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Type: Thesis
Title: Diet and epidemiology of non-communicable chronic diseases: focusing on dietary and nutrient patterns and bone fragility in adults
Author: Melaku, Yohannes Adama
Issue Date: 2018
School/Discipline: Adelaide Medical School
Abstract: Existing evidence supports the increasing consumption of unhealthy diet and associated growing impact on the current burden of non-communicable diseases (NCDs) globally. However, evidence on the extent of diet-related NCD burden remains limited. Firstly, this thesis assesses the trends in diet-related NCDs in Australia from 1990 to 2015 and compares the results with other countries of the Organization for Economic Co-operation and Development (OECD). Fourteen dietary risk factors (eight food groups, five nutrients and fibre intake) were included in Global Burden of Disease (GBD) 2015. Body mass index, total serum cholesterol, fasting plasma glucose and systolic blood pressure were considered to mediate the relationship between dietary factors and NCDs. The results demonstrated that over the past 25 years, the burden of diet-related NCDs in Australia has declined. However, despite this and improvements in Australia’s comparative global standing, the relative contribution of dietary risk factors to NCD burden is still high in Australia. In 2015, nearly one-fifth (19.7%) of NCD deaths in Australia were attributable to dietary risk factors. Young (25–49 years) and middle-age (50–69 years) males had a higher population attributable fraction of diet-related NCD deaths and disability-adjusted life years (DALYs) than their female counterparts. Overall, more than three-quarters (80.5%) of diet-related NCD deaths were caused by cardiovascular disease (CVD) and 42.3% of all CVD deaths were attributable to dietary risks. Diets low in fruits, vegetables (FV), nuts and seeds, and whole grains, and high in sodium were the major contributors to both NCD deaths and DALYs. The findings above form the basis for the remaining studies presented in this thesis. The above study did not look at the impact of diet on musculoskeletal diseases, specifically on osteoporosis and fractures. In the subsequent studies, I hypothesize that diet is an important risk factor for osteoporosis and fractures. Previous studies on the association between dietary patterns and bone mineral density (BMD) have reported inconsistent findings. Data from the North West Adelaide Health Study (NWAHS), a population-based cohort study undertaken in Australia, are used to assess this association among adults aged 50 years and above. Overall, 1182 adults (545 males, 45.9%) had dietary data collected using a food frequency questionnaire (FFQ) and also had BMD measurements taken using Dual-energy X-ray absorptiometry (DXA). Factor analysis using the principal component analysis (PCA) method was applied to ascertain dietary patterns. Two distinct dietary patterns were identified. Pattern 1 (‘prudent’ pattern) was characterised by high intake of FV, sugar, nut-based milk, fish, legumes and high-fibre bread. In contrast, pattern 2 (‘Western’ pattern) was characterised by high levels of processed and red meat, snacks, takeaway foods, jam, beer, soft drinks, white bread, poultry, potato with fat, high-fat dairy products and eggs. Compared with the study participants with lowest consumption (first tertile) of the ‘prudent’ pattern, participants in the third tertile had a lower prevalence of low BMD (prevalence ratio (PR) = 0.52; 95% confidence interval (CI): 0.33, 0.83) after adjusting for sociodemographic, lifestyle and behavioural characteristics, chronic conditions and energy intake. Participants in the third tertile of the ‘Western’ pattern had a higher prevalence of low BMD (PR = 1.68; 95% CI: 1.02, 2.77) compared with those in tertile 1. In contrast to the ‘Western’ diet, a dietary pattern characterised by high intake of FV and dairy products is positively associated with BMD. In addition to dietary patterns, exploring the association between nutrient patterns and BMD provides further insight into the physiological mechanisms of how dietary patterns impact BMD. There is limited evidence of the link between the overall nutrients intake from diet and BMD. I assess the association between nutrient patterns and BMD among an older Australian population. Participants (n = 1135; males, 45.8%; median age, 62.0 years) with dietary and BMD data in the NWAHS were included. Dietary intake was assessed using a FFQ. BMD was measured using DXA. Nutrient patterns were identified by factor analysis. Linear regression analyses were conducted to assess the association between nutrient patterns and BMD. Multiple imputation and sensitivity analyses were conducted to investigate the effect of missing data on the estimates. Three nutrient patterns (animal-sourced [cholesterol, protein, Vitamin B12 and fat], plant-sourced [fibre, carotene, vitamin C and Lutein] and mixed-source—a combination of both animal- and plant-sourced [potassium, calcium, fibre, retinol and Vitamin B12]) were identified. After adjusting for sociodemographic, lifestyle and behavioural characteristics, chronic conditions and energy intake, animal (β = −4.07; 95% CI: −11.89, 3.76) and plant-sourced (β = −0.99; 95% CI: −7.43, 5.45) patterns were not associated with BMD. However, I found that the mixed-source pattern was positively associated with BMD (β = 10.86; 95% CI: 1.91, 19.80). There were no interactions between the pattern, other covariates and BMD. The multiple imputation and sensitivity analyses including missing data identified similar patterns of association between nutrient patterns and BMD. Whereas animal- and plant-sourced nutrient patterns are not associated with BMD, a mixed-source pattern may prevent a reduction in BMD. In addition to investigating the association of dietary and nutrient patterns with BMD, the relationship between long-term dietary and nutrient patterns and the ultimate consequence of low BMD (i.e. fracture risk) is pivotal. However, studies on long-term exposure to foods/nutrients and the associations with fracture risk are scarce. Using data from the China Health and Nutrition Survey, I determine the prospective association of dietary and nutrient patterns with fractures. Data from 15,572 adults aged ≥18 years were analysed. Fracture occurrence was self-reported and dietary intake data were collected using a 24-hour (24-h) recall method for three consecutive days, for each individual across nine waves (1989–2011). I used cumulative and overall mean, recent and baseline dietary and nutrient exposures. Hazard ratios (HR) were used to determine the associations. Two dietary (traditional and modern) and two nutrient (plant- and animal-sourced) patterns were identified. After adjusting for potential confounders, study participants within the highest intake (third tertiles) of the modern dietary and animal-sourced nutrient patterns’ cumulative scores had a 34% (HR = 1.34; 95% CI: 1.06–1.71) and 37% (HR = 1.37; 95% CI: 1.08–1.72) increase in fracture risks compared to those in the first tertiles, respectively. While the overall mean factor scores of dietary and nutrient patterns had a similar (or stronger) pattern of association as the cumulative scores, no association between recent and baseline scores and fracture was found. Greater adherence to a modern dietary and/or an animal-sourced nutrient pattern is associated with a higher total fracture risk. This suggests that a modern animal-based diet is related to bone fragility. A repeated three-day 24-h recall dietary assessment provides a stronger association with fracture compared to a recent or baseline exposure. In the above studies, I used factor analysis with PCA method. However, in addition to this method, there are other common data reduction methods. The relative advantages of these methods, particularly in identifying dietary patterns associated with bone mass, have not been investigated. I evaluated three methods: PCA, partial least-squares (PLS) and reduced-rank regressions (RRR) in determining dietary patterns associated with bone mass. Dietary patterns were constructed using PCA, PLS and RRR and compared based on the performance to identify plausible patterns associated with BMD and bone mineral content (BMC). PCA, PLS and RRR identified two, four and four dietary patterns, respectively. All methods identified similar patterns for the first two factors (factor 1, ‘prudent’ and factor 2, ‘Western’ patterns). Three, one and none of the patterns derived by RRR, PLS and PCA were significantly associated with bone mass, respectively. The ‘prudent’ and dairy (factor 3) patterns determined by RRR were positively and significantly associated with BMD and BMC. Vegetables and fruit pattern (factor 4) of PLS and RRR was negatively and significantly associated with BMD and BMC, respectively. RRR was found to be more appropriate in identifying more (plausible) dietary patterns that are associated with bone mass than PCA and PLS. Nevertheless, the advantage of RRR over the other two methods (PCA and PLS) should be confirmed in future studies. The findings from these studies indicate that diet is a leading risk factor for the current burden of disease in Australia and has a significant impact on bone health among adults in Australia and China. In identifying dietary patterns that are associated with bone health, dietary data collection and analysis methods are important factors that potentially bias findings. These analyses have not previously been undertaken and indicate the potential implications of diet on long-term bone health. The findings have significant implications in public health interventions and clinical practices. Future studies should focus on the potential mechanisms and pathways of the associations of diet with osteoporosis and fracture risks. Identification of mediating factors and investigating their roles in the pathways should be the focus of future studies. Further evaluation of statistical methods in the analysis of dietary patterns associated with bone health and other disease outcome is warranted.
Advisor: Shi, Zumin
Gill, Tiffany
Adams, Robert
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 2018
Keywords: Diet
dietary pattern
nutrient pattern
non-communicable diseases
burden of disease
bone mass
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