Liang Wang, MD, DrPH,MPH, FACE, FTOS

Director of Epidemiology, Associate Professor, Public Health

Background

Dr. Liang Wang is Director and tenured Associate Professor of Epidemiology at Baylor University, Texas, USA. He is an elected Fellow of the American College of Epidemiology and Fellow of The Obesity Society. He has been a Visiting Scientist in the department of nutrition at Harvard T. H. Chan School of Public Health and a Visiting Scholar at UNC Chapel Hill Gillings School of Global Public Health. His research focuses on obesity, nutrition epidemiology, health education and promotion, etc. Dr. Wang has published more than 140 peer-reviewed papers (e.g., International Journal of Epidemiology, The American Journal of Clinical Nutrition, Nutrients, The Journal of the American College of Cardiology, European Heart Journal, Diabetologia, Obesity Reviews, Advances in Nutrition), book chapters (e.g., International Encyclopedia of Public Health, China Blue Book on Obesity Prevention and Control). He has been a PI and Co-I on multiple grants (e.g., NIH, PCORI). He is Associate Editor of Nutritional Journal and BMC CERA, and Guest Editor and Topic Editor of Nutrients; as well as the editorial board member and reviewer for over 30 international journals. Dr. Wang has been serving as President of China Health Policy and Management Society (CHPAMS; www.chpams.org), Associate Director of China-Tennessee Health Education Training Institute, Chair of Public Relations of North America Chinese Society for Nutrition (NACSN), Founding President of the International Chinese Nutrition Young Scholar Network (ICNYSN; www.icnysn.org), Founding President of Institute of Health Education and Lifecourse Promotion (iHELP). He has been awarded NACSN Outstanding Leadership and Service Award in 2016, ETSU College of Public Health (COPH) Dean’s Special Recognition Award for University Leadership Faculty Senate in 2017, ETSU COPH Dean’s Special Recognition Award for Service on the Faculty Council in 2017, and ETSU COPH College Foundation Service Award in 2018. 
 

Research interests

Obesity, nutrition epidemiology, health education and promotion, global health

Selected research grants (funded)

Exploration on the application of new telemedicine technology for pregnancy care in underdeveloped areas of China and its role in improving the competencies of primary care providers: A polit study in Guangdong Province (1/1/2022-12/31/2023)

• Serving as Co-PI for $80,000 China Medical Board (USA) project (Funded).

Family context, child characteristics, child-rearing features, and obesity risks: a 15-year longitudinal analysis

• Serving as PI for $148K NIH R03 project

Developing a Research Agenda to Prevent and Control CVD in Central Appalachia

• Coinvestigated funded PCORI project valued at $250K  

Childhood obesity prevention programs and related policies in China and comparison with other countries

• Coinvestigating $30K UNICEF project  

Multilevel systems-oriented childhood obesity study in China

• Principally investigated subcontract of SUNY Buffalo for U54 Center P3 Grant for NIH/NICHD (U54HD070725-01) project

Population health improvement plan

• Coinvestigated funded $20K Tennessee Department of Health project

Influence of healthcare setting on obesity risk among U.S. children

• Served as PI for $8K+ funded project with ETSU Research Development Committee Major Grant

College students as facilitators to reduce adolescent obesity disparity

• Coinvestigated $970K+ project funded by NIH (R01)/Center on Minority Health and Health Disparities

Selected publications (from >140 publications)

