Adult smokers are twice as likely as former smokers, and four times as likely as people who never smoked, to have poor oral health, HealthDay reports. The findings come from the Centers for Disease Control and Prevention (CDC).

The CDC found 16 percent of smokers had poor oral health, compared with 8 percent of former smokers, and 4 percent of people who never smoked. The study also found 35 percent of current smokers had three or more oral health problems, compared with 24 percent of former smokers, and 16 percent of people who never smoked.

Current smokers were about twice as likely as former smokers and people who never smoked to have not visited the dentist in more than five years, or to have never visited one.

Most people with an oral health problem who had not seen a dentist in the past six months cited cost as the reason. The study found 56 percent of current smokers could not afford treatment or did not have insurance, compared with 36 percent of former smokers and 35 percent of people who never smoked.

There is strong evidence for an association between tobacco use and oral disease, the CDC notes. Tobacco use is a risk factor for oral cancers, periodontal diseases, and cavities, among other health conditions. “Oral health problems may be early warning signs of other medical problems such as diabetes, HIV, heart disease, or stroke,” the report states.