Cigarette smoking among adults in the U.S. dropped from 20.9 percent in 2005 to 17.8 percent in 2013, according to new data published by the Centers for Disease Control and Prevention.

That's the lowest prevalence of adult smokers since the CDC began keeping such records in 1965. It translates to about 42 million smokers today, down from 45 million in 2005.

Though the adult smoking rate has dropped, cigarette consumption remains a major public health issue. It's the leading preventable cause of disease and death in the United States, killing more than 480,000 Americans each year.

Just as worrisome, rates for other forms of smoking tobacco, which are also deemed dangerous, including cigars and hookahs, are not declining. In some populations, especially young adults and adolescents, use may even be increasing.

According to surveys, roughly 70 percent of smokers want to quit, and research shows that quitting completely at any age has health benefits. The key — and toughest part — is the smoker needs to quit completely.

"Though smokers are smoking fewer cigarettes, cutting back by a few cigarettes a day rather than quitting completely does not produce significant health benefits," said Brian King, a senior scientific adviser at the CDC. "Smokers who quit before they're 40 years old can get back almost all of the 10 years of life expectancy smoking takes away."

Body of Knowledge

The body's bone marrow produces 3 million blood cells every second — and destroys the same number.

Get Me That, Stat!

Just 30 percent of Americans with HIV had the virus under control in 2011, and approximately two-thirds of those whose virus was out of control had been diagnosed but were no longer in care, reports the CDC. The new study underscores the importance of making sure people with HIV receive ongoing care and treatment and other information and tools that help prevent transmission to others, as well as the need to reach more people with HIV testing.

Doc Talk

CC: chief complain, the patient's primary concern.

Mania of the Week

Opsomania: abnormal love for one kind of food.

Never Say Diet

The speed-eating record for Key lime pie is 10.6 pounds in eight minutes, held by Patrick Bertoletti. Warning: Most of these records are held by professional eaters; the rest are held by people who really should find something better to do.

Observation

"After you find out all the things that can go wrong, your life becomes less about living and more about waiting." — author Chuck Palahniuk in his 2001 novel, "Choke"

Medical History

This week in 1827, the Boston School Committee voted to require, effective in the new year, public school students to show that they had been vaccinated against smallpox prior to school entrance. Certificates were issued for free vaccinations, if necessary. The initiative came just three decades after Edward Jenner's discovery of a method to immunize against smallpox. Massachusetts approved the first statewide school vaccination law in 1855, followed by New York in 1862 and Connecticut in 1872.

Curtain Calls

In 1992, a 38-year-old tourist named Greg Austin Gingrich was visiting the Grand Canyon with his teenage daughter. At one sightseeing spot, he leaped atop the guard wall and windmilled his arms, playacting that he was losing his balance to scare his daughter. Then he comically "fell" off the wall on the canyon side, assuming he would land safely on the short slope below.

His daughter studiously ignored him, trying not to fuel her father's dangerous antics. He never reappeared. Gingrich missed his footing, falling silently and fatally 400 feet into the void.

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