1. Wang Y, Ding M, Li Y, Wang L, Rich-Edwards J, Florio A, Manson J, Chavarro J. Breastfeeding duration and subsequent risk of mortality among US women: a prospective cohort study. eClinicalMedicine (in press)
2. Wang L, Morelen D, Alamian A. Association between key family and individual factors and the risk of obesity in offspring: findings from a prospective cohort study. Scientific Reports. 2022; 12:15666.
3. Gao L, Zhu J, Wang L, Wen L, Chen Z, Zhao B, Wang W, Wang Y. Interactions between self-perceived weight status and lifestyle behaviors and their associations with childhood obesity: results from the Childhood Obesity Study in China Mega-Cities. International Journal of Environmental Research and Public Health. 2022;19(16):9921.
4. Wang YX, Ding M, Li Y, Wang L, Rich-Edwards J, Florio A, Manson J, Chavarro J. Birth weight and long-term risk of mortality among US men and women: results from three prospective cohort studies. The Lancet Regional Health – Americas. 2022;15:100344.
5. Chen X, Jiang Y, Wang Z, Chen Y, Tang S, Wang S, Su L, Huang X, Long D, Wang L, Guo W, Zhang Y. Alteration in gut microbiota associated with Zinc deficiency in school-age children. Nutrients. 2022; 14(14):2895.
6. Gong S, Wang L, Zhou Z, Wang K, Alamian A. Income disparities in obesity trends among U.S. adults: An analysis of the 2011-2014 California Health Interview Survey. International Journal of Environmental Research and Public Health. 2022;19(12):7188.
7. Li T, Xie Y, Wang L, Huang G, Cheng Y, Hou D, Liu W, Zhang T, Liu J. The association between lead exposure and bone mineral density in childhood and adolescence: results from NIHANES 1999-2006 and 2011-2018. Nutrients. 2022, 14, 1523.
8. Yin J, Huang Y, Liu G, Wang L, Shan Z, Liu L. Trends in dietary macronutrient composition and diet quality among U.S. adults with diagnosed and undiagnosed elevated glycemic status: a serial cross-sectional study. American Journal of Clinical Nutrition. 2022;nqac061.
9. Wei J, Wang L, Kulshreshtha A, Xu H. Adherence to life’s simple 7 and cognitive function among older adults: the National Health and Nutrition Examination Survey 2011-2014. Journal of the American Heart Association. 2022;0:e022959
10. Wang YX, Farland L, Wang S, Gaskins A, Wang L, Rich-Edwards J, Tamimi R, Missmer S, Chavarro J. Association of infertility with premature mortality among US women: a prospective cohort study. The Lancet Regional Health- Americas. 2021,100122,ISSN 2667-193X.
11. Wang Z, Chen Y, Tang S, Chen S, Gong S, Jiang X, Wang L^*, Zhang Y^*. Dietary diversity and nutrient intake of Han and Dongxiang smallholder farmers in poverty area of Northwest China. Nutrients. 2021; 13(11):3908. (^#Corresponding author).
12. Wang YX, Minguez-Alarcon L, Gaskins A, Wang L, Ding M, Missmer S, Rich-Edwards J, Manson J, Chavarro J. Pregnancy loss and risk of cardiovascular disease: the Nurses’ Health Study II. European Heart Journal, 2021;ehab737, 
13. Wang YX, Wang SW, Mitsunam M, Pan A, Manson JE, Rich-Edwards JW, Wang L, Zhang CL, Chavarro JE. Pre-pregnancy menstrual cycle regularity and length and the risk of gestational diabetes mellitus: prospective cohort study. Diabetologia, 2021;64(11):2415-2424.
14. Kadam I, Neupane S, Wei J, Fullington LA, Li T, An R, Zhao L, Ellithorpe A, Jiang X*, Wang L*. A systematic review of diet quality index and obesity among Chinese adults. Nutrients. 2021; 13(10):3555 (*Corresponding author).
15. Zhu B, Wu Y, Cai Z, Liao C, Sun L, Liu Z, Chen H, Huang X, Lin Q, Zhou X, Wang L, Zhang M, Yang B. A prospective epidemiological analysis of controlling nutritional status score with the poor functional outcomes in Chinese patients with hemorrhagic stroke. British Journal of Nutrition. 2021;1-18.
16. Sun Y, Chen C, Mustieles V, Wang L, Zhang Y, Wang Y, Messerlian C. Association of blood trihalomethane concentrations with risk of all-cause and cause-specific mortality in U.S. adults: a prospective cohort study. Environmental Science & Technology. 2021;55:9043-9051.
17. Nie P, Ding L, Sousa-Poza, Leon A, Xue H, Jia P, Wang L, Wang Y. Inequality of weight status in urban Cuba: 2001-2010.  Population Health Metrics. 2021;19(1):24.
18. Wang YX, Arvizu M, Rich-Edwards JW, Wang L, Rosner B, Stuart JJ, Rexrode KM, Chavarro JE. Hypertensive disorders of pregnancy and subsequent risk of premature mortality. Journal of the American College of Cardiology, 2021;77(10): 1302–1312.
19. Wu Y, Wang L, Zhu J, Gao L, Wang Y. Growing fast food consumption and obesity in Asia: challenges and implications. Social Science & Medicine. 2021; 269:113601.
