The hormone leptin controls appetite
High levels of a hormone that controls appetite appear to be linked to a reduced risk of developing Alzheimer's disease, US research suggests.
The 12-year-study of 200 volunteers found those with the lowest levels of leptin were more likely to develop the disease than those with the highest.
The JAMA study builds on work that links low leptin levels to the brain plaques found in Alzheimer's patients.
The hope is leptin could eventually be used as both a marker and a treatment.
The hormone leptin is produced by fat cells and tells the brain that the body is full and so reduces appetite. It has long been touted as a potential weapon in treating obesity.
But there is growing evidence that the hormone also benefits brain function.
Research on mice - conducted to establish why obese patients with diabetes often have long-term memory problems - found those who received doses of leptin were far more adept at negotiating their way through a maze.
The latest research, carried out at Boston University Medical Center, involved regular brain scans on 198 older volunteers over a 12-year period.
A quarter of those with the lowest levels of leptin went on to develop Alzheimer's disease, compared with 6% of those with the highest levels.
"If our findings our confirmed by others, leptin levels in older adults may serve as one of several possible biomarkers for healthy brain ageing and, more importantly, may open new pathways for possible preventive and therapeutic intervention."
Rebecca Wood, chief executive of the Alzheimer's Research Trust, said: "Previous studies have shown that obesity in mid-life is associated with an increased risk of dementia, but this new research suggests that leptin might have a role to play.
"There is evidence that leptin has functions in the brain - further studies in this area could lead to the possibility that this hormone plays a role in new treatments for Alzheimer's."
Susanne Sorensen, head of research at the Alzheimer's Society, described the research as "important".
She said: "Further investigation is now needed to understand this relationship.
"This could move us closer to understanding the causes of the disease and provide vital information for drug development."
There are currently 700,000 people in the UK living with dementia.