Simply looking at the length of someone's fingers can reveal surprising insights into their health, say researchers.

Several studies have shown that the amount of testosterone a fetus is exposed to influences their finger length — adults whose index fingers are shorter than their ring fingers were exposed to greater amounts of testosterone when they were in the womb.

It's referred to as the 2D:4D ratio, and is the ratio of the index finger (second digit) to the ring finger (fourth digit). It's calculated by dividing the length of the index finger by the length of the ring finger.

"The relationship between the index finger and ring finger in particular indicates how much testosterone you have been exposed to in utero," says Carl Pintzka, a medical doctor and researcher at Norway's National Competence Service for Functional MRI.

Prostate cancer. A study published in the British Journal of Cancer found that men whose index fingers were longer than their ring fingers lowered their risk for prostate cancer by a third. The news was even better for men under the age of 60 — their risk was 87 percent less.

Those with short ring fingers may also have an edge on their longer-fingered brothers when it comes to surviving the disease. Studies show that men with short ring fingers respond better to dutasteride, a drug that treats prostate cancer by blocking the effects of testosterone on the prostate.

In the study, which was published in the British Journal of Urology, men with benign prostatic hyperplasia (BPH) took dutasteride, which is also used to treat BPH, for six months. When their prostate glands were measured, men with short fingers had a much bigger reduction. "These results suggest finger length might predict the response to dutasteride treatment," the researchers wrote.

Heart disease. A longer ring finger indicates a lower risk of early heart disease. A study published in the International Journal of Obesity found that testosterone was protective against heart attacks in men, but the correlation didn't apply to women.

Depression. A study published in Personality and Individual Differences found lower levels of testosterone, which tends to make index fingers longer in comparison to ring fingers, are associated with an increased risk of depression and anxiety in men. The trait has also been associated with an increased risk of schizophrenia.

ADHD. Short index fingers and long ring fingers, which are associated with higher levels of testosterone, show an increased risk of developing diseases that are more common in men, such as ADHD, Tourette's, and autism.

Obesity. Previous research found that testosterone levels can protect against obesity as an adult, and high testosterone levels as a fetus appear to train the body to fight fat in the future. A study published in the International Journal of Obesity found that men with long ring fingers (a lower 2D:4D ration), tend to weigh less than men with a higher finger ratio.

ALS. Researchers at King's College London found that people who have amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease, the most common form of motor neuron disease, tend to have longer ring fingers. Motor neurons depend on testosterone to survive, and researchers believe that high levels of testosterone before birth may make adult motor neurons less sensitive to testosterone. The study was published in the Journal of Neurology, Neurosurgery and Psychiatry.

Athletic ability. Athletes tend to have shorter index fingers coupled with longer ring fingers. Dr. John Manning, who has published several articles showing the link between finger ratios and athletic ability, has correctly predicted the winners of sprinting races simply by comparing photographs of the competitors' hands.

Physical aggression. It's probably no surprise that a study published in the journal Biological Psychology found that men with ring fingers longer than their index fingers — thus more testosterone — were more likely to be aggressive than men whose index fingers were longer.

In addition, your finger length may also indicate your economic well-being. A study published in the journal Economics and Human Biology found that longer ring fingers were linked to an increased ability to make money.