The study of 16 young men who were habitual spit tobacco users measured their responses 30 minutes after dipping snuff.
These readings were compared with measurements from another session involving the same participants after they had used a placebo product that was similar in taste, color and texture but did not contain tobacco or nicotine. The study was randomized and double-blinded; neither the researchers nor the subjects were told when they were taking the placebo and when they were using the tobacco product.
After snuff use, heart rate increased by about 15 beats per minute (25 percent), systolic blood pressure went up by 12 mmHg (10 percent), and measurements of adrenalin in the bloodstream increased by more than 50 percent.
"These results suggest a very significant excitatory effect of substances contained in spit tobacco on the part of the nervous system regulating the heart and blood vessels," says Virend Somers, M.D., Ph.D., the Mayo Clinic cardiologist who led the study. "Although we did anticipate some increase in blood pressure, we were surprised at the magnitude of the increase, as well as the very striking increases in heart rate and plasma epinephrine, or adrenalin. We anticipated that since these individuals were young and healthy and were accustomed to using spit tobacco, that any responses that we measured would be blunted. This makes the degree of increases even more noteworthy."
Robert Wolk, M.D., Ph.D., lead author on this study, noted that these results have implications both for long-term users and for individuals with established heart disease.
"The degree of speeding up of heart rate and increase in blood pressure, as well the increase in adrenalin (epinephrine) levels, suggest that if similar changes occur in people with established heart disease, who use spit tobacco, there may be reason to expect adverse consequences," Dr. Wolk says.
More than five million adults – and more than 750,000 adolescents – use smokeless tobacco in the United States. Snuff use is increasing, especially in young males who participate in athletics. Its cardiovascular effects are not as clear or well understood as those of cigarettes, partly because fewer studies have been done, and partly because many spit tobacco users are relatively young and the bad effects may not be apparent unless use continues for prolonged periods.
By placing electrodes into the sympathetic nerves of the participants, the researchers also obtained a window on the message from the brain to the blood vessels on a moment-by-moment basis.
Normally, when blood pressure is increased by an external substance, the body seeks to protect the cardiovascular system by decreasing heart rate and dilating the blood vessels. It does this by "shutting down" the sympathetic nervous system, so that heart rate is slower, and the widening of blood vessels starts to bring blood pressure down.
The researchers demonstrated this by giving another group of subjects an intravenous medication, phenylephrine, to raise blood pressure about as much as they saw when spit tobacco was used. In response, those subjects' heart rates decreased by more than 10 beats a minute and the activity of the sympathetic nervous system went down to very low levels.
"This is an example of how the body tries to protect itself from the higher blood pressures," Dr. Somers explains. "However, when the blood pressure is raised by spit tobacco, the heart rate actually speeds up dramatically and there is no decrease in the sympathetic nervous system activity. This tells us that the normal protective mechanisms which help dampen down spikes in blood pressure are blunted when using spit tobacco.
"Spit tobacco is a very potent cause of acute increases in blood pressure, heart rate, and adrenalin levels," Dr. Somers concludes. "Since many athletes, who are already under a fair amount of stress in competitive situations, also use spit tobacco, the blood pressure and heart rate increases need to be recognized and understood. And since spit tobacco not only raises blood pressure but also blunts the body's normal defense response to blood pressure increases, long-term dipping would seem likely to increase the risk of cardiovascular disease."