(Editors note: This article is part of an editorial partnership between Next Avenue and The American Federation for Aging Research (AFAR), a national nonprofit whose mission is to support and advance healthy aging through biomedical research.)

Are you as old as you feel, as old as you look or as old as your birth certificate says? The best answer may be none of the above.

Actually, you may be as biologically old as your blood says you are.

For many years, aging researchers have sought markers of biological age, or biomarkers simple signals that reveal the expected length of your future health. The expected length of future health, after all, is the key biological difference between younger and older people.

Some people have called such markers biological clocks. I dont know about you, but I dont typically calculate my age by thinking of clocks. I think of calendars. So, I prefer to call these hypothetical signals biological calendars.

The importance of these calendars is that they potentially allow researchers to quickly see whether a new drug, diet or other treatment that purports to slow, or even possibly reverse, aging is actually doing so.

Biological calendars of aging can also provide rapid feedback on how a lifestyle change, such as in diet or exercise habits, is affecting your biological age. This insight can motivate people to stick with that change.

Now, as a biological calendar, blood is a devilishly complex stew. Like a stew, it is liquid with lumps in it. We call the liquid plasma; the lumps, cells. Physicians for the past century have been using chemical analysis of plasma and counts of the various blood cell types to diagnose diseases. But we are now entering a brave new world of blood analysis.

Plasma contains not just the dozen or two chemicals that standard laboratory tests measure; it contains a constantly changing mixture of vitamins, nutrients, waste products, hormones and thousands of different proteins.

A hint that plasma might hold secrets about aging has come from research in which the plasma from young mice (or humans!) was found to rejuvenate the function of muscles, brain, heart and other organs of old mice. Dracula, it turns out, may have been onto something.

Recent advances in chemical analysis allow us to measure thousands of plasma chemicals at once, and advances in machine learning are helping make sense of that torrent of information. Plasma proteins may turn out to be just the type of biological calendar we are seeking.

I say this because a recent study of about 3,000 plasma proteins found that a specific combination of 373 of these proteins could accurately tell the age of the person from whom it was drawn. The study was conducted by AFAR Scientific Director Dr. Nir Barzilai with AFAR grantees David Gate of Stanford University and Dr. Sofiya Milman and Dr. Joe Verghese, both from the Albert Einstein College of Medicine in New York.

On top of that, people who were judged by their proteins to be younger than their real age scored better on a panel of physical and mental tests. We dont know yet how well these proteins might predict future health or life, but those studies will soon follow.

Blood cells, in addition to plasma, might have an even more promising aging tale to tell.

Your white blood cells (but not your red cells) contain your DNA, which provides the instruction manual for pretty much everything that goes on in your body. A few years ago, it was hoped that telomeres those protective DNA caps at the ends of your chromosomes from white blood cells might be a useful biological calendar. But telomeres as predictors of future health have not held up to scientific scrutiny.

However, we may have just been looking at the wrong part of our DNA.

Although we tend to think of DNA as little more than a long-coded sequence of DNA letters, there is a bit more to it. In particular, there are a number of small chemical tags that attach to DNA at specific sites to help turn off, or turn on, genes.

In recent years, combinations of particular tags called DNA methylation have, like plasma proteins, been shown to be good predictors of age and health in people and animals. These tags have even been shown to predict time to death and the development of later life diseases in people.

Perhaps even more exciting, a small, very preliminary study of 10 middle-aged men taking a hormone cocktail designed to stimulate the immune system showed a one-and-a-half-year regression in their DNA methylation calendar.

Lets not get too excited about this result yet. It is easy to overinterpret such very preliminary results, as some of the media have done. We have no idea at present what a small backward trend in DNA methylation age means, and this study has more than a few limitations. But it is without doubt provocative.

Stay tuned. Analysis of blood cells and blood plasma may hold secrets of aging that we are just beginning to discover.

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Does our blood hold the secrets of our longevity? - The Oakland Press