I have more than passing interest in left-handedness. Some of my favorite people — my daughters, actually! — are left-handed. So, when I heard that lefties are prone to certain health problems, I took notice.
But, I was also skeptical as much of what I heard is not taught in medical school. And it did not sound biologically or logically plausible.
Have you heard these "facts" about left-handed people?
- They don't live as long as right-handed people.
- They have more cancer.
- They have more heart and blood vessel disease.
- They have more accidents.
Not all of the things that supposedly make lefties unique are bad. I've also heard that:
- They're more likely to become president. (Check out Mr. Obama the next time he signs a bill or takes a jumpshot.)
- They're more artistic.
- They have an advantage in sports.
I'll address some of these in a bit. But first, some background on handedness.
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What Determines Handedness?
It's surprising to me that so much is unknown about what determines whether you're right-handed, left-handed or mixed-handedness (ambidextrous).
Handedness is controlled by the “motor cortex,” a swath of brain tissue at the back of the frontal lobes. This part of the brain may make its preference known for one hand or the other in kids as young as age 2. But, handedness may not be fully developed until age 9. Perhaps that’s why many people can learn to use their non-dominant hand for tasks or sports if they start young. Tennis star, Rafael Nadal, and pro golfer, Phil Mickelson are good examples of this – both are naturally right handed but perform at the highest levels of their sports as lefties.
It's thought that, as with most behaviors, one or more genes and the environment interact in an important way. While people who are left-handed tend to have at least one left-handed relative, scientists have not yet identified a gene or combination of genes that play a role in determining handedness.
If a gene or environmental factor is discovered to play a role in driving handedness, it will have to explain some interesting correlations between handedness, brain control of language and hair growth. Yes, hair growth. Here's why:
- Ninety percent of people are right handed.
- The brains of 90% of right-handed people and 75% of left-handed people are "left-dominant" (that is, the left side of the brain controls language).
- Ninety percent of right-handed people have hair that "spins" clockwise, but it's random among lefties — only 50% of them have a clockwise "whorl" on top of their heads.
Now that the human genome has been unraveled, we may soon find out how handedness is selected. For now, however, it's a pretty mysterious thing!
In fact, there's much about handedness that's mysterious. Perhaps that's why, historically, lefties have been viewed with suspicion. Even the technical name for left-handedness — sinistrality — comes from the latin word "sinistra" that also means evil or unlucky. And maybe that's why it used to be common for teachers to try to change left-handed kids into right-handed kids.
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The idea that left-handed people have shorter life spans than right-handed people is not new. It comes, in part, from the observation that as a population ages, the percentage of left-handed people falls. If you gather a large group of young adults together, about 10% to 15% will be left-handed. But, left-hand preference will be reported by about 5% of 50 year-olds and only 1% of 80 year-olds.
Is this because of an earlier demise of left-handed people? Is it because lefties cannot survive as long “in a right-handed world? For example, there might be more accidents among people using power tools designed for right-handed workers.
Maybe whatever causes left-handedness — perhaps a stressful event during fetal development — also causes lefties to suffer certain health problems more than righties. Yet another theory is that lefties live just as long, but describe themselves as right-handed due to stigma, superstition or because they were forced to switch handedness as a child.
Several studies have examined the longevity issue. Some found higher death rates among left-handed people, some found a longer lifespan for lefties, and many found no relationship at all. For example, a remarkable study of Danish twins published in 2000 found no difference in death rates of twins in which one was right-handed and other was left-handed. A 2008 study among major-league baseball players also found no effect of handedness on longevity.
But, there are older studies showing righties live longer. For example:
- A study of baseball players and one of cricket players concluded that left-handed players have shorter lifespans than right-handed players.
- Among the most recent studies is one published in the medical journal Epidemiology in 2007. It found that left-handed women did not live as long as otherwise similar right-handed women. They had significantly higher rates of colorectal cancer and heart and blood vessel disease.
- Another 2008 study found that among elderly patients in a cardiac rehabilitation unit, left-handed people were over-represented. The authors suggest that a higher rate of heart disease among lefties might explain their shorter lifespans.
As I review the evidence, I think it's uncertain whether righties truly live longer or whether they just appear to do so. And if lefties don't live as long, it's uncertain why.
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Several studies have explored whether there is a difference in the incidence of accidents between right and left-handed people.
A 1989 study surveyed nearly 1,900 college students and found that lefties reported more accidents (especially car accidents) than righties. The authors of this study suggested that it was due to environmental factors, such as the way common implements (from scissors to gearshifts), traffic patterns and power tools are designed for the right-handed majority.
Another study that enrolled nearly 1,000 people living in southern California found that, on average, righties lived nine years longer than left-handed people. In that study, the risk of death by accident was nearly six times higher for lefties; the risk of dying in a car accident was four times higher.
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While it’s often said that left-handed people are more artistic than righties, it’s hard to find conclusive data to support this. Sure, there are some superstar left-handed artists, such as Michelangelo, Da Vinci and Rubens.
But are lefties really more artistic? It's hard to know. The logic goes like this: Left-handed people are less left-brain dominant and use more of their right brains, the "creative" side. I did run across a 2000 study reporting that lefties scored better on tests of creative problem-solving. Still, this is hardly conclusive.
I also found studies reporting a higher than expected prevalence of left-handedness among scientists and mathematicians. In the study finding more creativity among lefties, the researchers found left-handed people were over-represented among those with the highest IQs. However, the left-handed subjects also performed worse on tests of memory. While it's easy to find claims of intellectual and creative differences between left- and right-handed people, it's much harder to find convincing support for them.
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In certain sports, lefties seem to have an advantage: Baseball and tennis come to mind. There are also studies suggesting that left-handed boxers and fencers are more successful. Is this because they're actually better than their right-handed adversaries or because their opponents are so accustomed to facing righties? That's not easy to answer. But, it may be the latter:
- A 2009 study of tennis players found that right- and left-handed athletes predicted the direction of a right-handed opponent's shot better than when the opponent was left-handed.
- In non-interactive sports, such as golfing or swimming, left-handedness does not seem to provide an advantage.
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The 2008 election between John McCain and Barack Obama guaranteed that the United States would have a left-handed president, as both are lefties. Some have suggested that this represents a trend as five of the last seven presidents have been left-handed. If so, it's a relatively new trend: Only two presidents before 1974 were left-handed.
One theory suggests that lefties recognize early on they are unique compared with others around them. For some, that sense of "specialness" might translate into comfort taking leadership roles. Even if that's true, no one can really say that left-handedness will ease your road to the White House.
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The Bottom Line
As I've learned more about handedness, I'm left with these conclusions:
- More research is needed to understand what determines handedness and whether it affects health or longevity.
- If handedness does affect lifespan, it's not clear how much you can do about it.
- It's not clear you can or should change your hand preference. There’s no evidence that trying to switch your dominant hand will have a beneficial effect on your health or lifespan.
- Even if the average lifespan of left-handed people is shorter, it's probably not by much — and plenty of people who are left-handed live rich, full lives.
The more I learn about handedness, the more interesting — and mysterious — it becomes. But, until more is known, don’t believe everything you hear about lefties having a shorter lifespan than righties.
As for my left-handed daughters, I'm not convinced they are at any particular health risk or have any particular advantage or disadvantage because of their handedness. Then again, I may need an excuse when they beat me at tennis.
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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.