Chronic obstructive pulmonary disease, aka COPD, affects more than 12 million Americans and is the third-leading cause of death in the U.S.
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Leonard Nimoy, the beloved actor, photographer, and director who was most well-known as Mr. Spock on Star Trek, died Friday morning at age 83, after "a long battle" with chronic obstructive pulmonary disease (COPD), People magazine reported.

Never heard of COPD? You're not alone. Although it’s the third leading cause of death in the United States, causes No. 1 and No. 2 (heart disease and cancer) are much better known. COPD includes two lung conditions, emphysema and chronic bronchitis, which cause symptoms like shortness of breath, wheezing, and chronic cough, among others. More than 12 million Americans currently have the disease, but another 12 million have COPD-like problems, but are undiagnosed.

The most common cause of COPD is smoking, which Nimoy was very vocal about. The Internet's honorary Grandfather announced last year that he was suffering from the disease, tweeting that he wished he had quit sooner:

A week later, he echoed that message, signing off as always with LLAP, shorthand for his hallmark phrase "Live long and prosper."

And Grandpa Nimoy was right: Tobacco smoke inflames and damages the airways, affecting a person’s ability to breathe normally, leading to COPD. About 20% of long-term smokers will go on to develop some form of it. Long-term exposure to other lung irritants like chemical fumes and air pollution can also contribute to COPD.

Many people with COPD can manage symptoms with drugs like inhaled steroids and bronchodilators (which relax the muscles in your airways, making breathing easier), but the disease is progressive, which means it gets worse over time. It often leads to disability—even walking or putting on clothes can leave a person breathless. It's also associated with serious complications, including diabetes, high blood pressure, heart attacks, and exacerbations, episodes in which symptoms dramatically worsen due to an infection or other trigger.

People reported earlier last week that Nimoy was taken to a Los Angeles-area hospital after experiencing severe chest pain. His granddaughter later confirmed that he had end-stage COPD.

An avid Twitter user, Nimoy would post his own poetry and interesting thoughts to the social media site, while keeping his followers updated on his condition.

The Monday before his death, Nimoy left this final sentiment about the ephemeral nature of life.