Just as you must wrap the ends of a strand of dental floss around your fingers in order to clean between your teeth, chromosomes of eukaryotes (the kind of life that includes humans) must have slack on their DNA strands. Known as telomeres, these tips of the DNA strands are shortened during each replication cycle, or mitosis, of body cells. Normally, chromosomal telomeres are fairly long at the beginning of life, meaning in early generations of body cells. Because they do not contain any genes, telomeres keep cells healthy by protecting genes located closest to the extremes of the chromosome from being snipped away when the chromosome reproduces. This preserves the genes for future generations of cells and prevents chromosomes from sticking together.
Telomere length is a topic that comes up often in genetics research. Over the years, studies have connected telomere shortening with aging, a variety of degenerative medical conditions, and cancer. Telomeres are shortened not only based on the number of times a cell line goes through mitosis, but also due to environmental stresses, such as radiation exposure, and spaceflight. Last June, researchers at Tulane University discovered another stress that can shorten telomeres: physical domestic abuse. Because they are accessed easily by taking blood samples, telomere studies typically are conducted on white blood cells (leukocytes). However, telomere changes in blood cells are thought to reflect changes in telomeres in other cell types too.
Stress is not the only factor that affects telomere length, though. Looking at white blood cells of nurses participating in a large study that has been going on for decades, an analysis published earlier this month found that strict adherence to the Mediterranean diet keeps telomeres long. Basically, the Mediterranean diet emphasizes whole grains, vegetables, fruits, nuts, and olive oil, keeping saturated fat, trans fat, and sugar intake at a minimum while maximizing the intake of monounsaturated fats, omega-3 polyunsaturated fats, and complex carbohydrates. For some time, the diet has been known to reduce the risk of diabetes, heart disease, and strokes, partly by keeping sugar and “bad cholesterol” at low levels while keeping the level of “good cholesterol” high. But the direct effects of blood cholesterol and sugar are not enough to explain why the diet has as much of an effect on overall health as it does. Not only does it reduce the risk of heart disease, strokes, and diabetes; the diet also slows cell aging and reduces the risk of cancer. Now, the newly demonstrated connection with the length of telomeres explains how this anti-aging effect happens.
Because it promotes overall health by reducing the risk of the very common and dangerous conditions like heart disease and strokes, the Mediterranean diet is probably going to turn out to be good for most people. Nevertheless, we have to be cautious when expanding preventive therapies beyond diet to more aggressive approaches. In particular, we need to be careful about developing medications specifically to lengthen telomeres throughout the body. For example, drug developers are currently able to target an enzyme called telomerase. Normally, cells use telomerase to cut down the telomeres, but, by interfering with the enzyme’s function, experimental drugs can keep telomeres long.
Like most things in life, too much of a good medicine, or even a good food, can end up doing damage. Changing our analogy from dental floss to shoe laces, you need slack on the laces to tie your shoes. Too much slack, however, will cause you’ to trip. One question that scientists have not been able to answer, yet, is: Is it possible for telomeres to be too long – so long that they actually could do harm?
Unfortunately, the answer appears to be yes, at least for certain types of cells. A recent study based at University of California/San Francisco and the Mayo Clinic discovered that having certain genes that cause telomeres to be longer than normal increases a person’s risk of developing gliomas – malignant brain tumors. One possible reason is this: When cells age, short telomeres make the cells vulnerable to being killed off by body systems. When the body kills off a cancer cell, it prevents the cancer cell from developing into a malignant tumor. But if that cancer cell has long telomeres, the likelihood that it can continue to live and replicate is increased, leading to the development of a tumor.
Since gliomas are very rare, while conditions like heart disease, diabetes, and strokes are very common, nobody is saying that you should avoid a diet that keeps your telomeres long. From a benefit/risk perspective, stocking up on olive oil, nuts, and fish certainly looks like a good idea. But, like other discoveries in nutrition and medicine that seem to show the opposite of what is generally thought to be true, the glioma study is a warning that there’s more to telomeres than meets the eye.
Written by David Warmflash
David is an astrobiologist and science writer. He received his M.D. from Tel Aviv University Sackler School of Medicine, and has done post doctoral work at Brandeis University, the University of Pennsylvania, and the Johnson Space Center, where he was part of the NASA's first cohort of astrobiology training fellows. He has been involved in science outreach for more than a decade and since 2002 has collaborated with The Planetary Society on studying the effects of the space environment on small organisms.