12 May Drug Abuse and Obesity: What Do They Have in Common?
Two of the most challenging health problems in America today are drug abuse and obesity. The search for ways to unlock the secrets of both types of addiction may have just gotten a boost. Results of new research, funded by the National Institute on Drug Abuse (NIDA), a component of the National Institutes of Health (NIH), show that some of the same brain mechanisms that fuel drug addiction in humans also accompany the emergence of compulsive eating behaviors and development of obesity in animals.
About the Study
The study, “Dopamine D2 receptors in addiction-like reward dysfunction and compulsive eating in obese rats,” conducted by researchers at the Scripps Research Institute, Jupiter, Florida, was released in the online version of Nature Neuroscience (http://www.nature.com/neuro/journal/vaop/ncurrent/full/nn.2519.html) March 28, 2010, and will appear in the May 2010 print issue. When researchers gave rats unlimited access to high-fat food in varying levels, they found that unrestricted availability alone can trigger addiction-like responses in the brain, leading to compulsive eating behaviors and the onset of obesity.
Both obesity and drug addiction, say researchers, have been linked to a dysfunction in the brain’s reward system.
Overconsumption in both cases can trigger a gradual increase in the reward threshold. This results in the requirement of more and more palatable high-fat food or reinforcing drug to satisfy the cravings over time.
Dr. Nora D. Volkow, director of NIDA, commenting in a press release on the study (http://www.eurekalert.org/pub_releases/2010-03/niod-cmo032610.php) said, “This research opens the door for us to apply some of the knowledge we have gathered about drug addiction to the study of overeating and obesity.”
The study results appear to support the idea that type 2 dopamine receptors (D2DR) – brain receptors that have been shown to play a key role in addiction – also play a key role in the rats’ heightened response to food. As the rats became obese, levels of D2DR in the brain’s reward circuit decreased. This drop in D2DR, say researchers, is similar to what happens in humans addicted to drugs like heroin or cocaine.
Paul J. Kenny, one of the study’s co-authors and an associate professor at Scripps Jupiter, Florida research facility, points out the potential implications. “It is possible that drugs developed to treat addiction may also benefit people who are habitual overeaters.”
Paul Johnson, co-author and graduate student in the department of molecular therapeutics, has this to say: “Hopefully, this will change the way people think about eating. It demonstrates how just the availability of food can trigger overconsumption and obesity.”
U.S. Obesity Rates Still High
According to an Associated Press story (http://readingeagle.com/article.aspx?id=186226), government data released in January 2010 from the period 2007-2008 show that obesity levels in the U.S. have leveled off from earlier increases, but the rates are still alarming. Two reports, from the Centers for Disease Control and Prevention (CDC), show that the vast majority of adults in this country are overweight, 34 percent of adults are obese and 17 percent of children are obese. In addition, 10 percent of babies and toddlers are dangerously heavy.
A USA Today story (http://www.usatoday.com/news/health/weightloss/2010-01-13-obesity-rates_N.htm?loc=interstitialskip) on the data indicates that 73 million adults (34 percent) were obese in 2008, compared to 31 percent in 1999. Obese means that they were roughly 30 or more pounds over a healthy weight. The USA Today story also highlighted the following:
• Obesity will cost U.S. health care $344 billion a year.
• The hazards of obesity now rival those of smoking.
• Extreme obesity can shorten lifespan by 12 years.
Obesity is the second leading cause of preventable death, right behind the number one cause, smoking. Obesity is associated with numerous significant health problems, including heart disease, high blood pressure, diabetes, stroke, osteoarthritis, sleep apnea, premature death, and decreased quality of life.
Substance Abuse and Addiction
Drug addiction (substance abuse) is a chronic relapsing brain disease, and the discovery of effective medications to treat addictive disorders is a high priority in addiction research. According to NIDA, it is a complex illness, characterized by intense, sometimes uncontrollable, drug craving along with compulsive drug seeking and use that persist even in the face of devastating and potentially life-threatening circumstances.
