Unlocking Lifelong Health Secrets with the Veteran Twin Registry
What if the secrets to healthy aging, the risks for chronic disease, and the very balance between our genes and our life experiences could be decoded from a single extraordinary group of people? This isn't the premise of a science fiction novel but the real-life story of the National Academy of Sciences-National Research Council (NAS-NRC) Twin Registry, one of the most valuable and longest-running scientific resources in the United States.
For over six decades, this remarkable registry of 15,924 white male twin pairs—all born between 1917 and 1927 and both having served in the military—has quietly transformed our understanding of human health 1 7 .
These World War II veterans, often called "The Greatest Generation," have contributed far more than their military service; they've provided scientists with a unique natural experiment to disentangle the complex threads of genetics and environment that weave the tapestry of our lives. This is the story of how a registry created for one purpose has unlocked discoveries about everything from heart disease to dementia, offering insights that benefit all of humanity.
Twin participants in the registry
Of continuous research
Scientific papers generated
The origins of the NAS-NRC Twin Registry date back to the late 1950s, when the Medical Follow-Up Agency sought to understand the long-term health of veterans 1 . Researchers realized that twins offered a perfect natural experiment for studying the age-old "nature versus nurture" debate. By comparing identical twins (who share nearly 100% of their DNA) with fraternal twins (who share about 50%), scientists could estimate the relative influence of genetics versus environment on various health conditions 1 4 .
Comparing identical vs. fraternal twins allows scientists to separate genetic influences from environmental factors.
All participants were white male twins born between 1917-1927, representing 93% of the U.S. population at that time.
Registry launched by matching birth certificates against Veterans Administration files 7 .
Birth years of all twin participants in the registry.
All participants served in the military during this period.
| Total Twin Pairs | 15,924 pairs (31,848 individuals) |
| Years of Birth | 1917-1927 |
| Military Service | Primarily World War II veterans |
| Demographic | White males |
| Founding Era | Registry launched in 1958-1959 |
| Unique Feature | One of the oldest population-based twin registries in the U.S. |
What makes this group particularly significant historically is that they represent a unique slice of America. As WWII veterans, they were part of what journalist Tom Brokaw termed "The Greatest Generation," characterized by core values of personal responsibility, duty, and overcoming adversity 7 . Importantly, among all U.S. males aged 45-49 in 1970, 71% were WWII veterans, making this group highly representative of the white male population of that era 7 . Their lives were also uniquely shaped by the "GI Bill" that offered veterans tuition for college and low-interest home mortgages, dramatically expanding educational and economic opportunities in ways that influenced their health trajectories for decades 7 .
Over more than six decades of research, the NAS-NRC Twin Registry has yielded extraordinary insights into how genetics and environment interact across a lifetime to influence health and disease. The registry has enabled two powerful types of studies: classical twin comparisons that measure how similar identical versus fraternal twins are for particular traits, and co-twin control studies that compare twins where one has a disease or exposure and the other does not 1 .
| Health Domain | Key Discovery |
|---|---|
| Mental Health | Greater heritability for manic-depressive psychosis than for schizophrenia 1 |
| Neurodegenerative Disease | Stronger genetic component for Alzheimer's than Parkinson's disease 1 |
| Lifestyle Factors | Smoking associated with higher risk of multiple age-related conditions 1 |
| Cognitive Aging | Intelligence and lifespan association largely driven by shared genetics 7 |
| Cardiovascular Health | Blood pressure and heart disease risk show both genetic and environmental influences |
The registry revealed varying levels of genetic influence across different mental health conditions 1 .
Studies revealed smoking as a powerful environmental exposure linked to greater risk of cancer, cardiovascular disease, poor cognition, and eye disease 1 .
NAS-NRC data combined with Swedish and Danish twin registries revealed small but significant association between cognitive scores and age at death across populations 7 .
