Study Finds No Safe Level of Smoking

Posted on December 13, 2016 by Dr. Francis Collins

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Many Americans who’ve smoked cigarettes have been successful in their efforts to quit. But there’s some bad news for those who’ve settled for just cutting back: new evidence shows there’s no safe amount of smoking. One cigarette a day, or even less than that, still poses significant risks to your health.

A study conducted by NIH researchers of more than 290,000 adults between the ages of 59 and 82 found that those who reported smoking less than one cigarette per day, on average, for most of their lives were nine times more likely to die from lung cancer than those who never smoked. The outlook was even worse for those who smoked between one and 10 cigarettes a day. Compared to never-smokers, they faced a 12 times greater risk of dying from lung cancer and 1½ times greater risk of dying of cardiovascular disease.

The findings, reported by Maki Inoue-Choi of NIH’s National Cancer Institute, Rockville, MD, and colleagues, come from an analysis of data from the NIH-AARP Diet and Health Study. The study is evaluating the effects of diet and lifestyle on cancer risk over many years in a large group of seniors from across the country.

The study began about 20 years ago, when a team of NIH researchers mailed questionnaires to 3.5 million members of AARP. More than a half million people answered the original survey. Since then, these respondents have completed two follow-up surveys about their lifestyle and behaviors, including their smoking patterns from ages 15 to 70.

As published in JAMA Internal Medicine, the latest analysis included more than 290,000 seniors who answered a survey conducted from 2004 to 2005 [1]. The participants, divided up about evenly between men and women, included approximately 111,000 never smokers, 156,000 former smokers, and 22,000 current smokers.

Of the current smokers, more than 7,300 were defined as light smokers, which was defined as consuming 10 or fewer cigarettes per day. Within that group, about 1,300 said they smoked less than one cigarette per day on average, while more than 6,000 reported smoking between one and 10 cigarettes per day. Importantly, many also indicated that they had been light smokers for years.

After more than six years of follow up since the survey, more than 37,000 respondents had passed away. The research team identified the causes of death from a national database, and they began their analysis.

The researchers found that those who reported smoking less than one cigarette per day on average over many years were 64 percent more likely to die from any cause than those who never smoked. Those causes included lung cancer, numerous cardiovascular diseases, and many respiratory conditions. People who reported smoking between one and 10 cigarettes each day were almost twice as likely to die from any cause.

The researchers also discovered the strongest link between long-term light smoking and lung cancer. However, those who consistently smoked 10 or fewer cigarettes per day also showed a greater risk of dying from respiratory diseases and cardiovascular disease.

Former light smokers who quit at a younger age showed lower risks of dying than did those who had quit more recently. In other words, the benefits of quitting for light smokers added up over time. They didn’t come immediately.

The study does have some limitations. For example, the researchers relied on people accurately recalling behaviors that span many decades. Other health behaviors like diet and exercise might have correlated with cigarette smoking, and might account for some of the differences in outcomes. Most of the participants were also older, white, and belonged to specific age groups. So it’s unclear how well the findings apply to all Americans.

Those limitations aside, it’s clear that even light smoking can have major health consequences. It’s a finding that’s broadly consistent with evidence linking regular exposure to secondhand smoke to a range of health problems, including cancer and cardiovascular disease.

While the number of smokers in the United States has declined in recent years, the number of light smokers has actually increased. As the researchers noted, one reason for the rise is many people—and young people in particular—seem to have the mistaken impression that smoking an occasional cigarette is relatively safe.

The new findings, therefore, offer a timely warning that there really is no safe level of smoking. They also come on the heels of another report out of the NIH-AARP Diet and Health Study, which found that people who quit smoking in their 60s were less likely to die than those who continued into their 70s [2]. My own father is an example of this—he was a smoker until age 60, when he began to develop chronic bronchitis. After throwing away the cigarettes, his lung function steadily improved, and he lived to the age of 98.

So, there’s a bright side woven through both of these papers. Regardless of how little you smoke or how long you’ve smoked, you can still improve your health and odds of living longer by making one firm decision: Now’s the time to quit.

References:

[1] Association of long-term, low-intensity smoking with all-cause and cause-specific mortality in the National Institutes of Health-AARP Diet and Health Study. Inoue-Choi M, Liao LM, Reyes-Guzman C, Hartge P, Caporaso N, Freedman ND. JAMA Intern Med. 2016 Dec 5. [Epub ahead of print].

[2] Cigarette smoking and mortality in adults aged 70 years and older: Results From the NIH-AARP Cohort. Nash SH, Liao LM, Harris TB, Freedman ND. Am J Prev Med. 2016 Nov 22. pii: S0749-3797(16)30517-7.

Links:

NIH-AARP Diet and Health Study

smokefree.gov

Maki Inoue-Choi (National Cancer Institute, Rockville, MD)

NIH Support: National Cancer Institute; National Institute on Aging