Almost two-thirds of people who smoke four or fewer cigarettes a day are addicted to nicotine, a new study finds. The results indicate that lighter smoking is still risky, the researchers say.

The study included more than 6,700 smokers. The researchers found that 85% of daily smokers were addicted to nicotine to some extent, HealthDay reports. The intensity of nicotine addiction increased the more often a person smoked. The study found 35% of people who smoked one to four cigarettes per day were considered to be moderately or severely addicted to nicotine, compared to 74% of those who smoked 21 cigarettes or more each day.

“In the past, some considered that only patients who smoke around 10 cigarettes per day or more were addicted, and I still hear that sometimes,” study co-author Jonathan Foulds of Penn State Cancer Institute said in a news release. “But this study demonstrates that many lighter smokers, even those who do not smoke everyday, can be addicted to cigarettes. It also suggests that we need to be more precise when we ask about cigarette smoking frequency.”