Researchers uncovered an internal biological clock that will help them measure the age of most human tissues. They found that breast tissues age faster than the tissues present in any other parts of the body.

As tissues grow old people begin to age. While this is a natural phenomenon, scientists didn't really understand why it happens. However, in a recent study, researchers from the University of California, Los Angeles, uncovered a biological clock embedded in human genomes that can help them understand why our bodies grow old and if there is any way to prevent or slow this process.

 Previous biological clocks uncovered have been linked to saliva, hormones and telomeres. This is the first time a biological clock that can be used as an age-predictor tool has been discovered. The first discovery made with the help of this tool suggests that different parts of the body anatomy, like the breast tissues, age faster than other parts.

"To fight aging, we first need an objective way of measuring it. Pinpointing a set of biomarkers that keeps time throughout the body has been a four-year challenge," said Steve Horvath, a professor of human genetics at the David Geffen School of Medicine at UCLA and a professor of biostatistics at the UCLA Fielding School of Public Health. "My goal in inventing this age-predictive tool is to help scientists improve their understanding of what speeds up and slows down the human aging process."

To create the age-predictor, Horvath and his team first concentrated on a naturally occurring process called methylation, a chemical modification of one of the four building blocks that make up our DNA. He then accumulated information from nearly 8,000 samples of 51 types of tissue and cells taken from throughout the body. Using this information, he created a chart about how age affects DNA methylation levels from pre-birth through 101 years. He then focused on 335 marks linked to methylation that change with age and are present throughout the body.

To test the tool's effectiveness, Horvath compared a tissue's biological age to its chronological age and found that both readings matched each other.

"It's surprising that one could develop a predictive tool that reliably keeps time across the human anatomy," he said. "My approach really compared apples and oranges, or in this case, very different parts of the body - including brain, heart, lungs, liver, kidney and cartilage."

However, there were a few exceptions like the findings that revealed a woman's breast tissues age faster than tissues of other parts of the body.

"Healthy breast tissue is about two to three years older than the rest of a woman's body," he said. "If a woman has breast cancer, the healthy tissue next to the tumor is an average of 12 years older than the rest of her body."

This finding may explain why breast cancer is the most common form of cancer. Also since tumor tissues were found to be 36 years older than healthy tissues, it could explain why age plays an important role in different forms of cancer across both genders.

The next part of the study involved examining induced pluripotent stem cells, which are adult cells that have been reprogrammed to an embryonic stem cell-like state, enabling them to form any type of cell in the body and continue dividing indefinitely.

"My research shows that all stem cells are newborns," he said. "More importantly, the process of transforming a person's cells into pluripotent stem cells resets the cells' clock to zero."

"The big question is whether the underlying biological clock controls a process that leads to aging," Horvath said. "If so, the clock will become an important biomarker for studying new therapeutic approaches to keeping us young."

The final finding of the study revealed that the speed of this biological clock depends on a person's age. It ticks the fastest in a new-born child and as the child grows from a kid to a teenager. The ticking slows down considerably after a person reaches the age of 20.

The University hopes to conduct future studies to determine whether stopping the body's clock halts the aging process and whether a similar clock exists in mice.