Person: Lu, Yuan
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Publication Impact of Multiple Risk Factors and Preventive Interventions on Cardiovascular Diseases and Disparities(2015-01-16) Lu, Yuan; Ezzati, MajidMajor cardiovascular risk factors have changed over the past 3-4 decades throughout the world. While adiposity and diabetes are rising worldwide, blood pressure and cholesterol are declining in high-income and even some middle-income countries, possibly due to improvements in diet or better diagnosis and treatment; the same risk factors have remained unchanged or even increased in low-income countries. To formulate effective prevention and health system policies, there is need to understand the implications of these diverse trends for cardiovascular diseases (CVDs). This dissertation focuses on quantifying the impact of multiple risk factors and preventive interventions on CVDs and their disparities at the population level. Answering this question requires information on how much of the effects of adiposity on CVDs are mediated through other metabolic risk factors (i.e. high blood pressure, high serum cholesterol and high blood glucose), which themselves have other determinants. The first paper quantifies the direct as well as the mediated effects of excess weight on coronary heart disease (CHD) and stroke through blood pressure, serum cholesterol and blood glucose. The analyses use data of 97 prospective cohorts with more than 1.8 million participants. This allows for assessing whether the extent of mediation is modified by geographical region, study period, and other characteristics of study populations. The second paper revisits the above question using causal inference models and further quantifies the role of inflammatory markers as potential mediators. The analyses use individual-level data from 9 prospective cohort studies that have high-quality measurements of metabolic and inflammatory biomarkers. The third paper uses national data sources in the United States (US) and estimates the distributions of 10-year risk of fatal CHD by race. It also assesses the effects of different population-wide and targeted interventions on CHD risk distributions and their disparities between blacks and whites. Our findings suggest that nearly half of excess risk for CHD and three-quarters of excess risk for stroke due to excess weight were mediated through three metabolic risk factors: blood pressure, cholesterol, and glucose. Inflammatory biomarkers had much smaller roles than the combination of metabolic risk factors. In the US, the distribution of 10-year CHD risk was shifted to the right among blacks compared to whites and had a heavier tail, leading to a substantially larger proportion of blacks in the high-risk group. A risk-based intervention that identifies and treats these individuals could substantially reduce both the overall risk of CHD and its racial disparities. These results together provide the quantitative evidence on the impact of cardiovascular risk factors and selected interventions on CVDs and their disparities.Publication Trends and mortality effects of vitamin A deficiency in children in 138 low-income and middle-income countries between 1991 and 2013: a pooled analysis of population-based surveys(Elsevier BV, 2015) Stevens, Gretchen A; Bennett, James E; Hennocq, Quentin; Lu, Yuan; De-Regil, Luz Maria; Rogers, Lisa; Danaei, Goodarz; Li, Guangquan; White, Richard A; Flaxman, Seth R; Oehrle, Sean-Patrick; Finucane, Mariel M; Guerrero, Ramiro; Bhutta, Zulfiqar A; Then-Paulino, Amarilis; Fawzi, Wafaie; Black, Robert E; Ezzati, MajidBACKGROUND: Vitamin A deficiency is a risk factor for blindness and for mortality from measles and diarrhoea in children aged 6-59 months. We aimed to estimate trends in the prevalence of vitamin A deficiency between 1991 and 2013 and its mortality burden in low-income and middle-income countries. METHODS: We collated 134 population-representative data sources from 83 countries with measured serum retinol concentration data. We used a Bayesian hierarchical model to estimate the prevalence of vitamin A deficiency, defined as a serum retinol concentration lower than 0·70 μmol/L. We estimated the relative risks (RRs) for the effects of vitamin A deficiency on mortality from measles and