A study funded by the National Institutes of Health has uncovered why cigarette smokers often die from cardiovascular disease: nicotine promotes insulin resistance (referred to as prediabetes), a condition considered to be a risk factor for cardiovascular disease. "This may explain why cigarette smokers have a high cardiovascular death rate, even though smoking causes weight loss, which should protect against heart disease," says study lead author Theodore Friedman, M.D., Ph.D., chief of the endocrinology division at Charles Drew University of Medicine and Science in Los Angeles.

Past studies have shown that smokers tend to become insulin resistant, and to compensate, their blood sugar levels rise to levels higher than normal, but not to full-blown diabetic levels. Other studies have also shown that nicotine and cigarette smoking cause the levels of the stress hormone, cortisol, to rise. "As cortisol excess is known to induce insulin resistance, it has been suggested that glucocorticoids, such as cortisol, are the missing link between cigarette smoking and insulin resistance," says Dr. Friedman.

In conducting the study, researchers from Charles Drew University and Western University of Health Sciences in Pomona, CA injected 24 adult mice with nicotine twice a day for two weeks. They found that the nicotine-injected mice ate less, lost weight and had less fat than the control group. Yet despite losing weight, they still developed prediabetes and had high levels of cortisol in their blood and tissues. After being treated with mecamylamine, a nicotine antagonist that blunts the action of nicotine, they showed some improvement. "Our results suggest that reducing tissue glucocorticoid levels or decreasing insulin resistance may reduce the heart disease seen in smokers," says Dr. Friedman. However, noting that current nicotine antagonists are not specific enough to completely block the effects of nicotine or have too many side effects, he says that better drugs are needed and anticipates that in the future "there will be drugs to specifically block the effect of nicotine on glucocorticoids and insulin resistance."

News Release: Nicotine induces prediabetes, likely contributes to high prevalence of heart disease in smokers http://www.newswise.com/articles/view/553252/ July 11, 2009