Nicotine is an alkaloid present in tobacco products at concentrations between 1 and 3 percent in the United States. It is also used medically, most often for replacement therapy for people trying to quit the use of tobacco products. Nicotine is rapidly absorbed into the bloodstream after oral, dermal and inhalation exposure. Although smoking increases the risk for developing type 2 diabetes, a disease in which high blood glucose levels are the primary feature, it is not clear whether nicotine is the chemical in cigarettes that causes the increased risk. Nicotine has been shown to have several effects on glucose metabolism in animals, but none have been consistently observed in human studies.
Nicotine
Nicotine affects many chemicals in the brain that act as messengers, most notably, dopamine. It also stimulates the adrenal glands to produce adrenaline. The prevailing theory of how nicotine causes an increase in blood glucose levels, or hyperglycemia, is that nicotine increases the release of adrenaline, which then increases liver production of glucose.
Blood Glucose Levels
Glucose is the major nutrient used for energy production in the body. Blood glucose levels are primarily maintained by the hormone insulin, but are also affected by growth hormone, cortisol, glucagon and adrenaline, among other hormones. Blood glucose levels are maintained in a narrow range because high levels of glucose cause acute and chronic organ damage and low levels acutely affect brain functioning. Nicotine has been found in some human studies to transiently elevate blood glucose levels, but in others it had no effect.
A1C Levels
A1C levels are a measurement of average blood glucose concentrations in a person over a two- to three-month time period. A study published in the May 1989 issue of the “Journal of Family Practice” reported that smokers had an average blood glucose level that was 20 percent higher than that of nonsmokers. Another study in a 2002 issue of the “Journal of Investigational Medicine” found no effect of cigarette smoking on average blood glucose levels in type 2 diabetic patients. Studies have not been conducted that have evaluated the effects of nicotine exposure alone on average blood glucose concentrations.
Nicotine and Diabetes
A review in “Diabetes Care” concludes that smoking increases the risk for developing type 2 diabetes and increases the risk of cardiovascular disease and nerve and kidney damage in type 2 diabetics. The evidence is substantial that smoking increases the risk of type 2 diabetes between two- and three-fold, but it has not been demonstrated that nicotine is the causative agent. A major problem with studies that evaluate the effects of cigarette smoking on the risk of type 2 diabetes is that nicotine addiction is more prevalent in people with a sedentary lifestyle, which is also a risk factor for type 2 diabetes.
Prenatal Nicotine Exposure
Children of mothers who smoked during their pregnancy are at greater risk for developing impaired glucose management and type 2 diabetes. Nicotine, either from smoking or replacement therapies, crosses the placenta and is also detectable in breast milk. A study in the “Journal of Endocrinology” found that rats exposed to nicotine in utero had impaired glucose management and a decreased number of insulin-secreting cells.
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