diarrhoea by pooling effect sizes from randomised trials of vitamin A supplementation. We used information about prevalences of deficiency, RRs, and number of cause-specific child deaths to estimate deaths attributable to vitamin A deficiency. All analyses included a systematic quantification of uncertainty. FINDINGS: In 1991, 39% (95% credible interval 27-52) of children aged 6-59 months in low-income and middle-income countries were vitamin A deficient. In 2013, the prevalence of deficiency was 29% (17-42; posterior probability [PP] of being a true decline=0·81). Vitamin A deficiency significantly declined in east and southeast Asia and Oceania from 42% (19-70) to 6% (1-16; PP>0·99); a decline in Latin America and the Caribbean from 21% (11-33) to 11% (4-23; PP=0·89) also occurred. In 2013, the prevalence of deficiency was highest in sub-Saharan Africa (48%; 25-75) and south Asia (44%; 13-79). 94 500 (54 200-146 800) deaths from diarrhoea and 11 200 (4300-20 500) deaths from measles were attributable to vitamin A deficiency in 2013, which accounted for 1·7% (1·0-2·6) of all deaths in children younger than 5 years in low-income and middle-income countries. More than 95% of these deaths occurred in sub-Saharan Africa and south Asia. INTERPRETATION: Vitamin A deficiency remains prevalent in south Asia and sub-Saharan Africa. Deaths attributable to this deficiency have decreased over time worldwide, and have been almost eliminated in regions other than south Asia and sub-Saharan Africa. This new evidence for both prevalence and absolute burden of vitamin A deficiency should be used to reconsider, and possibly revise, the list of priority countries for high-dose vitamin A supplementation such that a country's priority status takes into account both the prevalence of deficiency and the expected mortality benefits of supplementation.Publication National, regional, and global trends in adult overweight and obesity prevalences(BioMed Central, 2012) Stevens, Gretchen A; Singh, Gitanjali; Lu, Yuan; Danaei, Goodarz; Lin, John K; Finucane, Mariel M; Bahalim, Adil N; McIntire, Russell K; Gutierrez, Hialy R; Cowan, Melanie; Paciorek, Christopher J; Farzadfar, Farshad; Riley, Leanne; Ezzati, MajidBackground: Overweight and obesity prevalence are commonly used for public and policy communication of the extent of the obesity epidemic, yet comparable estimates of trends in overweight and obesity prevalence by country are not available. Methods: We estimated trends between 1980 and 2008 in overweight and obesity prevalence and their uncertainty for adults 20 years of age and older in 199 countries and territories. Data were from a previous study, which used a Bayesian hierarchical model to estimate mean body mass index (BMI) based on published and unpublished health examination surveys and epidemiologic studies. Here, we used the estimated mean BMIs in a regression model to predict overweight and obesity prevalence by age, country, year, and sex. The uncertainty of the estimates included both those of the Bayesian hierarchical model and the uncertainty due to cross-walking from mean BMI to overweight and obesity prevalence. Results: The global age-standardized prevalence of obesity nearly doubled from 6.4% (95% uncertainty interval 5.7-7.2%) in 1980 to 12.0% (11.5-12.5%) in 2008. Half of this rise occurred in the 20 years between 1980 and 2000, and half occurred in the 8 years between 2000 and 2008. The age-standardized prevalence of overweight increased from 24.6% (22.7-26.7%) to 34.4% (33.2-35.5%) during the same 28-year period. In 2008, female obesity prevalence ranged from 1.4% (0.7-2.2%) in Bangladesh and 1.5% (0.9-2.4%) in Madagascar to 70.4% (61.9-78.9%) in Tonga and 74.8% (66.7-82.1%) in Nauru. Male obesity was below 1% in Bangladesh, Democratic Republic of the Congo, and Ethiopia, and was highest in Cook Islands (60.1%, 52.6-67.6%) and Nauru (67.9%, 60.5-75.0%). Conclusions: Globally, the prevalence of overweight and obesity has increased since 1980, and the increase has accelerated. Although obesity increased in most countries, levels and trends varied substantially. These data on trends in overweight and obesity may be used to set targets for obesity prevalence as requested at the United Nations high-level meeting on Prevention and Control of NCDs.