the main analysis. The strongest effect was observed in the high educational strata −0.23 (95%-CI: −0.30; −0.17), where full mediation was evident in both analyses.

The study has several notable strengths. First, it is based on a large sample, randomly selected by Statistics Denmark using national personal identification numbers. Furthermore, we examined the potential mediating roles of sex and educational level, allowing for a more nuanced understanding of how these factors may influence the associations between personality traits and BMI. However, several limitations apply for this study. First, due to the cross-sectional observational study design, causal relationships cannot be established. Second, the dietary question used was broad and nonspecific, failing to capture information about actual dietary intake. Third, the study relied on self-reported data, which poses the risk of social desirability bias, and other reporting inaccuracies, such as underreporting of body weight used to calculate BMI, and overreporting of health behaviours. Fourth, unmeasured confounding variables may explain part of the observed associations between personality traits and the outcome variables. Fifth, there is a potential for healthy volunteer bias, as individuals with more socioeconomically advantageous backgrounds are generally more likely to participate in survey-based studies. Sixth, this study focused solely on Neuroticism and Conscientiousness. While these traits show the most consistent associations with health outcomes, excluding the remaining Big Five traits may have resulted in unaccounted variance. This limits the ability to account for shared variance between the traits and may result in certain behaviours being misattributed to Neuroticism or Conscientiousness. Including all five traits in future analyses would allow for a nuanced attribution of effects. Seventh, the study used BMI as a proxy for metabolic health. Additional health indicators could have provided a more nuanced understanding of relevant associations. Eight, the generalisability of the findings is limited to a Danish context. Prior research suggests that sociocultural environments can moderate the relationship between Neuroticism and BMI, for example exposure to sociocultural environment in the United States has been shown to influence this association (Sutin et al., 2015). Indicating that the infrastructure of the society plays an imperative role and may have a shaping impact of dietary choices and physical activity habits, which limits our study’s findings to only reflect associations among the Danish population and the sociocultural norms related to the Danish society. Additionally, the associations found in this study may reflect the specific conditions of the time period in which data was collected, as national health strategies could have influenced the population. The SHILD survey was conducted in 2016, 4 years after The Danish Ministry of Health and Prevention introduced the “prevention packages” in 2012 (SST, 2013). This national initiative may have influenced population-level health behaviours and thereby introduced random variation or served as an unobserved confounding factor in the analyses.

A recent paper within the field of precision health emphasises that healthcare solutions should be tailored to the needs of diverse populations, addressing specific challenges and requirements these individuals face (Cefalu et al., 2024). Achieving this goal requires a multifaceted approach that addresses individual differences and identify those who do not benefit from the traditional healthcare strategies, particularly those who require the most attention and support. Graham et al. (2018) and Sutin et al. (2016) has earlier noted that for understanding the complexity of health related outcomes and associations with personality traits, individuals of significant interest are those who deviate markedly from the mean score (Sutin et al., 2016; Graham et al., 2018), which also might be individuals of special interest for the healthcare system. Understanding the emotional and behavioural response patterns of individuals high in Neuroticism is central to providing more effective and tailored support. Research has shown that individuals high in Neuroticism are more likely to receive healthcare advice from others, but have a counterproductive emotional and behavioural response to these advices (Tucker et al., 2006). Additionally, it has been suggested that emotional regulation difficulties is an factor in the relationship between Neuroticism and unhealthy behaviours, and that these should be addressed in interventional programmes (Singh, 2022). Such individuals may not benefit from the traditional health consultations provided by the health care system. If health interventions are tailored to the challenges that individuals high in Neuroticism meets, it may enhance adherence and facilitate optimal conditions for achieving health-related goals. For these individuals emotional and stress-related eating appears to be a significant barrier, suggesting that tailored interventions should incorporate components for emotional coping strategies and self-regulation. A higher intake of convenience foods has also been observed for individuals high in Neuroticism, underscoring the need for structured meal planning and education on simple, healthy meals. In contrast, individuals high in Conscientiousness are often more likely to adhere to health-promoting behaviours due to their long-term goal orientation. Effective support strategies for this group may involve reinforcing the long-term health benefits of sustained health behaviours and connections between daily actions and measurable health outcomes. In the current study, men with high Neuroticism, especially those with lower educational levels, were less physically active. Previous literature suggests, that men need different interventions and a different delivery of information than women for motivating them to sign up and effectively take part in the health programmes (White et al., 2011). Taken together, these findings support the importance of developing tailored health strategies for different subgroups, based on personality traits, educational level, and sex. Such strategies should acknowledge the varying health challenges, motivations, and behavioural patterns present across individuals to improve intervention reach, engagement, and effectiveness.

Emerging evidence in behavioural research highlights the potential of personality traits to enhance behaviour change by refining health interventions to the specific characteristics of the target population, which may improve behavioural changes, adherence, and improve the use of healthcare resources (Chapman et al., 2014). By aligning interventions with individuals’ specific needs, motivations, and self-regulatory tendencies, all factors shaped by personality traits, may enhance both engagement and effectiveness, as individuals are more likely to perceive the intervention as relevant and meaningful, thereby increasing the likelihood of behavioural change (Chapman et al., 2014). A recent study found that Conscientiousness and Healthy Neuroticism were associated with greater increases in daily steps during a five-week physical activity intervention period, when compared with the remaining Big Five traits (Stieger et al., 2020). These findings indicate that the efficacy of the intervention modality may depend on personality traits and trait specific preferences, which can be taken into account, in designing interventions for different sub-populations.