Among the many research initiatives within the NAS-NRC Twin Registry, the Duke Twins Study of Memory in Aging stands out as a remarkable example of scientific ingenuity. Launched with a simple yet powerful goal—to understand the genetic and environmental influences on cognitive aging and dementia—this long-term study utilized the twin registry in particularly creative ways 7 .
The Duke study employed a sophisticated multi-stage design to identify and diagnose cognitive impairment within the twin population. The process began with a telephone screening using TICS-m (Telephone Interview for Cognitive Status-modified), a validated cognitive assessment tool specifically adapted for epidemiological studies 7 . This efficient approach allowed researchers to screen thousands of twins across the United States without requiring expensive in-person visits.
For twins who scored below a specific cutoff on the telephone screen, or who couldn't complete the interview, the study implemented a proxy interview where a family member or close contact would provide information about the twin's cognitive functioning 7 . The research team then used the Dementia Questionnaire with these informants to determine whether an in-person evaluation was warranted 7 .
| Research Stage | Procedure | Purpose |
|---|---|---|
| Stage 1: Telephone Screening | TICS-m (Telephone Interview for Cognitive Status-modified) | Initial cognitive screening of all available twins |
| Stage 2: Proxy Interviews | Dementia Questionnaire with informants | Gather collateral information on cognitive function |
| Stage 3: In-Person Assessment | Comprehensive clinical and cognitive evaluation | Detailed characterization of cognitive status |
| Stage 4: Consensus Diagnosis | Expert review of all available data | Assign formal diagnoses using standard criteria |
The Duke Twins Study generated profound insights into how genetics and environment shape cognitive aging. By comparing identical and fraternal twin pairs where one or both developed dementia, researchers could estimate the heritability of Alzheimer's disease and other cognitive conditions. The twin design allowed scientists to determine how much of the variation in dementia risk was attributable to genetic factors versus shared or unique environmental experiences.
One of the most powerful aspects of having twin data was the ability to study discordant pairs—where one twin developed dementia while the other remained cognitively healthy. These rare natural experiments provided unique opportunities to identify environmental factors that might protect against or accelerate cognitive decline, even in individuals with similar genetic backgrounds. The study also investigated how early-life factors including education, military service experiences, and midlife health habits might influence cognitive outcomes decades later.
The research design also enabled investigations into the relationship between different aspects of brain health. In addition to screening for cognitive impairment, the second wave of telephone interviews included screening for parkinsonism 7 . This allowed researchers to examine potential genetic and environmental links between different neurodegenerative conditions, expanding our understanding of how various brain aging processes might share common underlying mechanisms.
The enduring value of the NAS-NRC Twin Registry stems not only from the dedicated participants but from the rich array of data and biological materials collected over decades. This comprehensive approach has created a multidimensional resource that continues to yield new discoveries as analytical techniques evolve.
What began as a study of veteran health has evolved into a scientific resource of unprecedented value. The NAS-NRC Twin Registry exemplifies how thoughtfully assembled cohorts can continue generating knowledge for decades beyond their inception. The registry has contributed to approximately 377 publications as of 2015 7 , with findings spanning cardiovascular health, mental illness, neurodegenerative disease, and successful aging.
The legacy of the registry continues to grow through data sharing initiatives. Previously available only through a user fee system at the National Academy of Sciences, the registry data is now freely accessible through the National Archive of Computerized Data on Aging (NACDA) 7 .
The data also contributes to international consortia like the CODATwins Project and the Consortium on Interplay of Genes and Environment across Multiple Studies (IGEMS), allowing researchers to ask questions that no single registry could answer alone 7 .
The story of the NAS-NRC Twin Registry is ultimately about more than scientific discovery—it's about the enduring gift that these veterans unknowingly gave to future generations. Through their participation, these twins have helped decode the mysteries of human health and aging, providing insights that benefit people far beyond their own generation. Their legacy reminds us that sometimes the most powerful scientific resources aren't found in laboratories, but in the lives of ordinary people who volunteer to be part of something extraordinary.
References will be listed here in the final version of the article.