Research Shows Those Who Are Fit Fight Drugs Better

Research by a Davidson College neuroscientist and students demonstrates that the benefits of regular exercise include a lowered tendency to become addicted to illegal drugs.

The online version of the journal Drug and Alcohol Dependence published this week the results of the study by Associate Professor Mark A. Smith that shows that exercise can help prevent drug addiction.

Smith said his research provides scientific validity for a long-standing suspicion among drug abuse researchers that exercise plays a role in helping people avoid and overcome drug addiction. “We’ve known that individuals who engage in exercise have lower rates of substance abuse,” said Smith. “But there were previously no data that showed a cause and effect relationship.”

Smith’s findings take on added importance in light of a newly announced initiative by the National Institute of Drug Abuse (NIDA) to support research on exercise and drug abuse. Recent studies show that about 20 million Americans age 12 and older (about 8.3% of the population) have used an illicit drug in the past month. Speaking at a NIDA conference June 4-5, director Dr. Nora Volkow committed $4 million for studies about the effect of exercise on drug use. Smith’s Davidson research was not published until after the NIDA conference.

He did, however, present his findings in a poster to enthusiastic researchers attending a conference of the College on the Problems of Drug Dependence in mid-June. “I’ve never had so many people interested in my research,” he said. “I felt like a rock star. At the end of the two-hour session I had to ask people to contact me later by email so we could all go hear the next speaker.”

Smith worked for about two years on the study with three Davidson student research assistants— Karl Schmidt, Jordan Iordanou and Martina Mustroph—all of whom graduated in May. They compared the tendency to self-administer cocaine between two groups of rats. One group of rats lived in laboratory cages equipped with a running wheel, and the other group lived in a standard cage with no wheel. During six weeks, the rats in the wheel cages increased their running to about 10 kilometers per day, while those without wheels got no exercise at all.

At the end of six weeks, all the rats were connected to an infusion pump that would provide a dose of cocaine if they pushed a lever in their cage. However, the number of pushes necessary to deliver a dose increased geometrically for each subsequent dose.

The researchers found that the fit rats abandoned the task when 70 lever presses were required for a cocaine infusion. However, sedentary rats kept pushing the lever even when 250 lever presses were required for an infusion. In addition, the rats that ran the most on the wheel abandoned the task at a lower number of pushes than their fellow exercising rats.

“We concluded that aerobic exercise reduces the rewarding effects of cocaine, and probably also has protective effects against cocaine abuse.” Smith said. “That shows me that in the real world, exercise can be an effective intervention in drug abuse prevention and treatment programs. As a treatment, it’s widely available, easy to execute, inexpensive, and feasible for use in diverse patient populations. In addition, its principle side effects are all positive—weight loss, lower blood pressure, and increased confidence and self-esteem.”

Smith said exercise works because both exercise and illicit drugs prompt the same release in the brain of the euphoria-inducing protein, dopamine. Long-term exercise alters the number of dopamine receptors in the brain, meaning that drugs then have less of a euphoric effect.

Smith said he expects other researchers to begin working on exercise studies with human patients. His subsequent project at Davidson, however, will determine whether exercise can help mitigate the effects of relapse to drug use among rats.

Smith and student researchers Katie Walker ’10 and Kathryn Cole ’09 are beginning by having the entire group of rats self-administer cocaine. The drugs are then stopped, with one group abstaining in wheel-equipped cages and the other in standard cages with no wheel. After a period of time, they will reintroduce the self-administration of cocaine to determine whether exercise lessens the relapse rate in those rats that were able to exercise. The study is funded by grants from the National Institute on Drug Abuse, the Davidson Research Initiative, and Howard Hughes Medical Institute.

Smith believes exercise can prevent not only addiction to cocaine, but other drugs as well since they all affect dopamine levels. In the future, he plans to conduct a similar study at Davidson with heroin.

Smith is enthusiastic about the contribution of his study. He said, “Exercise has long been known to produce positive cardiovascular effects. We’re now also finding that it has positive psychological effects as well, in the treatment and prevention of drug abuse, depression, and anxiety disorders. I think there’s even more and we’re just beginning to scratch the surface.”

Smith, a 1992 magna cum laude graduate of Lenoir Rhyne College, earned his Ph.D. in experimental and biological psychology at UNC before joining the faculty at Davidson in 1998. He has published more than 25 articles in journals, most of which concern the neurological effects of illegal drugs. He teaches courses in general psychology, learning and behavioral pharmacology, and has mentored 15 students in their thesis work.

Davidson is a highly selective independent liberal arts college for 1,700 students located 20 minutes north of Charlotte in Davidson, N.C. Since its establishment in 1837 by Presbyterians, the college has graduated 23 Rhodes Scholars and is consistently regarded as one of the top liberal arts colleges in the country. Through The Davidson Trust, the college became the first liberal arts institution in the nation to replace loans with grants in all financial aid packages, giving all students the opportunity to graduate debt-free. Davidson competes in NCAA athletics at the Division I level, and a longstanding Honor Code is central to student life at the college.

Source: Davidson College