Physical activity/exercise is often viewed as a recreational activity to be engaged in by the young, or those who delight in the luxury of free time. This could not be more wrong! Physical inactivity is now the third leading cause of preventable deaths in the United States. My message is clear: Physical activity is medicinal and absolutely vital to good health.
This message is not new, as illustrated by a quote from Hippocrates 460 BC: "If we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health."
I have had the good fortune to watch my mother recover fully from critical illness. I saw two sides of coin: the great devastation that occurs from being bedridden and inactive (one-third of skeletal muscle in an immobilized limb can disappear in weeks) and the progress subsequently made by physical activity. This experience led me to investigate the evidence for a role of physical activity in medicine and health. Exploring new insights into the molecular mechanisms of exercise reveals just how it may exert its effects.
Exercise for cancer prevention and survival of cancer patients
Let's begin with cancer, my area of expertise. One of the most extensive evidence-based reports on exercise and cancer prevention, "The Food, Nutrition, Physical Activity, and Prevention of Cancer Report," states that there is convincing evidence that physical activity helps decrease the risk of colorectal cancer and probable evidence that it helps decrease the risk of post-menopausal breast and endometrium cancer. The World Cancer Research Fund and the American Institute for Cancer Research makes 10 recommendations for the prevention of cancer: one is be lean and another is to be active for at least 30 minutes every day. Note that although these two recommendations are related, they are different. Being a lean couch potato does not cut the mustard.
The report also states that maintaining a healthy body weight throughout life may be one of the most important ways to protect against cancer. Exercise is a means to this end. Another mechanism of exercise for reducing breast and endometrium cancer may be that it causes a decrease in circulating estrogen, a known risk factor.
More recently, exercise has been reported to be important for cancer survivors. Results from several studies shows that post-diagnosis physical activity reduces breast cancer deaths. The greatest benefit occurs in women who have hormone-sensitive tumors and who performed the equivalent of walking at an average pace for 3-5 hours per week. Recent evidence from breast cancer patients suggests that after six months of moderate-intensity exercise, DNA modifications (a decrease in methylation) occurred that increased the expression of genes and these events were associated with overall survival. One of the genes was a known tumor suppressor gene -- a gene whose product has a role in suppressing tumors.
Benefits for brain health
Many people are aware of prevention of cardiovascular disease by physical activity. Few people know about the studies that report that a high level of physical activity seems to delay the onset of dementia or that exercise helps to delay cognitive impairment. The function of the brain is dependent upon the transmission of chemical and electrical signals that are passed between nerve cells across a region called a synapse. Exercise can turn on genes that produce brain-specific growth factors that can modify the structure of the synapse and affect function.
Another indirect mechanism of exercise on brain health is that it reduces risk factors such as diabetes, cardiovascular disease, and hypertension, which can trigger neurodegeneration. One study suggests that the best effects to slow down cognitive decline can be found with moderate intensity exercise such as brisk walking for at least 30 minutes, five days a week.
Live longer and wear it well
The hard fact of aging is the body's decline of function: Muscles lose strength and mass, bones become fragile, the heart beats slower, and brain function becomes impaired before death. But new evidence shows that exercise is linked to mortality and aging. A recent 20 year follow-up study by Kokkinos and others showed that mortality risk in older men (age 65-92) is 38 percent lower for those who achieved exercise capacity of 5.1-6.0 metabolic equivalents (approximately an hour of brisk walking).
More exciting news is that a family of genes called sirtuins, identified as key longevity and quality of aging regulators, mediate the response to exercise and are involved in many processes that can alter the process of aging. In fact, if scientists experimentally add extra amounts of a specific sirtuin to male mice, it extends their life span by 15 percent. The products of the sirtuin genes work by regulating the expression of genes and modifying the activity of enzymes. This knowledge may even help provide a path to the "fountain of youth" by guiding the development of pharmaceuticals useful to prevent and treat symptoms of aging.
Moderate exercise is an antioxidant
Exercise creates highly-reactive intermediates of oxygen (reactive oxygen species (ROS), also known as free radicals). The role of free radicals in disease and aging is well documented. The theory that moderate exercise is an antioxidant fits within a theoretical framework that dose of exercise matters. High amounts of free radicals generated by intense exercise can damage cell components, including DNA, but low amounts from moderate exercise act as important signals that turn on powerful antioxidant genes (e.g., superoxide dismutase) and strengthen our defense against ROS. This antioxidant mechanism can explain many of the health benefits of moderate exercise.
My advice for a healthy life is to get out and be active: Get back on a bicycle, jump in the pool, battle the ocean waves, pick up a paddle, jog through the park, or pick up a racket. Think of it as investing in what I call a "health pension" -- investment in your health now for the years ahead. It could be the best thing you can do for your future. And take your friends and family. Enjoy staying healthy and live longer by being active. The power of exercise is that it can turn on YOUR genes-genes that help defend against disease and the aging process. Remember: Exercise is medicinal.
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