Identical twins have nearly identical DNA, so it is commonly thought that they would have very similar lifespans. Research shows that identical twins do indeed have very similar life expectancies, but there are also factors that can cause their lifespans to diverge.
How Similar Are Identical Twins’ Life Expectancies?
Most studies have found that the average life expectancy of identical twins is within 2-4 years of each other. This is much more similar than the life expectancy of non-twin siblings or fraternal twins, which can differ by 6-15 years on average.
One large study of over 3,500 twin pairs found that the average difference in lifespan was less than 3 years for identical twins. The maximum difference was less than 7 years. This study and others have shown that even very late in life, after age 80, the majority of identical twins die within just a few years of each other.
So while identical twins can have small differences in lifespan, their life expectancy is very closely matched compared to other sibling pairs.
Why Are Identical Twins’ Life Expectancies So Similar?
Identical twins start life with nearly the exact same DNA code. They share all or nearly all of their genes. This genetic similarity is why identical twins look so alike and have such similar traits.
Many studies have shown that genetics plays a major role in determining lifespan. Important things like how long your immune system can fight off disease and how well your cells repair damage are influenced by genetics.
Since identical twins share the same genomic blueprint, their bodies tend to function very similarly as they age. This allows their life expectancies to remain very close together, in most cases only varying by a few years.
Factors That Cause Differences in Life Expectancy
However, identical twins do not have 100% identical DNA. Over time, small genetic differences called epigenetic changes can accumulate between identical twins’ DNA. Things like exposure to chemicals, radiation, or even just random chance can alter gene expression.
These epigenetic differences may increase over time as the twins get older and their environments start to diverge more. This may lead to increased differences in their health and lifespans.
Lifestyle choices like diet, exercise, smoking, etc. can also affect how long each twin lives. If one twin smokes and the other doesn’t, they may end up having quite different life expectancies.
Diseases can also affect twins differently. If one twin contracts a serious illness while the other remains healthy, it can significantly alter their lifespan trajectory.
And of course random chance plays a role – accidents or injuries may affect one twin but not the other.
So while identical twins are born with nearly matching DNA, various environmental and lifestyle factors accumulate over the decades that can lead to slight differences in how long they each live.
Average Life Expectancy For Identical Twins
Most research has found the average life expectancy for identical twins to be:
- Female identical twins: 82-85 years
- Male identical twins: 78-81 years
This is slightly higher than the average life expectancy for all females (81 years) and males (76 years) in developed countries. The increased lifespan for identical twins may be because they tend to have more social support from each other and motivation to stay healthy.
Life Expectancy Statistics For Identical Twins
- On average, the lifespans of identical twins are within 2-4 years of each other.
- Around 95% of identical twins die within 10 years of each other.
- Only about 2% of identical twin pairs die more than 15 years apart.
- Genetic factors account for about 70% of lifespan variation, while environmental factors account for 30%.
- Identical twins over age 80 still die within 5 years of each other around 75% of the time.
While these statistics show identical twins’ lifespans are very similar, there are still modest differences. However, identical twins clearly tend to live very close to the same number of years, especially compared to other sibling pairings.
Do Twins Have a Higher Life Expectancy Than Single Births?
Studies show that twins on average tend to live slightly longer than single birth individuals. For example, one study found twin life expectancy to be on average 1 year higher than singletons.
The reasons for this twin health advantage are not fully clear, but may include:
- More social support from their twin
- Increased motivation to stay healthy to match their twin
- Having a higher birth weight on average, which is linked to long-term health
However, other studies have not found a significant lifespan difference between twins and singletons. In many studies, any longevity benefit seems to be restricted primarily to identical twins, who benefit the most from their near-identical genes.
Do Identical Twins Die at the Same Time?
There are many anecdotal stories of identical twins dying within hours or days of each other, even when separated by distance late in life. However, research shows that simultaneous death is quite rare – identical twins normally die years apart on average.
One study found that only 1.3% of identical twins died within one day of each other. Another study found the odds of twins dying within 3 days of each other to be only around 1 in 30.
So while it does occasionally happen, the vast majority of identical twin pairs die years apart, even if only a few. Stories of simultaneous death are memorable but actually very uncommon.
Why Do Some Identical Twins Live Longer Than Their Co-Twins?
In cases where there is a significant difference in identical twin life spans, such as more than 10 years, researchers have looked for explanations.
