Combined associations of diet quality, physical activity, and their changes over time with cardiometabolic risk and mortality
Physical activity (PA) and diet quality have each been shown to be inversely associated with cardiometabolic diseases (CMD), their risk factors, and mortality. However, their combined impact on health outcomes has been less explored, particularly when considering their changes over time. To draw public health messages that can be widely applicable, it is essential to capture long-term dynamic patterns of health behaviours, exploring their possible synergistic, cumulative, or compensatory impacts on various outcomes. The overall aim of my PhD is to evaluate the associations of combined trajectories of diet quality and PA with cardiometabolic risk and longevity. In the first project of my PhD, I systematically reviewed the evidence from prospective observational cohorts on the associations of changes over time in diet quality, PA and combined heath behaviours with cardiometabolic risk and mortality of adults. 17,311 titles were screened and 139 were included in the final synthesis. I developed two meta-analytical methods that allowed pooling of findings. In the first method, I used a dose assignment approach to generate a single effect estimate per study. The analysis demonstrated that increases in PA and diet quality over time were associated with significant risk reductions in a composite outcome of any cardiometabolic diseases - including, but not limited to, cardiovascular disease (CVD) and type 2 diabetes mellitus (T2DM) - and mortality. Specifically, for PA, the relative risk reduction was 12% (95% CI: 10–14%) and for diet quality was 6% (95% CI: 3–10%). The second method allowed identification of different trajectories of health behaviours over time and for the same composite outcome, revealed the greatest risk reduction for the “high–high” trajectory (39% [95% CI: 44–33%] for PA and 30% [95% CI: 26–35%] for diet quality). In the second project of my PhD, combined associations of diet quality, PA, and their trajectories with all-cause mortality, cause-specific mortality, and incidence of diabetes mellitus (DM) and CVD were evaluated, using data from the EPIC-Norfolk study with nearly three decades of follow-up. With repeated measurement of health behaviours among 9,349 participants, Mediterranean diet score (MDS) and physical activity energy expenditure (PAEE) were derived. Both baseline status of health behaviours and how they changed over time (ΔPAEE and ΔMDS) were significantly and inversely associated with all outcomes (hazard ratios [HRs] ranging from 0.89 to 0.96 per SD increase in exposures). Combined trajectory analysis revealed that increase over time in PAEE and MDS in combination was associated with the lowest mortality and cardiometabolic risk. Evidence of synergism in reducing the incidence of CVD was observed when diet quality and PA were combined. At the population level, consistent favourable levels of PA and diet quality could prevent 9% of premature death and reduce cumulative incidence of DM by 22% and CVD by 16%. The greatest benefit arose when an active lifestyle was combined with a high-quality diet, initiated earlier in adulthood, and maintained over time. In the third project of my PhD, concurrent changes in diet quality and objectively measured PA and their relation to changes in adiposity and cardiometabolic risk factors were assessed, using data from the Fenland Study among 7,256 participants. For markers of adiposity, I used data on changes in weight and body mass index as well as changes in body composition (body fat distribution), assessed using dual-energy X-ray absorptiometry and abdominal ultrasound. With repeat assessments approximately 7 years apart, increases in ΔMDS and ΔPAEE were independently and jointly associated with improvements in adiposity markers. The greatest obesity-related benefits were achieved by combining diet quality and physical activity (for instance, compared to participants with relatively stable MDS and PAEE, increase over time in both was associated with 1.86 [1.44 to 2.28] kg lower body fat mass). Overall, similar inverse associations were observed for a range of cardiometabolic risk factors (indices of glycaemia, blood pressure and lipids), with evidence of synergism for reduction of blood pressure. In summary, the key finding of my PhD research is that optimised levels of diet quality (e.g., moderate or greater adherence to a Mediterranean-type diet) and activity (e.g., moderate-intensity PA of 150 minutes or more per week) in any stage of adulthood can yield cardiometabolic benefits over the long term. Importantly, even late in life adoption of these behaviours is still relevant for health. The negative consequences of a poor diet cannot be fully counterbalanced through PA, nor a high-quality diet completely offset the risks of a sedentary lifestyle, therefore, these health behaviours should be viewed as complementary rather than competing strategies for improving health. If anything, when combined, they appear to have a synergistic beneficial association for some cardiometabolic risk factors, related diseases and longevity.
Adiposity, Cardiometabolic Disease, Cardiometabolic Risk, Cardiovascular Disease, Cohort Study, Diabetes Mellitus, Energy Expenditure, Epidemiology, Mediterranean Diet, Mortality, Nutritional Epidemiology, Physical Activity
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