Does Being a Lefty Affect Health, Creativity -- and Sexuality?

From the WebMD Archives

Sept. 8, 2000 -- The desks in grade school, the notebooks, the penmanship lessons. For those who are left-handed, life is an adaptive process that begins early. Says one friend, "Teachers tell you, 'Use the hand you eat with.' I did! But they kept wanting me to use my right hand."

Lefties grow up feeling different, and eventually treasure their uniqueness. Browse the Internet and you will find hundreds of famous lefty names: Leonardo da Vinci, Ringo Starr, Babe Ruth, Albert Einstein. A whole tennis tournament: Martina Navratilova, Monica Seles, John McEnroe, Jimmy Connors. Even Jack the Ripper was a leftie. Who knew?

What causes us to be left- or right-handed? And do lefties really have a greater risk of certain disorders and diseases, as some studies have shown? Are lefties more creative? Can being left-handed even influence sexual orientation -- as a new study suggests?

Or are lefties wired very much like the rest of us and at no greater risk of anything simply because they favor the left hand, as Paul Satz, PhD, chief of the neuropsychology program at UCLA's Neuropsychiatric Institute, tells WebMD.

The debate goes on. Case in point: In the August issue of the journal Psychological Bulletin, researchers report finding a "significant" relationship between handedness and sexual orientation. Compared with heterosexual participants, gays had 39% greater odds of being non-right-handed, writes study author Martin L. Lalumière, a researcher in the Centre for Addiction and Mental Health at the University of Toronto.

Handedness is observed quite early in development. Left-handedness is more common in men than in women, and tests of fetuses (using ultrasound) show 92% sucking their right thumbs, a figure that mirrors prevalence in the adult population, writes Lalumière.

What causes us to be left- or right-handed, however, is undecided. Here are the theories:

  • Genes. Much research points to a genetic influence, yet studies of twins have complicated that theory. Whereas identical twins have identical genes, an analysis of 13 identical and fraternal twin studies -- ranging from 1933 to 1985 -- showed that only 76% (of the expected 100%) of identical twins are both left-handed.
  • Too much fetal testosterone. One theory suggests that high levels of testosterone in the uterus -- possibly caused by stress during pregnancy -- damage or slow the development of the normally dominant left half of the brain, causing some functions to shift to the right half of the brain, which governs visual-spatial, creative abilities like math, music, art, and architecture. Lefties were considered at higher risk of immune diseases, since high testosterone levels can inhibit immune system development. This theory has largely been disproven.
  • Developmental instability in the uterus. Some researchers now think that something indeed happens to change the fetus' "ecological environment" during pregnancy, something that governs handedness and brain organization in general. Although they have not yet figured out the mechanism, they feel that the fetus' vulnerability to environmental stressors -- things that cause disease, like bacteria, pollutants, and stress during pregnancy, as well as genetic mutations -- can cause this instability.

Continued

This newer concept of developmental instability has spawned new studies, writes Lalumière. Other research has shown that left-handed people have fewer offspring, higher numbers of spontaneous abortion, lower birthweight, higher numbers of serious accidents, higher rates of serious disorders -- and a generally shorter lifespan.

Left-handed people have been shown to have more disorders involving the nervous system, autism, stuttering, cerebral palsy, mental retardation, epilepsy, and schizophrenia. They also tend to have some minor physical anomalies -- like low-set ears and mismatched fingers, Lalumière points out in his study.

Says Satz, "Lefties throughout the decades, throughout the millennia, have always been given a bad rap. Being left-handed has always been in the spotlight as a harbinger of something terrible."

Left-handed people are no more likely to have immune disorders, dyslexia (or any other learning disability), driving accidents, homosexuality, breast cancer -- or creativity, for that matter, Satz tells WebMD. "Being a leftie is not a marker for creativity. That's sort of nonsense. Creative geniuses have been left-handed and right-handed. Lefties in the population have basically the same level of [thinking] skills as right-handed people. They also live as long. Being left-handed has nothing to do with it."

Some 20 years ago, Satz was virtually alone in challenging the theory that too much fetal testosterone caused left-handedness and a number of other developmental problems. Since then, he and others have led numerous large studies disproving aspects of the theory, he says.

Many studies linking left-handedness with an assortment of characteristics are very often the result of "cultural bias," Satz says. Also, "too many studies are flawed, or small, or don't take into account people who have shifted to right-handedness." Very often, he says, a link with left-handedness is a "chance finding" in an ambitious researcher's database -- a finding that may be meaningless.

He believes that left-handedness is largely genetic, but that "within the 10% of the population that is left-handed, there is a subgroup of people who masquerade as left-handed but are genetically right-handed. They are individuals who [either] during prenatal development, or the early perinatal period, or in the early postnatal years had some sort of insult to the left [half of the brain], whether it was exposure to a toxin, second-trimester influenza, a small stroke that didn't cause any paralysis. That child grew up to be [a] left-hander."

Continued

Most of the in-uterus "insults" don't seem to negatively affect immune development, he tells WebMD. And as for thinking ability, "there's nothing wrong with them. Their cognitive function is like everyone else's. Because the insult happened early in development, these children are able to recover and the brain becomes reorganized such that the right [half of the brain] takes over some or most of speech and language function."

While being left-handed may not increase any health risks, it may indeed affect brain function. Some researchers remain convinced that left-handed people are indeed wired differently. One study looking at more than 900 patients with Alzheimer's disease compared left-handers with right-handers who had the same degree of dementia, says study author Rachelle S. Doody, PhD, the Effie Marie Cain professor of neurology in Baylor College of Medicine's Alzheimer's Disease Research Program in Houston.

Her study closely screened for "true lefties" -- those who were born left-handed but had been taught to "write right." After matching them with people who had the same degree of dementia, the same education, and the same age, the researchers analyzed the disease progress in each group. While the disease "looked very similar," Doody tells WebMD, "we got the impression that it might have started at a younger age on average in people who were left-handed -- but progressed more slowly over time. So it may speak to some kind of vulnerability."

Left-handed people tend to distribute functions more widely throughout their brain, says Doody. "Strongly right-handed people, if a large part of their left language [part of the brain] is removed or damaged, really lose their language ability. Left-handed people (whose language function is located in the right [half of the brain]) will have some residual language function."

WebMD Health News
© 2000 WebMD, Inc. All rights reserved.

Pagination