WASHINGTON, Dec. 7 (Xinhua) -- It's not safe to smoke even at a small number of cigarettes per day, as it still has substantial negative health effects, according to a recent study done by researchers in the United States.

The National Cancer Institute revealed on Monday that its researchers found people who consistently smoked an average of less than one cigarette on a daily basis over their lifetime had a 64 percent higher risk of earlier death than nonsmokers.

For those who smoked one to 10 cigarettes a day, the increased risk rate could reach as high as 87 percent.

Higher lung cancer mortality has also been associated with smokers among the study participants. Those who averaged less than one cigarette per day were eight times more likely to die from lung cancer than nonsmokers. The risk was nearly 12 times higher for those who consumed one to 10 cigarettes daily.

The study also observed that smokers were more likely to die from respiratory and cardiovascular diseases than those who did not take a puff at all.

For those former smokers, risk fell with earlier age at quitting.

"The results of this study support health warnings that there is no safe level of exposure to tobacco smoke," said Maki Inoue-Choi, the lead author of the study.

Data of around 290,000 adults, aged 59 to 82, were analyzed in the research. The participants were asked to recall their smoking behavior over past decades.