20. Wang L, Lee Y, Wu Y, Zhang X, Jin C, Huang Z, et al. Prospective study of waist circumference trajectories and incident cardiovascular disease. The American Journal of Clinical Nutrition. 2021;113(2):338-347.
21. Wang L, Wang H, Zhang B, Popkins BM, Du S. Trends in fat intake and their impacts on body weight and the risk of overweight and obesity among Chinese adults. Nutrients. 2020,12,3272.
22. Wang L, Liu X, Liu Z, Jia C. Digital media use and subsequent self-harm during a 1-year follow-up of Chinese adolescents. Journal of Affective Disorders. 2020; 277:279-286.
23. Omoike O*, Pack R, Mamudu H, Liu Y, Strasser S, Zheng S, Okoro J, Wang L*. Association between per and polyfluoroalkyl substances and markers of inflammation and oxidative stress. Environmental Research. 2020;110361. (*Corresponding author)
24. Omoike O*, Pack R, Mamudu H, Liu Y, Wang L*. A cross-sectional study of the association between perfluorinated chemical exposure and cancers related to deregulation of estrogen receptors. Environmental Research. 2020;110329. (*Corresponding author)
25. Omoike O, Wang L, Oke A, Johnson K. Predicting bone turnover following tobacco exposure using bone alkaline phosphatase and N-telopeptide biomarkers and possible variability and effect modification of these markers by race/ethnicity. Biomarkers. 2020;25(5):410-416.
26. Nie P, Ding LL, Sousa-Poza A, Leon AA, Xue H, Jia P, Wang L, Wang Y. Socioeconomic position and the health gradient in urban Cuba: Dimensions and mechanisms. BMC Public Health. 2020;20(1):866.
27. Gao L, Bhurtyal A, Wei J, Akhtar P, Wang L, Wang Y, etc. Double burden of malnutrition and nutrition transition in Asia: a case study of four selected countries with different socioeconomic development. Advances in Nutrition. 2020;nmaa064.
28. Wei J, Bhurtyal A, Dhungana R, Bhattarai B, Zheng J, Wang L, Sun XM, Maskey M, Wang Y. Changes in patterns of the double burden of under- and over-nutrition in Nepal over time. Obesity Reviews. 2019; 20(9):1321-1334.
29. An R, Xue H, Wang L, Wang Y. Projecting the impact of a nationwide school plain water access intervention on childhood obesity: a cost-benefit analysis. Pediatric Obesity. 2018; 13(11):715-723.
30. Yang B, Ren XL, Wang ZY, Wang L, Zhao F, Guo XJ, Li D. Biomarker of long-chain n-3 fatty acid intake and breast cancer: Accumulative evidence from an updated meta-analysis of epidemiological studies. Critical Reviews in Food Science Nutrition. 2018:1-13.
31. Wang Y, Wang L, Qu W. New national data show alarming increase in obesity and noncommunicable chronic diseases in China. European Journal of Clinic Nutrition. 2017; 71(1):149-150.
32. Liu Y, Sayam S, Shao X, Wang K, Sheng S, Lu Y, Wang L. Prevalence of and trends in diabetes among veterans in the United States, 2005-2014. Preventing Chronic Disease. 2017; 14:E135.
33. Zhao Y, Wang L*, Wang H, Wang Y. Fast food consumption and its associations with obesity and hypertension among children: results from the baseline data of the Childhood Obesity Study in China Mega-cities. BMC Public Health.  2017; 17(1):933. (*co-first author)
34. Zhao Y, Wang L*, Xue B, Wang Y. Associations between general and central obesity and hypertension among children: The Childhood Obesity Study in China Mega-Cities. Scientific Reports. 2017; 7(1):16895. (*co-first author)
35. Yan Y, Liu J, Wang L, Hou D, Zhao X, Chen H, Mi J. Independent influences of excessive body weight and elevated blood pressure from childhood on left ventricular geometric remodeling in adulthood. International Journal of Cardiology. 2017; 243: 492-496.
36. Liu J,* Wang L,* Sun J, Liu G, Yan W, Xi B, Xiong F, Ding W, Huang G, Mi J. Bone mineral density reference standards for Chinese children aged 3-18: cross-sectional results of the 2013-2015 China Child and Adolescent Cardiovascular Health (CCACH) Study. (*Co-first author). BMJ Open. 2017; 7(5):e014542.
37. Wang L, Southerland J, Wang K, Bailey B, Alamian A, Stevens M, Wang Y. Ethnic differences in risk factors for obesity among adults in California, the United States. Journal of Obesity. vol. 2017, Article ID 2427483, 10 pages, 2017. doi:10.1155/2017/2427483
38. Wang L, Collins C, Pitts M, Xie B, Wang Y. Breastfeeding reduces childhood obesity risks. Childhood Obesity 2017; 13(3):197-204.
39. Wang Y*, Wang L*, Xue H, Qu W. A review of the growth of the fast food industry in China and its potential impact on obesity. International Journal of Environmental Research and Public Health. 2016, 13(11), pii: E1112 (*co-first author).
