Too often, a man’s penis is the centerpiece of his pant-less legs. But a man’s package is more than just his penis. Testicles (a.k.a. balls) chill in men’s scrotums (or ball sacks) both literally and figuratively — they need to be at a temperature slightly lower than the body’s — where they create sperm cells, which are halfway responsible for human life (that’s rather important, actually). But there’s more to the walnut-sized body part. In fact, a lot of it involves their size, which can tell us some things about the person they belong to.

Bigger Testicles, More Heart Problems

Men with larger testes may be more prone to developing heart disease, a 2013 study on over 2,800 men found. After following up with the men seven years later, the researchers found that those with bigger testes had a higher chance of developing heart disease. Granted, these men were also more likely to drink heavily and have high blood pressure. Along with stress that probably came from being sexually dysfunctional, these men were kind of setting themselves up for a higher risk of heart disease.

Still, the researchers suggested that the reason men with larger testes developed heart problems more often was because of the testosterone-producing hormone called luteinizing hormone, which is responsible for stimulating testosterone production. Studies have linked higher levels of testosterone to heart disease.

Smaller Testicles, No Sleep?

A study from researchers at the University of Southern Denmark found an interesting correlation between a man’s quality of sleep and his testicle size. They surveyed almost 1,000 men about their sleep schedules, sleep interruptions, and sleep habits, and then tested their testicular sizes and sperm counts. They found that those men who reported insomnia, stayed up late, or slept inconsistently had sperm counts that were 29 percent lower. On top of that, their testicles were also 1.6 percent more deformed while also being smaller in size.

It’s obvious that smaller testicles aren’t causing someone to sleep less. The study shows, however, that a person with smaller testicles might not be getting all the sleep they need. The researchers also noted that people who had poor sleep also tended to lead unhealthier lives filled with fatty foods, alcohol, and smoking, among other habits. So, smaller testicles could actually indicate a person is unhealthy in other ways too.

Smaller Testicles, Better Dads

This may be a stretch, but dads who stick around for their kids seem to be the ones with smaller testicles. A study from Emory University interviewed 70 dads with 1- or 2-year-old children. Both father and mother were interviewed about the dads’ involvement in child rearing, including how often they changed diapers, bathed the child, or took them to the doctor when they were sick. They also measured the fathers’ testosterone levels.

Their results showed that dads who were more involved tended to have lower testosterone and thus smaller testicles. “We’re assuming that testes size drives how involved the fathers are,” anthropologist Dr. James Rilling said. “But it could also be that when men become more involved as caregivers, their testes shrink. Environmental influences can change biology. We know, for instance, that testosterone levels go down when men become involved as fathers.”

What does this mean for men’s health? Well, seeing as dads are more nurturing, chances are they have better relationships with their children, which in turn translates to better mental health for them.

Testicular Cancer

No story on the testicles and health should leave out perhaps the most important health indicator the testicles can provide: a testicular cancer self-exam. In 2014, there will be an estimated 8,820 new cases of the cancer, with 380 deaths, according to the American Cancer Society. While that number is small, the only reason is because treatment options are widely available and effective. Nevertheless, it’s a cancer that can affect one or both testes, where it appears as a lump on the testicle, an enlarged testicle, a heaviness in the scrotum, an aching pain in the lower abdomen or groin, or a collection of fluid in the scrotum.

The cancer can affect men at any age, though it appears most often around 20 to 34 years of age, especially among white men, who face a risk four to five times that of black men. If you didn’t know already, you can check for testicular cancer by yourself after each bath or shower. To perform the self-exam, follow these steps from the Cleveland Clinic:

1.       Do the exam after a warm shower or bath. The warmth relaxes the skin of the scrotum, making it easier to feel for anything unusual.

2.       Use both hands to examine each testicle. Place your index and middle fingers underneath the testicle and your thumbs on top. Roll the testicle between your thumbs and fingers. (It's normal for testicles to be different in size.)

3.       As you feel the testicle, you might notice a cord-like structure on top and in back of the testicle. This structure is called the epididymis. It stores and transports sperm. Do not confuse it with a lump.

4.       Feel for any lumps. Lumps can be pea-size or larger and are often painless. If you notice a lump, contact your health care provider.

5.       Although the left and right testicles are often different sizes, they should remain the same size. If you notice a change in the size of your testicles, contact your health care provider.