Smokers who like their early morning cigarette has a much greater risk of developing lung cancer according to US scientists.

The new study, led by Dr. Joshua Muscat of Penn State College of Medicine has discovered that smokers who smoke within 30 minutes of waking up are 1.79 times as likely to develop head, neck and lung cancer as those who wait an hour after waking up to smoke.

The two studies, which will be published today in the journal Cancer, had data collected from medical centers in New York City between 1977 and 1999. Patients with cancer were matched with control subjects and asked questions about their smoking habits.

The researchers found that those who smoked their first cigarette of the day within 31 to 60 minutes of waking up were 1.31 times more likely to develop lung cancer than those who smoked after an hour. Smokers who lit up within 30 minutes had 1.79 times increased risk of developing cancer than those smokers who waited an hour before smoking.

A second analysis of head and neck cancer cases showed similar findings. Patients who smoked within 30 minutes and 60 minutes after waking up were 1.59 and 1.42 times more likely to develop head and neck cancer respectively when compared to those who waiter an hour or more.

Muscat says that the studies' results do not suggest that smokers can avoid developing lung cancer by delaying their first cigarette smoking time.

"It's not a voluntary thing. People smoke because they are highly dependent," says Muscat.

"They really don't have the option of waiting, they wake up and crave cigarettes and they smoke, it's not a behaviour that is modifiable."

"We think the early morning smokers are more nicotine dependent and unlikely to change their smoking habits."

The study only proves that time to first cigarette is a main measure of strength of addiction according to Professor Simon Chapman, Professor of Public Health at University of Sydney.

"So all this study may be saying is that those most addicted (who tend to smoke more and more intensively) are most are most at risk for later disease," said Professor Chapman, who was not involved in the studies, according to a report in The Conversation.edu.