Today's computer-powered studies allow researchers to look beyond obvious health risks of the past. New analyses show, for example, that finger length, grip strength and even height may be reliable predictors of cancer, longevity and heart disease.
But not all statistically based findings are created equal, said Rebecca Goldin, a mathematician at George Mason University and volunteer for STATS.org.
Apparently things like finger length, grip strength, and height may be reliable predictors of cancer, longevity and heart disease. Don't believe it? Check this weird list of potential risk indicators out anyway. It'll terrify, amaze, and amuse you.
"It's easy to get results that look impressive by trying a whole bunch of things on large databases of information. Things pop out, but they can be completely spurious because of chance," Goldin said. "It's now a fairly common thing to see something published and have someone say that it's not true."
Although the ease of mining medical databases for results can outpace scientists' abilities to review them (clinical trial journals alone publish about 75 in-depth studies every day, yet only 11 reviews of these studies), some do stand up to statistical and cause-and-effect scrutiny.
We recap here some of the weirdest, yet credible, indicators of medical risks ever discovered.
At least two genes - HOXA and HOXD - control testicle development in the womb, and testicles in turn create testosterone. But these two genes also mandate hand development, especially the index and ring fingers.
The discovery has spawned odd testosterone-based hypotheses about what the ratio of the two fingers means, from sexual fitness and exam performance to personality and sporting ability.
Most of the proposals have fallen short of any meaningful significance, but an upcoming study in the British Journal of Cancer suggests there is a significant link to prostate cancer: If the index finger is longer than the ring finger, a man is less likely to develop the cancer.
"It seems strange, but this isn't guesswork," said Rosalind Eeles, a cancer geneticist at the Institute for Cancer Research (ICR) in London and co-author of the study.
Eeles and her team compared more than 1,500 men with prostate cancer against more than 3,000 random men. Ignoring family history and other factors, men older than 60 years with a longer index finger were 33 percent less likely (on average) to develop prostate cancer. Younger men with a longer index finger fared even better, with an 87 percent average reduction in risk.
The association still needs to be tried against other populations to be a meaningful assessment of prostate cancer risk, but Goldin said "its speed and non-invasiveness does have something going for it."
"It's way too early to say how much hand screening could help," said Elizabeth Rapley, a molecular geneticist and spokesperson for ICR. "If anything, it gives us more of a handle on how prostate cancer starts, that testosterone may have big role in the development of the disease."
According to a 25-year study of more than 6,000 men aged 45 through 68, grip strength was the best predictor of well they'd avoid being disabled later in life. The weakest-gripping men suffered twice the disabilities of strongest grippers. And in a separate study of older men and women, good grip strength was correlated with longer lifespan.
But correlation is not causation. The best bet to living a long life, according to a plethora of research, is eating well, exercising regularly and avoiding harmful habits like smoking.
The crud between your teeth may seem innocuous, but study after study has shown chronic infections of the mouth (also called periodontal diseases) increase the risk of circulatory woes, including coronary heart disease.
Mouth bacteria sneaking into in the blood via the gums, the thinking goes, may lead to more heart-clogging arterial plaques. Inflammation caused by such a persistent infection may also prime the body for heart attacks.
If you're close to an airport and can fly cheap, you may get to see more of the world, but this could also increase your risk of developing skin cancer.
During a British economic rebound in the 1970s, Rapley said, people enjoyed the jump in their money's value by traveling abroad.
"Many of them went to the beaches of Spain and spent a lot of time in the sun," she said. "We now see an increase in the rate of melanoma in that population."
First-born boys may be more likely to develop testicular cancer later in life.
"Lots of series of studies suggest the first child is exposed to higher levels of estrogen, which gives greater risk of testicular cancer. But this has never been definitively proven," Rapley said.
Chemicals similar to estrogen are one major suspect for the doubling of testicular cancer in the past 40 years (an increase not from improved screening, she said). Estrogen analogs may get into food and water supplies, for example, via the pesticides they're found in.
Perhaps the strongest medical risk of early birth order is childhood leukemia. It develops more often in older siblings and seems to be tied to socioeconomic status. Rapley suspects immune system training may also be part of the explanation.
"There are suggestions that it may have to do with exposure to viruses and colds and bacteria," she said. Siblings aren't around to give them as much exposure, she said, so "kids who go to child care at an early age are less likely to develop leukemia than kids kept at home."
In assessing any database-powered medical study, Goldin said it's important to look for large sample sizes, proposed causes, accounting for chance and extraneous effects, and acknowledgment of other hypotheses. But putting a health risk into perspective is perhaps the most important thing of all.
"There's a lot of medicine where it's just not clear how helpful it is to know something," Goldin says. "If you're doubling your risk of one in a million, for example, that's still two in a million. Unless it's got some significant impact to way we evaluate treatment, it's hard to see any benefit."
By Dave Mosher