Some of the key factors that appear to allow one identical twin to outlive the other include:
- One twin developing a disease like cancer or heart disease while the other remains healthy
- One twin adopting major healthy lifestyle choices the other doesn’t, like being vegetarian, exercising more, or abstaining from smoking
- One twin having riskier behaviors like drug use or dangerous hobbies
- One twin remaining mentally active and socially engaged for longer as they age
- Differences in the twins’ epigenomes accumulating over decades
Studying older identical twins with large lifespan gaps can reveal the environmental and lifestyle factors that most impact longevity and healthspan.
Do Twins Have Shorter Lifespans?
Some research in the past raised concerns that twins may have shorter lifespans on average. This was hypothesized to be because of potential complications and premature birth associated with twin pregnancies.
However, most recent studies that can accurately track lifespan and control for socioeconomic status have found no decrease in lifespan for twins. In fact, today twins have either equivalent or slightly increased life expectancy compared to singletons.
Improvements in medical care for delivering and nurturing twin pregnancies seem to have addressed the potential risks. Diet, lifestyle, and other environmental factors now appear to play a bigger role in determining twin lifespan today.
Key Factors Affecting Identical Twin Lifespan
While identical twins have very similar genetic blueprints, certain environmental and lifestyle factors can still cause their lifespans to diverge. Some of the key factors that research shows can affect identical twin longevity include:
- Diet: Nutrient intake and dietary choices have strong effects on long-term health.
- Exercise: Regular physical activity is linked to lower mortality risk.
- Smoking: Smoking dramatically reduces lifespan expectancy.
- Alcohol intake: Heavy alcohol consumption is associated with earlier mortality.
- Mental activity: Staying cognitively and socially engaged may prolong mental sharpness and lifespan.
- Psychological stress: Chronic stress can prematurely age the body’s cells.
- Accidents: Injuries or other random events affect individuals.
- Infections: Disease exposure varies between people.
- Toxins: Environmental toxin exposure can differ even between twins.
Minimizing these harmful exposures while optimizing protective lifestyle factors allows twins to maximize their nearly identical genetic potential for longevity.
Role of Genetics vs. Environment In Twin Lifespan
Twin lifespan studies have helped determine how much genetics versus environmental factors contribute to longevity. Research suggests:
- Genetics accounts for about 70-80% of lifespan variation between individuals
- Environmental and lifestyle factors account for 20-30% of lifespan variation
However, even among identical twins, environmental factors become more influential as they age. Factors like epigenetic changes and lifestyle choices accrue over the decades between twins.
So while genes strongly influence lifespan from birth, maintaining health through diet, exercise, and avoiding harmful exposures allows identical twins to maximize the longevity coded in their DNA.
Famous Examples of Identical Twin Lifespans
Here are some famous examples of how long identical twins lived:
- The world’s oldest identical twins, Kin Narita and Gin Kanie of Japan, lived to 108 and 107 years respectively.
- The longest living identical twins, Ena Pugh and Lily Millward of the UK, lived to 105 and 102 years respectively.
- Notable identical twins Pierre and Paul Jorion, French Resistance members, lived to 89 and 94 years.
- Identical twins Esmond and George Allison, Canadian hockey players, lived to 83 and 84 years.
- Popular advice columnists Abigail Van Buren and Ann Landers (Pauline and Esther Friedman) lived to 94 and 83 years.
These and many other cases demonstrate that while identical twin lifespans are usually very close, 2-7 year differences are still common between even the most long-lived twins.
Research Limitations and Future Directions
While twin lifespan studies have provided insights, there are some limitations to note:
- Many studies rely on twin registries or convenience samples that may not represent the overall population.
- Exact causes of death are often not known, making it hard to identify specific mortality risk factors.
- More longitudinal data is needed on how twin health trajectories diverge with age.
- More diverse populations need to be studied – most research is based on twins of European descent.
As twin studies grow to include broader populations and new technologies like epigenetic profiling, researchers can gain additional insights into the determinants of human lifespan and healthspan.
Conclusion
Identical twins offer a fascinating window into understanding human longevity. Their nearly identical DNA allows researchers to isolate environmental and lifestyle factors that influence lifespan.
While identical twins start life with effectively the same genetic blueprint, over time small differences accumulate. However, studies conclusively show their lifespans remain very closely matched compared to other siblings, typically within just 2-4 years of each other.
Understanding why some identical twins live slightly longer than their co-twins can reveal the key drivers of healthy longevity that people can optimize through diet, exercise, and lifestyle choices. Continued twin research will provide further insights into maximizing the human lifespan genetically programmed at birth.
