Profile

Hi I'm Rik (Rikuta Hamaya), MD, PhD, MS.

Instructor, Division of Preventive Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School

My research areas include CVD/hypertension prevention, prevention trial, heterogeneous treatment effect, and nutrition/ physical activity.

Thank you for viewing my profile!

Research Interests + representative work

1: Application and methodological development for interpreting trials

One of my primary methodological interests is advancing causal inference in randomized controlled trials (RCTs). While intention-to-treat analyses are typically considered the standard, they rarely capture the full spectrum of evidence. My research focuses on leveraging state-of-the-art statistical approaches to expand the interpretability of RCTs. For example, I have summarized methodological frameworks to assess heterogeneous treatment effects (HTEs) and applied these to the POUNDS Lost trial, successfully developing individualized treatment rules (A). I extended these approaches to a large primary prevention trial of omega-3 fatty acids, where I created a clinically intuitive scoring system to guide supplementation for coronary heart disease prevention (B). Building on these applications, I have conducted theoretical work to improve the efficiency and generalizability of HTE estimation (C). Additionally, I have employed Bayesian frameworks to provide more intuitive interpretations of RCT findings (D).

A: Hamaya R, Hara K, Manson J, et al. Machine-learning approaches to predict individualized treatment effect using a randomized controlled trial. Eur J Epidemiol. 2025;40(2):151-166.

B: Hamaya R, Cook N, Sesso H, et al. Identification of individuals who benefit from omega-3 fatty acid supplementation to prevent coronary heart disease: A machine-learning analysis of the VITAL. Eur J Epidemiol. 2025;40(7):803-813.

C: Hamaya R, Suzuki E, Hara K. Generalizable estimation of conditional average treatment effects using Causal Forest in randomized controlled trials. arXiv:2506.12296.

D: Hamaya R, Cook N, Sesso H, et al. A Bayesian Analysis of the VITAL Trial: Effects of Omega-3 Fatty Acid Supplementation on Cardiovascular Events. Am J Clin Nutr. 2025;121(5):1046-1053.

2: Research on nutrition and biomarkers for CVD/hypertension prevention

I have investigated the complex interplay between diet, circulating biomarkers, and cardiometabolic risk. My work on circulating trimethylamine-N-oxide (TMAO) provided pivotal evidence against its use as a cardiovascular risk marker, reshaping clinical perspectives at the time (A). I have also studied determinants of circulating branched-chain amino acids and their associations with inflammation and cardiovascular disease (B). Using high-dimensional data, I comprehensively examined metabolomic pathways related to dietary sodium intake, discovering metabolites related to biotin, propanoate, lysine, and BCAA pathways are involved (C). Currently, I am leading analyses of dietary intervention effects on blood pressure and hypertension the biological mechanisms in prevention trials (D).

A: Hamaya R, Ivey KL, Lee DH, et al. Association of diet with circulating trimethylamine-N-oxide concentration. Am J Clin Nutr. 2020;112(6):1448-1455.

B: Hamaya R, Mora S, Lawler PR, et al. Association of Plasma Branched-Chain Amino Acid With Biomarkers of Inflammation and Lipid Metabolism in Women. Circ Genom Precis Med. 2021;14(4):e003330.

C: Hamaya R, Sun Q, Li J, et al. 24-h urinary sodium and potassium excretions, plasma metabolomic profiles, and cardiometabolic biomarkers in the United States adults: a cross-sectional study. Am J Clin Nutr. 2024;120(1):153-161.

D: Hamaya R, Li S, Lau J, et al. Long-term effect of cocoa extract supplementation on incident hypertension. Hypertension. 2025;82(10):1653-1662.

3: Research on dynamic arterial/coronary blood flow

I have conducted extensive clinical studies on coronary physiology and revascularization strategies. I was the first to propose and validate thermodilution method-based coronary flow capacity (CFC), a novel invasive metric of coronary flow, which has since shown promise for guiding revascularization decisions in patients with stable angina (A, B). I have further applied causal inference methods to assess how revascularization impacts epicardial and microvascular flow (C). More recently, I have extended this line of inquiry to dynamic blood pressure variability, examining its role in aging and dementia risk (D).