40. Tian X, Di Z, Yu L, Ren X, Chai Y, Ding F, Chen J, Southerland J, Cui Z, Hu X, Xu J, Xu S, Qian G, Wang L*. A study on the development of an infectious disease specific health literacy scale. BMJ Open. 2016;6:e012039 (*Corresponding author)
41. Leinaar E, Alamian A, Wang L. A Systematic review of the relationship between asthma, obesity, and the effects of physical activity in youth. Annals of Epidemiology. 2016; 26(7):504-510.e6.
42. Mamudu H, Paul T, Wang L, Veeranki SP, Panchal HB, Alamian A, Sarnosky K, Budoff M. The effects of multiple coronary artery disease risk factors on subclinical atherosclerosis in a rural population in the United States. Preventive Medicine. 2016; 88:140-146.
43. Wang L, Wang K, Liu X, He Y. Association of education and lifestyle factors with the perception of genetic knowledge on the development of lung cancer. Indian Journal of Medical Research. 2016; 143 (Supplement): 120-125.
44. Tian X, Zhao G, Cao D, Wang D, Wang L*. Health education and promotion at the site of an emergency: experience from the Chinese Wenchuan earthquake response. Global Health Promotion 2016; 23(1):15-26 (*Corresponding author).
45. Wang L, Cui L, Wang Y, Vaidya A, Chen S, Zhang C, Zhu Y, Li D, Hu FB, Wu S, Gao X. Resting heart rate and the risk of developing impaired fasting glucose and diabetes: The Kailuan prospective study. International Journal of Epidemiology. 2015; 44(2):689-699.
46. Wang L, Wang K, Gao X, Paul T, Cai J, Wang Y. Sex difference in the association between obesity and asthma in U.S. adults: Findings from a national study. Respiratory Medicine. 2015; 109(8):955-962.
47. Liang Y, Hou D, Zhao X, Wang L, Hu Y, Liu J, et al. Childhood obesity affects adult metabolic syndrome and diabetes. Endocrine. 2015; 50(1):87-92.
48. Wang XS, Guo HJ, Wang L*, Li XN, Huang MH, Liu ZH, Liu XF, Wang KS, Alamian A, Anderson JL. Investigation of residents' health literacy status and its risk factors in Jiangsu Province in China. Asia-Pacific Journal of Public Health 2015; 27(2): NP2764-72. (*Corresponding author)
49. Wang L, Slawson DL, Relyea G, Southerland J, Wang Y. Prevalence of and risk factors for adolescent obesity in southern Appalachia, 2012. Preventing Chronic Disease. 2014; 11: E222.
50. Liang Y, Hou D, Shan X, Zhao X, Hu Y, Jiang B, Wang L, et al. Cardiovascular remodeling relates to elevated childhood blood pressure: Beijing Blood Pressure Cohort Study. International Journal of Cardiology. 2014; 177(3):836-839.
51. Wang L, Mamudu HM, Alamian A, Anderson JL, Brook B. Independent and joint effects of prenatal maternal smoking and maternal exposure to secondhand smoke on the development of adolescent obesity: A longitudinal study. Journal of Paediatrics and Child Health. 2014; 50(11):908-915.
52. Wei X, Wang L*, Dong J, Zhang M, Anderson JL. Evaluation of health advisory service for H7N9 control in China. Annals of Epidemiology. 2013; 23(11):724-5. (*Corresponding author)
53. Wang L, Liu XF, Luo XG, Zeng M, Zuo LJ, Wang K. Genetic variants in the fat mass- and obesity- associated (FTO) gene are associated with alcohol dependence. Journal of Molecular Neuroscience. 2013; 51(2):416-424.
54. Wang L, Alamian A, Southerland J, Wang K, Anderson JL, Stevens M. Cesarean section and the risk of overweight in grade 6 children. European Journal of Pediatrics. 2013; 172(10):1341-1347.
55. Wang L, Dalton WT, Schetzina KE, Fulton-Robinson H, Holt N, Ho Ai-leng, Tudiver F, Wu TJ. Modeling aspects of home food environment with dietary intake and body mass index among overweight and obese children in southern Appalachia. Southern Medical Journal. 2013; 106(10):550-557.
56. Wang L, Wang KS. Age Differences in the Associations of Behavioral and Psychosocial Factors with Stroke. Neuroepidemiology. 2013; 41(2): 94-100.
57. Wang L, Anderson JL, Dalton WT, Wu TJ, Liu CX, Zheng SM, Liu XF. Maternal depressive symptoms and the risk of overweight in their children. Maternal and Child Health Journal. 2013; 17(5):940-948.
58. Wang L, Mamudu HM, Wu TJ. The Impact of maternal prenatal smoking on the development of childhood overweight in school-aged children. Pediatric Obesity. 2013; 8(3):178-188.
59. Wang L, Wu TJ, Liu XF, Anderson JL, Alamian A, Fu MS, Li J. Pesticide exposure during pregnancy and low birth weight. WHO South-SEAJPH. 2012; 1(3):232-238.
60. Wang L, Wu T, Anderson J, Florence L. Prevalence and risk factors of maternal depression during the first three years of child-rearing. Journal of Women’s Health (Larchmt). 2011; 20: 711-718.

