High blood pressure (BP) is a major risk factor for cardiovascular disease (CVD), a leading cause of mortality globally. Increasingly diagnosed in children due to rising overweight and obesity prevalence, high childhood BP can track into adulthood, potentially leading to premature atherosclerosis, type 2 diabetes, and CVD. Childhood is a critical period for establishing healthy lifestyles, with diet quality identified as a modifiable risk factor for high BP. Existing evidence on the association between childhood diet and BP is inconclusive and contradictory; some studies show higher BP with unhealthy diets, others show no association. Previous longitudinal studies have limitations, such as small sample sizes or incomplete data on dietary changes over time. This study uses a large, nationally representative longitudinal dataset (Longitudinal Study of Australian Children, LSAC) to examine the association between dietary trajectories across childhood and BP at age 10/11, considering BMI and fat mass as potential explanatory factors. The goal is to elucidate the long-term impact of consistent versus changing dietary habits on BP development during childhood and to highlight potential strategies for preventative intervention.

A 2018 systematic review identified six cross-sectional studies examining the association between dietary patterns and BP in children and adolescents. Three studies found higher BP in those consuming a "Western" diet and lower BP in those following healthy patterns. However, one study found lower hypertension prevalence with a "Modern" diet, and two showed no significant associations. Since 2018, additional cross-sectional studies have shown mixed results: some found lower diastolic or systolic BP among children with healthier diets, while others found no association. Two longitudinal studies from the Netherlands showed that higher diet quality in early childhood was associated with lower BP in later childhood, but these studies did not account for dietary changes during the follow-up period. One cohort study utilizing LSAC data, with a 53% participation rate, found a "never healthy" dietary trajectory associated with higher SBP but not DBP, after adjustment for several covariates including BMI. This study's small sample size potentially underrepresented children from disadvantaged families, who are more likely to have poor diets and at-risk cardiovascular phenotypes. This highlights the need for large, representative longitudinal studies to investigate the association between habitual dietary intake across childhood and subsequent BP. Although obesity is strongly associated with higher BP in children, the role of BMI and body composition in the association between dietary intake and BP remains unclear.

This study utilized data from the Longitudinal Study of Australian Children (LSAC), a population-based study tracking a nationally representative sample of children and their families. Data from waves 1-6 of the B-cohort and waves 1-4 of the K-cohort (ages 4/5 to 10/11 years) were analyzed. A total of 4360 children met the inclusion criteria after exclusions for missing data and specific parental characteristics (biological parents). Dietary intake was assessed at each wave using a standard set of 11 questions on food and drink consumption, with scores derived based on similarity to the Australian Dietary Guidelines (0-14 score). Group-based trajectory modeling identified distinct dietary trajectories based on these scores. Blood pressure (SBP and DBP) was measured at age 10/11 using a validated monitor. Linear regression models examined associations between dietary trajectories and BP, adjusting for relevant covariates. Models were adjusted sequentially: Model 1 included socio-demographic covariates, Model 2 added parental covariates, Model 3 added child-related covariates, Model 4 added BMI, and Model 5 added fat mass index (FMI). Interaction terms were included to test for differences in associations by sex and cohort. Statistical analyses were performed using STATA 16.0 software.

Group-based trajectory modeling revealed four dietary trajectories: "always healthy" (58.4%), "moderately healthy" (23.1%), "becoming less healthy" (14.2%), and "never healthy" (4.3%). Children in the "always healthy" trajectory had significantly lower systolic (-2.19 mmHg; 95% CI -3.78, -0.59) and diastolic BP (-1.71 mmHg; 95% CI -2.95, -0.47) compared to the "never healthy" trajectory after adjusting for socio-demographic, parental, and child-related covariates (Model 3). After further adjustment for BMI (Model 4) and FMI (Model 5), these associations were attenuated, but the association between the "always healthy" trajectory and lower diastolic BP remained significant (-1.34 mmHg; 95% CI -2.54, -0.14 after BMI adjustment, and -1.23 mmHg; 95% CI -2.43, -0.03 after FMI adjustment). The "moderately healthy" trajectory showed no significant association with SBP or DBP. There were no significant interactions by sex or cohort. Children in the "always healthy" trajectory were more likely to have mothers born overseas, with higher education, normal BMI parents, be female, non-Indigenous, breastfed for at least 6 months, and have normal BMI and physical activity.

This study's findings contribute to the limited evidence on childhood diet quality and BP. The results align with some previous studies showing higher BP among children with less healthy diets, although the effect sizes are modest (1-2 mmHg). These small differences in BP, though, are clinically relevant at a population level, as even small increases in childhood BP can contribute to cardiovascular risk in adulthood. The study's longitudinal design and adjustment for potential confounders (BMI, fat mass, and other covariates) strengthen the findings, demonstrating that healthy eating habits during childhood are associated with slightly lower BP in early adolescence, even after accounting for BMI and fat mass, particularly for diastolic BP. Importantly, the study highlights the importance of considering longitudinal dietary patterns rather than single time-point assessments. While the "always healthy" group demonstrated better BP, their diet quality was still suboptimal. This highlights the need for broader public health interventions to promote healthier eating habits in children.

This large, longitudinal study demonstrates that a consistently healthy dietary trajectory throughout childhood is associated with slightly lower diastolic blood pressure in early adolescence, even after accounting for BMI and fat mass. The modest effect size emphasizes the importance of population-level interventions aimed at improving children's dietary habits early in life to reduce long-term cardiovascular risk. Future research should focus on detailed dietary assessments, validated measures of BP in children, and exploration of other potential mediating factors to refine our understanding of these relationships.

The dietary assessment used in the LSAC, while suitable for large-scale studies, was not highly detailed and lacked formal validation. The 24-hour dietary recall may not fully capture habitual dietary intake. The blood pressure monitor used was not validated for children. A significant proportion of children were excluded due to missing data, potentially biasing the results; excluded children tended to have poorer health and health behaviors. The study did not measure mean arterial pressure (MAP), a potentially more informative indicator of cardiovascular health.