As the saying goes, the best measure of a man's character is the company he keeps. But what about his health? According to Steven Lamm, MD, the best measure of that is his erect penis.

"There's an incredibly important link between a man's health and sexual performance," Lamm, an assistant professor of medicine at New York University, tells WebMD.

Lamm's recent book, The Hardness Factor, is a flashing neon sign pointing to that link.

It is well known that heart disease, as well as diabetes, depression, obesity, substance abuse, and many other health problems can quash erections. Getting an erection isn't crude mechanics, like inflating a balloon. It's a complex process in which blood vessels, muscles, hormones, the nervous system, and the psyche all work together. If one part isn't working well, it affects the whole apparatus.

This isn't another book touting Viagra, like Lamm's The Virility Solution, published in 1998, the same year Viagra hit the market. Lamm says The Hardness Factor is not for men who are already dealing with erectile dysfunction (ED). His aim is to convince young, healthy men to take better care of themselves by speaking to their penises.

"If you want a 28-year-old man to stop smoking, let him read the book," Lamm says.

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