They have much higher levels of nicotine and other toxins in the body than people lighting up at least one hour later after getting up. It was found that the effect is independent of other habits associated with smoking.
It is known that smoking increases the risk of various cancers.
Nicotine breaks down into cotinine - a molecule associated with a risk of developing the disease, experts explain.
Researchers from the Medical College of Pennsylvania explore why only some smokers develop the disease. They examined the relationship between the time of the first cigarette after waking and cancer, irrespective of the duration and frequency of habit.
According to the research team there is a close connection between the reception of nicotine and the formation of cancer cells.
The study includes regular smokers - 4,775 people with lung cancer and a control group of 2,835 people.
It turns out that people lighting up to 30 minutes after waking in the morning is 1, 8 times more likely to develop lung cancer than those who begin to smoke 60 minutes after getting up.
The study was published in the Journal Cancer.