A: Hamaya R, Yonetsu T, Kanaji Y, et al. Diagnostic and Prognostic Efficacy of Coronary Flow Capacity Obtained Using Pressure-Temperature Sensor-Tipped Wire-Derived Physiological Indices. JACC Cardiovasc Interv. 2018;11(8):728-737.

B: Hamaya R, van de Hoef TP, Lee JM, et al. Differential Impact of Coronary Revascularization on Long-Term Clinical Outcome According to Coronary Flow Characteristics: Analysis of the International ILIAS Registry. Circ Cardiovasc Interv. 2022;15(6):e011948.

C: Hamaya R, Mittleman MA, Hoshino M, et al. Prognostic Value of Prerevascularization Fractional Flow Reserve Mediated by the Postrevascularization Level. JAMA Netw Open. 2020;3(9):e2018162.

D: Ma Y, Zhang Y, Hamaya R, et al. Baroreflex Sensitivity and Long-Term Dementia Risk in Older Adults. Hypertension. 2025;82(2):347-356.

4: Research on physical activity

Current physical activity guidelines emphasize moderate-to-vigorous physical activity (MVPA), yet step counts are increasingly recognized as a pragmatic alternative. In the Women’s Health Study, I conducted the first head-to-head comparison of MVPA and step counts, demonstrating comparable utility in predicting mortality and cardiovascular disease (A). In the same data, I evaluated the impact of daily step patterns in relation to health, showing that step volume is the primary health determinants over the frequency of days/week achieving a particular step threshold (B). These findings, widely covered by the media, supported incorporating both metrics into public health guidelines. I have also studied long-term smartphone-recorded step data in relation to cardiovascular risk factors (C) and evaluated the effectiveness of a large-scale mHealth application on daily activity and cardiovascular risk biomarkers (D).

A: Hamaya R, Shiroma E, Moore C, et al. Time- vs Step-Based Physical Activity Metrics for Health. JAMA: Intern Med. 2024;184(7):718-725.

B: Hamaya R, Evenson K, Lieberman D, et al. Association between frequency of meeting daily step thresholds and all-cause mortality and cardiovascular disease in older women. Br J Sports Med. 2025;59(24):bjsports-2025-110311.

C: Hamaya R, Mori M, Miyake K, Lee IM. Association of Smartphone-Recorded Steps Over Years and Change in Cardiovascular Risk Factors Among Working-Age Adults. J Am Heart Assoc. 2022;11(14):e025689.

D* Hamaya R, Fukuda H, Takebayashi M, et al. Effects of an mHealth App (Kencom) With Integrated Functions for Healthy Lifestyles on Physical Activity Levels and Cardiovascular Risk Biomarkers: Observational Study of 12,602 Users. J Med Internet Res. 2021;23(4):e21622.

Education & Training

PhD in Population Health Science – Cardiovascular Epidemiology. Harvard University, 2023

MS in Biostatistics. Harvard University, 2023

MS in Epidemiology. Harvard T.H. Chan School of Public Health, 2019

MD & BSc. Tokyo Medical and Dental University, 2013

Completed internal medicine residency: Tokyo Medical and Dental University Hospital

Completed cardiology fellowship: Tsuchiura Kyodo General Hospital

Awards & Grants

Finalist, Elizabeth Barrett-Connor Research Award, American Heart Association Scientific Session, 2024

Research Award, Fuji Foundation for Protein Research, 2022

Certificate of Distinction, Harvard T.H. Chan School of Public Health, 2021

Research Fellowship, The Uehara Memorial Foundation, 2019

Research award, Tokyo Medical and Dental University, 2018 & 2019

Best Presentation Award, Functional Revascularization Encouraged by Optimal Diagnostic Strategy Live, 2018

Overseas Scholarship, The Nakajima Foundation, 2017

Best Poster Award, European Society of Cardiology Congress, 2017

Platinum Award, Beyond Angiography Japan XXI, 2016

Teaching

Clinical Data Science: Design and Analytics, Harvard Medical School: 2024-present

Introduction to Machine Learning and Risk Prediction, Harvard T.H. Chan School of Public Health: 2022-2024

Research Synthesis & Meta-Analysis, Harvard T.H. Chan School of Public Health: 2020-2024

Cardiovascular Epidemiology, Tokyo University of Science: 2020-2026

Publications

Please see here in Pubmed

This website

The other contents in this website are written in Japanese - about causal inference methods, nutrition evidence, etc.