The brain link: researchers have discovered an amazing connection between how the brain is involved in obesity and drug addiction
Science World, May 9, 2005
As someone who sees adolescents every day, you are no doubt concerned that the number of teens battling health-threatening weight problems is growing. What you may not realize is that NIDA researchers are discovering fascinating connections between obesity and another key teen health issue: drug addiction.
Amazingly, drug abusers and those who suffer from obesity appear to have a similarity in brain chemistry that seems partly responsible for these compulsive behaviors.
The common link is the neurotransmitter dopamine, the brain chemical responsible for stimulating feelings of pleasure. This year's fourth and final installment of Heads Up discusses this link, as well as obesity research and treatment. Like all of the articles in the series this year, this one reinforces our understanding of addiction as a brain disease--a disease that can be treated, understood, and, most important, prevented.
Learning about the seemingly unlikely link between obesity and drug addiction will give students an intricate view of how science works. It will also teach them that researchers can never know for sure where the facts will lead them. NIDA-sponsored scientists started out doing work on drug addiction but soon found themselves researching obesity, as well.
Thank you for taking time to share the lessons of Heads Up with your students. You have helped set the stage for a healthier, smarter, and drug-free generation of young adults.
Nora D. Volkow, M.D.
Director of NIDA
Ask experts to name the biggest health threats for teens today, and these two answers will rise to the top: obesity and drug addiction.
Are you surprised by the first answer? You shouldn't be.
More and more teens weigh far too much, and the problem is growing. It's no joke. Check out these numbers: 16 percent of young people between the ages of 12 and 19 are overweight, according to a 1999-2002 federal study by the Centers for Disease Control and Prevention. That's more than triple what the rate was between 1976 and 1980. The same study revealed that an additional 15 percent of teens are at risk of becoming overweight.
What's so bad about being overweight or obese? For starters, it can cause diabetes, a life-shortening disease in which the body loses its ability to metabolize sugar. It can also lead to asthma and can cause heart disease. Most obese people just aren't healthy, overall.
HEADS UP: A WILD CONNECTION
What do you think? Could the health threats of drug addiction and obesity be connected? If you're like most people, you probably think, "No way." Well, you--and most people--are wrong!
Think about it. People addicted to drugs and those who suffer from obesity have at least one thing in common. It can be extremely hard for them to stop doing things that they know are harming them. For the drug abuser, it's taking drugs. For the obese person, it's usually excessive eating (although there are other factors as well, as we'll learn). NIDA researchers decided to find out if and how the two disorders could be related. Their amazing new findings indicate that there is a link. If you think back to what you've learned from earlier articles in this series, you can probably guess what the link is. Got it? It's dopamine and the brain.
Researchers are discovering that obesity (like drug addiction) is, at least in part, a brain disease.
HEADS UP: SEE SCIENCE IN ACTION!
How did researchers find the obesity-addiction link? They started by reviewing what they already knew: Dopamine is a brain chemical that stimulates pleasurable feelings. When dopamine binds to special structures in your brain--called D2 receptors--it activates the brain's reward circuits. The end result? You feel good.
For some time now, researchers have known that people who are addicted to alcohol, cocaine, and other drugs tend to have a lower-than-average number of D2 receptors in their brains. That makes sense when you think about it. If you have a shortage of D2 receptors, it's harder for you to feel good. It's harder for dopamine to find a D2 receptor to bind to, so it takes more dopamine for you to feel pleasure. As it happens, most drugs of abuse cause a flood of dopamine in the brain. Taking drugs makes people feel better--in the immediate short term.
Researchers also knew that eating can stimulate the production of dopamine in the brain. Could it be that obese people suffer from a shortage of D2 receptors? They might need to overeat to get feelings of pleasure from food.
Using PET scanners to look inside the brains of obese and non-obese people, researchers Nora Volkow, M.D., who is now the director of NIDA, and Gene-Jack Wang, M.D., found that obese people do have lowered numbers of D2 receptors. In fact, Drs. Volkow and Wang's research at Brookhaven National Laboratory in New York showed that the more obese the person, the lower the number of D2 receptors. "The low number of receptors in obese people might be causing them to overeat," says Dr. Wang. "They might be doing it to compensate for reduced stimulation in their brain's reward circuits."
Dr. Volkow adds, "An individual who has low sensitivity to normal stimuli learns behaviors, such as abusing drugs or overeating, that will activate them."
HEADS UP: ADDICTION MAY CAUSE THE DAMAGE
Just because obese people and drug addicts share a shortage of D2 receptors, does that mean their disorders are caused by the lack of receptors? Not necessarily. It's a classic "chicken-and-egg" question. In other words, which comes first--the addictive behavior or the D2 shortage? Maybe the addictive behavior causes the shortage. Or ... maybe the shortage causes the behavior?
Dr. Wang says an experiment with animals indicates that "having plenty, of D2 receptors does protect against drug abuse and obesity." So, that's some evidence that the D2 shortage causes the behavior. The experiment Dr. Wang is talking about worked like this: Panayotis K. Thanes, a Brookhaven National Laboratory researcher, trained rats to regularly take alcohol, then introduced additional D2 receptors into their brains. As soon as the receptors took hold, the rats' consumption of alcohol decreased. Dr. Wang says researchers have had similar findings involving cocaine and food.
Case closed? Not exactly. Scientists also know that the flood of dopamine in the brain that drug abuse causes can overstimulate the reward pathways--and cause a reduction in D2 receptors in abusers' brains. "In the end, people who become addicted could be much worse off biologically than when they started," says Joseph Frascella, Ph.D., of NIDA'S Division of Treatment Research and Development.
HEADS UP: CHECK OUT THE DIFFERENCES
Of course, there are major differences between drug addiction and obesity. For one, according to Dr. Wang, obesity is not all about the brain. "You have to consider a person's metabolism and other genetic issues," he says. "The brain chemistry is just part of the picture." Dr. Wang adds that it's not accurate to describe an obese person as a "food addict." Rather, one should say that overeating is an "addictive behavior."
Also, drug addiction seems to cause more wide-ranging brain damage than obesity. For example, in people who are addicted to drugs, the drop in D2 receptors is often accompanied by a loss in functioning of the prefrontal cortex--the part of the brain responsible for judgment and impulse control. "In obesity, we didn't see any problems in the prefrontal cortex," says Dr. Wang. This probably explains why obese people, though compulsive when it comes to eating, have more control over their behavior than drug abusers.
HEADS UP: KNOWLEDGE IS POWER
NIDA scientists have made amazing discoveries about the connection between drug addiction and obesity. Although these discoveries are fascinating, can they help people? Yes, definitely. This new information can help people addicted to drugs, obese people, and healthy teens who want to avoid drug addiction or obesity.
How? First, the research shows us that having a healthy supply of D2 receptors in the brain can help stave off addictive behaviors. So, anything that increases D2 levels could be a valuable weapon in the battle against drug abuse and obesity. With this in mind, NIDA researchers are looking to develop new medications.
But is there anything safe and available now that can boost the level of D2 receptors in your brain? "Yes!" says Dr. Wang. "Exercise has been found to increase dopamine release and to raise the number of dopamine receptors," he says. "This suggests that obese people might be able to boost their dopamine response through exercise instead of eating--which is just one more reason to exercise if you are trying to lose weight." He feels that exercise can be helpful for recovering addicts, as well.