What are biological age tests?

The concept of biological age is typically attributed to Alex Comfort who wrote a paper in 1969 on the subject. However, the biggest advance in the area came in 2013 when Steve Horvath, a professor of human genetics and biostatistics at the University of California, Los Angeles, suggested using a "clock" based on the field of epigenetics.

Epigenetic marks, or reversible changes to DNA, can provide information about how the body is aging. By using DNA from blood, researchers can measure millions of epigenetic marks and use statistical algorithms to determine a person's epigenetic or biological age. Because epigenetic marks can change over time and are affected by lifestyle, stress, and the environment, they can capture aspects of aging that chronological age may not reflect.

Recently, there has been a growing interest in biological age tests, which claim to tell you your "true" biological age and how well your body is functioning. Dozens of companies have marketed biological age tests, with prices ranging from around $30 to over $1,000.

However, none of these direct-to-consumer tests have been approved by FDA, and health experts say they may not be accurate or useful for individual health.

"Expanding access and using more frequent testing to optimize health seems fairly reasonable to me," said Jesse Poganik, an instructor at Harvard Medical School who researches biological aging. But "any claims of accurate, individual-level determination of biological age should be approached with caution."

Why epigenetic clocks aren't designed for individual health

According to Shalev and Apsley, epigenetic clocks are highly informative and helpful tools when studying large groups of people, but they can often provide faulty results at the individual level for several reasons.

1. There are multiple types of epigenetic clocks.

There are dozens of epigenetic clocks, and each was designed with a specific purpose. While some clocks are used to predict a person's age, others are used to predict how quickly someone is aging or how many years until they die. Even when used on the same person, the clocks can return different results. 

2. Epigenetic changes are dynamic.

Fluctuations in diet, environmental exposure, illness, time of day, and other factors could all influence epigenetic clocks. As a result, someone's estimated biological age could vary significantly depending on when they're tested.

3. It's difficult to create epigenetic clocks.

"[C]onstructing epigenetic clocks is technically challenging, and there is no established gold-standard method for generating clocks," Shalev and Apsley write.

For example, using saliva instead of blood samples to test epigenetic age can lead to significantly different results for the same person. The method to measure epigenetic marks is also evolving, which means that the original algorithms used may not always perform the same way.

"If insurance companies began using epigenetic age estimates to set premiums, many people could face higher costs for biological differences shaped by circumstances beyond their control, potentially deepening existing health disparities," Shalev and Apsley write.

What are the benefits of epigenetic clocks?

Although epigenetic clocks are generally not accurate at the individual level, they can help researchers study aging at the population level.

Several studies have used epigenetic clocks to identify lifestyle habits that could, on average, slow down aging. Some examples include reducing your daily calorie intake, exercising regularly, having a healthy diet, getting enough sleep, and not smoking. A recent study also suggested that taking a daily multivitamin could help slow certain signs of biological aging.

Epigenetic clocks can also be used to test new drug therapies designed to slow down specific aging processes. For example, researchers have found that rapamycin, a drug associated with different aging processes, can reduce the epigenetic age of human skin cells. Another study has shown that a treatment designed to regenerate the thymus could help slow or even reverse epigenetic aging after a year of treatment.

"Epigenetic clocks are helping scientists advance scientific research on the aging processes, but they aren’t medical tests to measure individual health," Shalev and Apsley write. "In the future, epigenetic measurements may play be useful in guiding personal health decisions. But for now, epigenetic clocks sold as biological age tests are best used and refined by researchers studying populations rather than individual people."