The Many Ages of You

Cell turnover means that much of your body is younger than you think. Use this science to promote healthy aging.

How Old Are Your Cells?While you have one official birth date, your body is in a state of perpetual rebirth. Each second, millions of cells naturally die off and are replaced by brand-spanking-new ones. "The average age of a cell in an adult’s body is only about seven to 10 years," says Jonas Frisen, MD, PhD, a stem cell biologist at the Karolinska Institute, in Stockholm. His team can back this up, thanks to a technique they’ve developed that pinpoints the age of specific cells in tissues and organs.Frisen hopes his work will eventually provide the key to treating diseases and perhaps even slowing the aging process. "Some diseases, like anemia, are caused by the body’s reduced ability to generate new cells," he says. Others, such as cancer, are caused by the production of too many cells. "Knowing the normal turnover rate of different cells in health and disease can help us understand if it is rational — and realistic — to modulate the process of renewal or perhaps replace cells that have been lost," Frisen notes.For now, having a general chronometer for individual cells may help you stay healthy longer. "Despite cell renewal, the DNA mutates from one cell generation to the next, so cells become less efficient at renewing themselves," Frisen explains. That’s where behavior and environment come in: "Smoking, the sun, and chemical exposure accelerate DNA mutation." Use the following body age map to help yourself look and feel as young as you can.Your Brain and EyesYour Cerebral CortexNeurons in your cerebral cortex — the seat of your senses, conscious thought, and behavior — are exactly the same age as you are. In other words, your body doesn’t make any new ones. When brain cells die here — from excessive alcohol consumption, drug use, or disease — you generally lose them for good.Your CerebellumCells in your cerebellum, the area of the brain that controls physical movement, are about 2.9 years younger than you are, probably because your cerebellum and motor coordination skills aren’t fully developed until you are a few years old.Your HippocampusIn the cells of the hippocampus, Frisen has found clear evidence of cell turnover, which plays a key role in how we form memories. The lack of adequate cell production in this part of the brain is closely associated with Alzheimer’s as well as depression.Your EyesThe inner core of your lens is even older than you are, since it finishes developing while you are still in utero. But cell growth in the lens area doesn’t stop altogether, says Bruce Buchholz, PhD, a scientist at the Center for Accelerator Mass Spectrometry at the Lawrence Livermore National Laboratory, in California. "New cells continue to form in onionlike layers, and few of them die off," he says. "Part of the reason you have a harder time focusing as you get older is because the lens gets bigger and has a harder time changing shape so it can focus." Over time, accumulated damage to the lens cells contributes to the formation of cataracts. Wearing UV-protective sunglasses to slow the process is your best bet.Your Blood, Skin, and HeartYour Red Blood Cells These oxygen-delivering cells last only about 120 days before they are disposed of via the spleen. "Blood cells are hurtled around the body at breakneck speed through very narrow passages," explains Ralph Green, MD, PhD, chair of the department of pathology and laboratory medicine at the University of California, Davis. The key to cell health, Green says, is to nourish the marrow, where red blood cells are produced, which means "taking in adequate levels of vitamin B12." It’s difficult to get enough B12 from your diet, so a daily supplement of 10 micrograms is a good idea.Your White Blood Cells There are many types of white cells with widely varying life spans. Some jet off to fight infection and die within a day; others stoke up antibodies and can last for years. As you age, Frisen says, you become less efficient at producing these cells. Keeping your body free of infection, and of physical and mental stress, can prevent your immune system from being overtaxed.Your Skin The cells you’re wrapped in last a brief 14 days, and there’s a nice fresh batch of skin waiting to surface. So why do you wrinkle regardless of this renewal? All arrows point to the gradual mutation of your DNA, which degrades the quality of your structure-providing collagen and paves the way for signs of aging. Daily use of sunscreen can help reverse some of this damage.Your Heart It has long been suspected that cardiac cells do not renew themselves. That may be why heart attacks cause permanent damage and you lose cardiac function as you age. In his latest research, however, Frisen says he has detected new-cell growth in the heart, which may lead to new ways to restore function after a heart attack.Your Muscle, Gut, Liver, and BonesYour Rib Muscle Cells here are about 15.1 years old. Your Gut Much like the skin, the lining of your stomach and intestines endures a lot of wear and tear, lasting but five days. Frisen found that cells in the body of the bowel, below the surface, are about 15.9 years old.Your Liver The cells in this filtering organ turn over every 300 to 500 days. Even so, to keep yours in peak form, avoid taking unnecessary medications, limit alcohol intake, and minimize deep-fried and fatty foods, which may contribute to the risk of gallbladder disorders, such as gallstones. Also use insecticides, spray paints, even aerosol cleaners sparingly since they are absorbed directly into the skin and lungs, taxing the liver and, in some cases, killing off cells.Your Skeleton Each year about 10 percent of your bone tissue is actually replaced, meaning your entire skeleton turns over every 10 years. Once you reach peak density, in your 30s, you begin to lose more bone than you build. The rate of bone loss increases after menopause. Weightbearing exercise (hiking, walking, running), strength training, and taking in plenty of calcium and vitamin D may stave off some loss.Originally published in MORE magazine, May 2007.

First Published Mon, 2009-04-06 18:02

Find this story at: