What is biological age?

The concept of biological age is typically attributed to Alex Comfort who wrote a paper in 1969 on the subject. But 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.

During our lives, our DNA accumulates molecular changes that turn different genes on and off, Smith reports. Horvath analyzed those changes in thousands of people and was able to create an algorithm to determine how those changes correlate with age.

According to Jesse Poganik, an instructor at Harvard Medical School who researches biological aging, these DNA changes happen naturally as we get older but can be accelerated by behaviors that affect health, like smoking and consuming excessive amounts of alcohol. As a result, biological age estimates have been found to correlate with life expectancy and health.

Why experts are wary of biological age tests

Many companies sell tests for around $300 that utilize Horvath's technology to determine your biological age. The tests analyze you blood or saliva and compare changes within your epigenome to population averages, Smith reports.

However, experts caution that these tests don't actually reveal much about your health, as they were originally designed to assess large groups of people rather than individuals, and because of this, their results can be unreliable.

It's also unclear what exactly an individual can do with the results of a biological age test, Smith reports. Scientists don't yet know how to reverse a person's biological age or if doing so is even possible.

There are also other tests on the market, including some that offer a panel of typical blood tests you'd receive at a doctor's office. These companies say many of the numbers on these tests, like cholesterol or hemoglobin A1C tests, increase as we age and can be used as a proxy for a person's biological age.

However, whether blood marker tests can track a person's biological age — rather than just their general health — is unclear, Smith reports. But one advantage these tests pose is the ability to measure things that can be changed. For example, if the tests show your blood sugar levels are too high, there are ways to lower them through medication and lifestyle changes.

"Expanding access and using more frequent testing to optimize health seems fairly reasonable to me," Poganik said. However, he added, "any claims of accurate, individual-level determination of biological age should be approached with caution." (Smith, New York Times, 12/19)

Centenarians, or those who are at least 100 years old, are a growing portion of the United States, and research says a mixture of good genetics and good habits are behind living to such an advanced age, Alex Janin reports for the Wall Street Journal.