People who smoke soon after getting up in the morning are more likely to develop cancer than those who light up later in the day.
In a study of 7,610 smokers, US researchers found that smoking within the first 30 minutes after waking almost doubled the already high risk of developing lung cancer.
Smokers may inhale more smoke into the lungs earlier in the day compared with those who wait longer before having their first cigarette.
“Time to first cigarette” has a huge impact on risk of cancer: having a cigarette within 30 minutes of waking up meant that the subjects were up to 79 per cent more likely to develop cancer than those who waited at least an hour before smoking.
Cancer Research UK's Professor Robert West said: “Smokers who light up soon after waking tend to smoke each cigarette more intensively.
“So the most likely explanation of this finding is that the sooner a smoker lights up, the more smoke is taken into the lungs, and the higher the level of exposure to cancer causing chemicals”.