When leptin was first discovered in 1994 by Rockefeller University scientists, the mainstream media hailed it as a breakthrough in obesity research. In studies, the hormone cracked down on appetite and upped fat burning. Researchers were looking at leptin's work in one region of the brain, but leptin also works in other areas of the brain associated with memory and learning. Given that some weight-related medical problems like diabetes have cognitive features, and brain health issues like dementia have weight-related features, scientists have hypothesized that leptin plays a role in both. Early studies demonstrate that high levels of leptin seem to protect against Alzheimer's disease.
Leptin
Leptin is a hormone that is primarily known to help your body achieve homeostasis, or a balance of calories in and calories out. It tells your brain that you're full after you've eaten a meal, and you consequently stop eating because of diminished appetite. In addition, leptin is responsible for dialing up your body's calorie-burning process to maintain your weight and stored energy.
Alzheimer's Disease
Alzheimer's disease is a progressive neurological disorder. Although the early signs are forgetfulness, as the disease advances patients go on to lose their judgment, become disoriented and confused, experience personality changes and gradually lose abilities like speaking, swallowing, maintaining personal hygiene and walking. More than 5 million people in the United States have Alzheimer's disease. According to the Alzheimer's Association, care for Alzheimer's patients in 2010 cost $172 million, including Medicaid and Medicare expenditures and out-of-pocket expenses borne by family members.
The Leptin--Alzheimer's Connection
Researchers have noted that Alzheimer's patients frequently lose weight long before a diagnosis of the disease, leading them to speculate that underneath the neurological disorder was something that had to do with metabolism. At the same time, research has shown that being overweight and obese in your middle years puts you at increased risk of dementia, further underpinning this notion that the systems in your body designed to achieve energy balance may play a role in brain functioning. When the hormone leptin was given to mice, researchers from Boston University discovered that leptin also plays a role in memory, processing and learning. According to findings published in the December 2009 issue of the "Journal of the American Medical Association," another role for leptin may be to help people survive when food is limited, keeping their memory processes alive. In studies appearing in that journal as well as "Peptides," it was found that leptin helped both people and mice remember. In the people study, about 25 percent of those with the lowest levels of leptin developed Alzheimer's, while only 6 percent of those with the highest levels of leptin did. Higher levels of leptin were also associated with bigger brain mass volume. Mice that showed impaired memory were trained on how to traverse a maze through "footshock." Following leptin injections, they remembered which areas to avoid.
Which Came First?
In both research sets, scientists concluded that leptin works in many parts of the brain. The part that regulates food intake and calorie burning is mainly focused in the hypothalamus region, while memory functions take place in the hippocampus region. Leptin, released by fat cells, must cross the blood-brain border to connect with receptors in the brain, but diseases, like obesity, diabetes and now Alzheimer's, can prevent that crossing from happening. Researchers don't know whether something causes leptin levels to drop, leaving you more at risk or if Alzheimer's itself causes a drop in leptin levels. They do know, however, that leptin modulates one of the proteins that are involved in the formation of the disease. It helps to clear up the brain plaques that are a hallmark of Alzheimer's. Scientists think that encouraging people to eat a low-fat diet, along with supplementation with leptin, might one day be a treatment for Alzheimer's patients.
References
- "The FASEB Journal"; Obesity-Related Leptin Regulates Alzheimer's AB; Darius C. Fewlass et al.; December 2004
- "Journal of the American Medical Association"; Association of Plasma Leptin Levels With Incident Alzheimer Disease and MRI Measures of Brain Aging; Wolfgang Lieb et al.; December 16, 2009
- "Neurology Today"; Leptin Levels Tied to Alzheimer Disease; February 18, 2010
- "Peptides"; Effects of Leptin on Memory Processing; Susan A. Farr et al.; June 2006
- "USA Today"; Study: Fat Hormone Leptin May Help Prevent Alzheimer's; Ed Edelson; December 16, 2009
- "Senior Journal"; Hormone that Turns Off Hunger Also Improves Memory; June 15, 2006
