A new study has shed light on why smokers are at an increased of suffering heart disease and stroke.
The research team from Charles Drew University of Medicine and Science in Los Angeles and Western University of Health Sciences in Pomona has revealed that nicotine in cigarettes promotes insulin resistance, a pre-diabetic condition that raises blood sugar levels higher than normal.
And people with pre-diabetes are known to be at higher risk of developing cardiovascular disease.
Lead researcher Dr Theodore Friedman, chief of the endocrinology division at Charles Drew University said the findings help explain a "paradox" that links smoking to heart disease.
He said smokers experience a high degree of cardiovascular deaths.
"This is surprising considering both smoking and nicotine may cause weight loss and weight loss should protect against cardiovascular disease," Friedman added.
During the study, the researchers looked at the effects of twice-daily injections of nicotine on 24 adult mice over two weeks.
They found that nicotine-injected mice ate less food, lost weight and had less fat than control mice that received injections without nicotine.
"Our results in mice show that nicotine administration leads to both weight loss and decreased food intake," Friedman said.
"Mice exposed to nicotine have less fat. In spite of this, mice have abnormal glucose tolerance and are insulin resistant (pre-diabetes)," he added.
The researchers found that the mice receiving nicotine developed pre-diabetes and also had high levels of the stress hormone cortisol, which increases blood pressure and blood sugar.
The study's authors were able to partially reverse the harmful effects of pre-diabetes by treating the mice with a drug that blunts the action of nicotine.
"Our results suggest that decreasing insulin resistance may reduce the heart disease seen in smokers," Friedman said.
"We anticipate that in the future there will be drugs to specifically block the effect of nicotine on insulin resistance," he added.
The findings were presented at The Endocrine Society's 91st annual meeting in Washington, D.C.