 

BOOK CHAPTERS, MONOGRAPHS, AND MANUALS

1. Tian X, Wang L. Co-Principal Editor. A Collection of Exemplary Health Education and Promotion Cases in China. Chinese Center for Health Education. People’s Medical Publishing House Co., LTD, 2019.
2. Wang Y, Sun M, Wang L. et al. Chapter 3: Obesity Screening and Diagnosis. “Prevention and Control of Obesity in China”. Chinese Nutrition Society (CNS). People’s Medical Publishing House Co., LTD, 2019.
3. Wang Y, Wang L. Child Obesity and Health. International Encyclopedia of Public Health, 2nd Edition. Expected Release: Nov 1, 2016. Print Book ISBN: 9780128036785. Elsevier Publisher.
4. Wang K, Wang L. Molecular Aspects of Alcohol and Nutrition, First Edition edited by V Patel. Nov 1, 2015. Print Book ISBN: 9780128007730. Elsevier Publisher.

 

Selected published abstracts

1. Wang L, Du S, Wang H, Popkin BM. Influence of dietary fat intake on bodyweight and risk of obesity among Chinese adults, 1991–2015: a prospective cohort study. The Lancet. 2018.392;S20.
2. Alamian A, Wang L, Pitts M, Ikekwere J, Hall A. Infant sleep problems increase the odds of childhood overweight at grade 6: differential effects of commonly used definitions of sleep problems. Circulation. 2014;129(Suppl 1):AP106.
3. Southerland J, Wang L, Dalton W, Slawson D. Weight misperception and health-related quality of life in Appalachian adolescents. Circulation. 2014;129(Suppl 1):AP287.
4. Wang L, Alamian A, Southerland J, Wang KS, Anderson JL, Stevens M. Cesarean section associated with increased risk for overweight and obesity in grade six children. Circulation. 2013: 127: AP289.
5. Wang L, Mamudu HM, Anderson JM, Alamian A. Maternal smoking during pregnancy and the risk of adolescent obesity. American Journal of Epidemiology. 2012;175(Suppl 11):1-145.

