The concept, physiologic reserves, was first described by Walter Cannon, a physiologist at Harvard Medical School in the first half of the 20th century. This refers to the ability of a human to summon the internal energy required to recover from an injury or an illness.
When our physiologic reserves start to diminish, we can become more susceptible to disease. As we age, our physiologic reserves go down. However, there is wide variation among individuals as to the extent physiologic reserves are preserved. Our genetic makeup and exposure to various environmental factors account for this variation.
Here are some of the examples of how our internal organs have reduced reserve. The size of the liver, and consequently the ability of the liver to filter out toxins declines about 30 percent over the age of 60. The size of our kidneys also diminishes and there is reduction in the filtration ability of the kidneys of about 30 percent by age 75.
There is also a tendency for hypertension to develop, as well as coronary artery disease, as we age. Lung function can also diminish with age. There is a reduction in exercise capacity for most people, as a result. The muscle mass in our limbs can be reduced by about 50 percent above the age of 70. In addition, the immune system becomes less effective as we age, which makes us more susceptible to infections as well as developing various kinds of cancer. Our brain shrinks after the age of 65 by small increments every year. Consequently, there is both reduced mental acuity and cognitive abilities.
Although this sounds somewhat pessimistic, there are many activities people can involve themselves in as they age in order to slow down the decline. Avoidance of cigarette smoke can prevent rapid decline in lung function; this would be true either for firsthand or secondhand cigarette smoke. Exercise training can improve blood pressure, heart function and lung function. Maintaining good hydration can help to preserve kidney function and more importantly, it is critical to avoid exposure to substances that can injure your kidneys.
The most common substances that causes kidney damage over time are non-steroidal anti-inflammatory medications, which people commonly take for pain relief due to arthritis and other painful musculoskeletal conditions. The importance of a healthy diet cannot be over emphasized. Since low-grade inflammation seems to be a part of normal aging, it is very helpful to follow a diet that helps to promote reduction in inflammation. An example of this would be the Mediterranean diet, which was talked about in an earlier column.
Preventing cognitive decline is also a high priority for all of us. Some of the preventative measures that we can take include correcting high blood pressure through healthy foods, salt restriction and if needed, medication. One should minimize exposure to medications that can slow down brain activity (sleep aides and sedatives). Again, following a Mediterranean-type diet can also be helpful.
A regular schedule of physical exercise also correlates with improving cognitive function. Being involved in stimulating mental activities such as learning a new language, or taking courses in higher education have also been shown to slow down cognitive decline. Interestingly, any involvement in musical activities has been shown to provide healthy stimulation of brain cells, which can reduce cognitive decline. So, learn to play a musical instrument, and make other healthy lifestyle changes to build up your reserves.
Dr. Mark Roth writes about internal medicine for the Cleveland Jewish News. He is an internal medicine physician with University Hospitals.