Healthy Aging and Senescent Cells

Extensive evidence shows that aging is associated with, and partially caused by, the accumulation of "senescent cells" in your body (Curr Opin Clin Nutr Metab Care, 2014;17:324–328). Recent animal studies have shown that it is possible to extend the lives of animals by reducing the numbers of senescent cells, even if treatment is started late in life (Nature Medicine, July 9, 2018).

What are Senescent Cells? As you age, the cells in your body also age and many cells become "senescent cells". Normal cells go through a certain number of doublings and then are programmed to die. This is called apoptosis and is normal for all healthy cells. For example, the cells in your lips live only up to 48 hours, skin cells live up to 28 days, and red blood cells up to 120 days. As cells age, their DNA can be damaged so that they do not die (Nestle Nutr Inst Workshop Ser, 2015; 83:11–18). Senescent cells are not normal because they:

• try to live forever instead of dying at their programmed time

• stop producing new cells, and

• lose their ability to perform their normal functions. For example, nerve cells lose their ability to transmit messages so you can become forgetful, uncoordinated, not able to move, or lose hearing or vision.

Most senescent cells are destroyed by your immune system in the same way it destroys bacteria and viruses. Your immunity recognizes bacteria and viruses that try to get into your cells by their surface proteins that are different from your normal cells. So your immunity makes white blood cells and chemicals called cytokines that attack and try to kill invading germs. In the same way, your immunity recognizes that senescent cells are different from normal cells and works to attack and kill them. Exactly the same cells and chemicals produced by your immunity to kill germs also are produced to attack and kill the senescent cells.

Senescent cells that are not destroyed by your immune system can become cancers (PLoS Biology, 2008; 6 (12): e301). Cancers do not become harmful as long as they stay in one place and do not overgrow a vital organ. For example, a woman does not die from breast cancer when it is limited to the breast. However, breast cancer cells can spread to the brain, bones, liver and other places to destroy these essential tissues and kill you.

How Do Senescent Cells Shorten Lives? As you age, senescent cells start to accumulate in your body. This increase in senescent cells causes your immunity to stay overactive all the time in an effort to rid your body of the senescent cells. An immunity that stays active all the time is called inflammation, and your overactive immunity attacks not only the senescent cells, but also normal cells in your body. This damages healthy cells, so more and more cells become damaged and senescent, which is the very definition of aging (Science, 2006; 311: 1257). An overactive immunity can punch holes in the inner linings of your arteries, causing plaques to form which can then break off to cause heart attacks. An overactive immunity can also attack and damage the DNA in your cells to form even more senescent cells, which can overwhelm your immune system and increase the chances that these damaged cells will become established cancers.

Inflammation of aging is a primary driver for age-related diseases such as Alzheimer's disease and atherosclerosis (Curr Pharm Des, 2010;16(6):584-96). People who live to be 100 appear to be able to live longer than other people because they suffer less damage from their overactive immunities called inflammation (Mech Ageing Dev, Jan 2007;128(1):83-91). Centenarians may be at reduced and delayed risk for cancer because they have reduced markers of inflammation such as IGF-1 and p53 (Cancer Immunol Immunother, Dec 2009;58(12):1909-17).

Fruits and Vegetables to the Rescue One effective way to reduce inflammation is to follow an anti-inflammatory diet. A diet that is loaded with fruits, vegetables and seeds and is low in added sugar, sodium and processed meats delays the markers of aging (American Journal of Epidemiology, October 1, 2018;187(10):2192–2201). As you grow older, the telomeres in cells shorten. Telomeres cover the tips of chromosomes in your cells and with each cell doubling, telomeres shorten, so doctors can measure aging by measuring the length of chromosomes in your cells. This study and others show that people who eat a high-plant, low-meat diet such as the DASH diet or Mediterranean diets have much longer telomeres than those who eat less healthful diets.

People who eat the most and widest variety of vegetables live the longest and have the lowest rates of heart attacks and heart disease (Nutrition Journal, July 10, 2018;17:67), most likely because fruits, vegetables and seeds are full of polyphenols and fiber. Polyphenols in fruits and vegetables reduced the number of senescent cells in mice to reduce disease and extend their lives (EBioMedicine, September 29, 2018). Furthermore, fruits, vegetables and seeds (beans, whole grains, nuts and so forth) have lots of soluble fiber, and bacteria in your colon ferment soluble fiber into short chain fatty acids that reduce inflammation and lower high blood pressure and cholesterol.

My Recommendations A major component of aging is the accumulation of senescent cells that stop performing their jobs that are necessary to keep you healthy. These cells then turn on your immunity to cause inflammation that can attack and destroy even more cells throughout your body. You can help to delay aging, prevent disease and live longer by following an anti-inflammatory lifestyle of:

• eating lots of fruits, vegetables, nuts, beans, whole grains and other seeds

• restricting red meat and processed meats, sugar-added foods, fried foods, and all drinks with sugar in them including fruit juices

• exercising

• avoiding overweight, particularly excess fat in your belly

• avoiding anything that damages cells such a smoking, drinking alcohol or exposure to other harmful chemicals

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