Associate Editor: Nutrition Journal (impact factor: 4.334)

Guest Editor: Nutrients (impact factor: 6.706), Special Issue on “Nutritional Epidemiology among Chinese population”. Please submit via

https://www.mdpi.com/journal/nutrients/topical_collections/Nutritional_Epidemiology_among_Chinese_Populations

Guest Editor: Frontiers in Health Economics, Special Issue on “Asian National Health Sectors Growth in the Next Decade - Optimism despite Challenges Ahead”

 

Selected reviewer experiences

Nature Communications, JAMA Pediatrics, Internal Journal of Epidemiology, Journal of Epidemiology and Community Health, Maternal and Child Health Journal, Obesity Reviews, Obesity, Pediatric Obesity, Childhood Obesity, International Journal of Obesity, Advances in Nutrition, Maternal and Child Nutrition, Journal of Epidemiology and Community Health, Pediatric and Perinatal Epidemiology, International Journal of Public Health

 

HONORS AND REWARDS

• 2022-2024, President, China Health Policy and Management Society (www.chpams.org), USA
• Founding Chair, U.S.-China Health Dean’s Forum, March 25-26, Baylor University, USA. https://mp.weixin.qq.com/s/cK7-GnqXxeGXodwIA8Nsdw
• Cochair, Clinical Epidemiology scientific program, 17^th Congress of Asian Society for Pediatric Research (ASPR), September 17-18, 2022  https://www.sciconf.cn/m/lives/details/10671?lang=cn&c_date=2022-09-18&state=1664561428&openid=oXzmFjmHuPscdhtSnzkbt1IfILAQ
• Judge, Baylor Global Health Week Case Competition, 2022
• Cochair, the Joint NACAN and ICNYSN Scientific Symposium in 2021 (The 2^nd Annual NACAN Summit (2021): Frontiers in Nutrition), https://mp.weixin.qq.com/s/mPZ3fOS_QUTWNBu2CmCQEA
• Cochair, Clinical Epidemiology scientific program, 16^th Congress of Asian Society for Pediatric Research (ASPR), September 11-12, 2021 https://mm.sciconf.cn/en/web/speaker-detail/1695?user_id=3656708
• 2020-, Fellow of The American College of Epidemiology (FACE), USA
• 2020- Fellow of The Obesity Society (FTOS), USA
• 2019, ETSU the University Distinguished Faculty Award for Service Nominee, Tennessee, USA
• 2019, Best Poster Presentation Award, CVD Appalachia Conference, Tennessee, USA, 2019
• 2019, Evidence-Based Optimal Nutrition Certificate, Harvard T. H. Chan School of Public Health
• 2019, Visiting Scientist, Harvard T.H.Chan School of Public Health (Mentor: Dr. Frank Hu)
• 2019, Fellow of The Obesity Society Nominee, USA
• 2019-, Founder and President, Institute of Health Education and Lifecourse Promotion (iHELP)
• 2018, Foundation Service Award, ETSU College of Public Health
• 2017, ISCEP fellow
• 2017, ETSU Dean’s Special Recognition Award for Service for University Leadership Faculty Senate
• 2017, ETSU Dean’s Special Recognition Award for Service on Faculty Council
• 2017, Tennessee Service Award
• 2016-, Founding President. International Chinese Nutrition Young Scholar Network (ICNYSN) (www.icnysn.org)
• 2016-2020, Board Director, China Health Policy and Management Society (CHPAMS)
• 2016-2017, Chair of Public Relation Committee, Chair of Webinar Committee, North American Chinese Society for Nutrition (NACSN)
• 2016, North American Chinese Society for Nutrition (NACSN) Outstanding Leadership and Service Award
• 2015, Invited speaker, 12th China National Nutrition Science Congress, Beijing, May 16-18, 2015
• 2015, Invited speaker and judge for awards competition for the 1st International Congress on Childhood Obesity and Hypertension, Beijing, China, May 29-31, 2015
• 2014, Faculty Mentor of the Year Nominee, 21st Annual Compact for Faculty Diversity Institute on Teaching and Mentoring, Atlanta, GA, USA: Southern Regional Education Board (SREB)-State Doctoral Scholars Program
• 2009, SAS (Statistics Analysis System) Base Programmer for 9.1 Certification
• 2004, Top 5 National Trainee: GlaxoSmithKline Pharmaceutical

 

Degrees

DrPH Epidemiology
MPH Epidemiology
MD Medicine

 

Contact Information

Baylor University
College of Health & Human Sciences
Department of Public Health

One Bear Place #97343
Waco, Texas 76798-7343

Office: Rena Marrs McLean Gymnasium 233
Phone: 254-710-4219
Fax: 254-710-3404
Email: Liang_Wang1@baylor.edu