While the path to addiction begins with the act of taking drugs, over time the person’s ability to choose not to do so becomes compromised, to the point where they no longer have any control over their actions. Thus, the seeking and use of the drug becomes compulsive. Such behavior is the result of prolonged drug exposure on brain functioning. Drug addiction affects many different brain pathways or circuits. These include those involved in reward and motivation, learning and memory, and inhibitory control over behavior.
Some individuals are more vulnerable to addiction than others, with contributing factors that include genetic makeup, age at exposure to addictive drugs, other environmental influences, and the interaction of multiple factors.
In 2008, according to the National Survey on Drug Use and Health (NSDUH) (http://www.oas.samhsa.gov/nsduhLatest.htm), 22.2 million Americans aged 12 and older were classified with substance dependence or abuse in the past year. That’s 8.9 percent of the population aged 12 and older. Of this number, 3.1 million were classified with dependence upon or abuse of both alcohol and illicit drugs, while 3.9 million were dependent upon or abused illicit drugs but not alcohol, and 15.2 million abused or were dependent on or abused alcohol but not illicit drugs.
Marijuana was the illicit drug with the highest rate of past-year dependence or abuse in 2008, followed by pain relievers and cocaine. In 2008, of the 7.0 million persons aged 12 or older classified with dependence on or abuse of illicit drugs, 4.2 million were dependent on or abused marijuana or hashish, 1.7 million for pain relievers, and 1.4 million for cocaine. These were followed by tranquilizers (451,000), hallucinogens (358,000), stimulants (351,000), heroin (282,000), inhalants (175,000), and sedatives (126,000).
Showing the magnitude of the problem of substance abuse and addiction, in 2008, some 23.1 million persons aged 12 or older needed treatment for an illicit drug or alcohol use problem – but only 2.3 million actually received treatment at a specialized treatment facility. That left 20.8 million persons who needed treatment untreated.
Seeking and Using Behavior Common to Both
Substance abuse and obesity have something else in common: seeking and using behavior. It is well known that drug abusers and addicts engage in drug seeking and using despite negative consequences, driven by insatiable urges and cravings over which they no longer have any control. Persons who are obese exhibit similar behavior. They often state that they want to cut down or to stay on an eating regimen, but are unable to keep from overeating – notwithstanding the considerable medical risks.
The more they use (drugs, overeating), the more the addicts crave and desire to continue the behavior, to use more, and to do so more frequently. They build up a tolerance, requiring more and more of the drug (or food) to reach the same level of reward (satisfaction or high). Withdrawal from the drug (or food) causes symptoms ranging from mild to moderate to severe. As soon as the drugs are removed from the body, the cravings resurface, causing the user to once again resort to the drug seeking and using behavior. Often medication or treatment in the form of intense counseling is the only way to stop the vicious addiction cycle and downward spiral of such abuse.
Hope for the Future
Researchers continue to study the brain mechanisms that may hold the key to addictive behavior – whether that behavior is substance abuse or obesity. What science has learned so far is tantalizing and sometimes contradictory. Different drugs of abuse may be rendered impotent by different types of medications, but there isn’t a single medication that will work for all addictive behaviors. There are many different types of receptors in the brain that drugs of abuse work on, or attach themselves to. Finding the key to unlock this intricate maze of neurotransmitter signaling and reward pathway response is one of the great mysteries. But it’s a challenge that researchers are pursuing with utmost zeal. Given that the problems of addiction and addictive behavior aren’t going away any time soon, the hope is that the furious pace of research will, at some point, yield promising results.
One thing is certain. The field of addiction research has become an exciting arena. As time goes on, more neurobiological connections to addiction are discovered. With the brain’s secrets gradually being revealed, there’s greater likelihood of some major advances in the area of prevention and treatment. Although it’s still early, and getting any drugs to market will take years of FDA testing and approvals, the promise is there and the long-term outlook is positive.
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