How Old Is That Polar Bear? The Answer Is in Its Blood.

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Susannah Woodruff, a wildlife biologist at the U.S. Fish and Wildlife Service, is relieved to no longer have to extract teeth from polar bears to determine their age. Dr. Woodruff monitors the population of bears in Alaska and needs to know their ages to estimate how many will soon die of old age and how many will enter their reproductive years. Traditionally, the only reliable method of determining a polar bear’s age was by inspecting its growth rings. However, Dr. Woodruff and her colleagues have started using a method called the epigenetic clock, which analyzes chemical tags on the bears’ DNA to estimate their ages. This method provides an estimate within a year of the bears’ true ages, making it more accurate than examining teeth.

The implications of the epigenetic clock extend beyond polar bears. A recent study published in the journal Nature Aging revealed that epigenetic clocks exist in 185 different species of mammals, including humans. The study suggests that the epigenetic clock begins ticking shortly after fertilization and determines the lifespan of a species. It is surprising that a single mathematical formula can measure aging in such diverse species as bats and whales.

The epigenetic clock relies on methyl groups, which are small molecules bound to DNA. When cells divide, the DNA in the new cells typically has the same pattern of methyl groups. Scientists have known about methylation for decades but are still trying to understand its purpose. It is believed to be involved in either keeping genes active or turning them off. Dr. Steve Horvath, who led the new studies, used methylation data from thousands of human cells to train a computer to predict a person’s age based on their DNA’s methylation pattern. This study found that certain factors like smoking, obesity, and drinking can accelerate the epigenetic clock, increasing the risk of death.

Although scientists still have much to learn about epigenetic clocks, Dr. Horvath and his colleagues are working to understand the underlying molecular mechanisms. They trained a computer to create a new clock that could predict the age of animals based on a single epigenetic pattern across species. By looking at less than 1,000 spots in mammal DNA, the clock was able to accurately estimate the ages of 185 different species. This breakthrough could revolutionize the field, allowing biologists to easily estimate the age of wild animals and potentially uncover the reasons why all mammals, including humans, age.

The early success of epigenetic clocks has also sparked interest in the field and led to the creation of companies offering to estimate a person’s biological age using this method. However, these tests have not been approved by the FDA, and some experts are skeptical of their value. Dr. Horvath hopes that epigenetic clocks will eventually lead to treatments that slow down the aging process. By using the clock to compare mice on a restricted diet to those on a normal diet, he and his colleagues discovered that the clock could be turned back by four months in the mice on a restricted diet. This research suggests that a treatment mimicking calorie restriction could potentially slow down aging in humans.

While the epigenetic clock offers promising possibilities, Dr. Horvath doubts that it will extend human lifespan beyond the current maximum of around 120 years. He believes that the maximum lifespan is determined during development and cannot be altered. Despite this limitation, the epigenetic clock is a significant breakthrough that could have a profound impact on aging research and potentially lead to the development of anti-aging treatments.

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