Obesity; it has been linked to increased risk of heart disease, type 2 diabetes and even some cancers. Now, for the first time, researchers claim that obesity can also speed up aging of the liver.
The research team - including first author Steve Horvath, a professor of human genetics at the David Geffen School of Medicine at the University of California-Los Angeles - says their study could explain why obese individuals often experience early onset of some age-related diseases, such as diabetes and liver cancer.
They publish their findings in the Proceedings of the National Academy of Sciences (PNAS).
Researchers have long suspected that obesity accelerates aging in humans. According to Horvath, however, it has been impossible to prove such a theory.
But last year, Horvath developed an "aging clock" - a time-keeping tool that he says can accurately indicate the biological age of an array of human organs, tissues and cells by monitoring the DNA methylation process.
Using this tool, Horvath and colleagues found a link between obesity and accelerated liver aging.
Liver ages by 3 years for every 10 additional BMI units
To reach their findings, the researchers assessed almost 1,200 human tissue samples, of which 140 were liver samples. The team also noted the weight, height and body mass index (BMI) of individuals from which the samples were taken.
They found that for every 10 additional body mass index (BMI) units, the biological age of the liver increased by 3.3 years. They explain, for example, that a woman who is 5 feet 5 inches and weighs 140 pounds would have a BMI of 23.3. A woman of the same height who weighs 200 pounds would have a BMI of 33.3, meaning her liver would be more than 3 years older than that of the woman with the lower BMI.
"This does not sound like a lot, but it is actually a very strong effect," says Horvath. "For some people, the age acceleration due to obesity will be much more severe, even up to 10 years older."
The team points out that rapid weight loss through bariatric surgery did not reverse short-term accelerated aging of the liver.
No link was found between obesity and advanced biological aging of fat, muscle or blood tissue.
Commenting on their findings, the researchers say:
"The increased epigenetic age of liver tissue in obese individuals should provide insights into common liver-related comorbidities of obesity, such as insulin resistance and liver cancer.
These findings support the hypothesis that obesity is associated with accelerated aging effects and stresses once more the importance of maintaining a healthy weight."
According to the Centers for Disease Control and Prevention (CDC), more than a third of American adults are obese. Horvath notes that given the obesity epidemic in the Western world, their findings are highly relevant to the health of the general public.
In future research, the team wants to find out if there is a way the biological aging of the liver can be prevented in obese individuals, therefore reducing the risk of liver cancer and diabetes. To do this, they plan to create models that enable them to determine the molecular mechanisms underlying advanced liver aging.
Medical News Today recently reported on a study by researchers from Washington State University claiming that eating a Granny Smith apple once a day could protect against obesity.