It is remarkable to me how some people are able to live to age 90 and beyond and remain totally independent and as sharp as a tack. Having long-lived parents is an important predictor of a long life, indicating that genes play a central role in longevity. But there are many other features characterizing the oldest of the old.

Almost always they are fit, exercise frequently and have a unique disposition and very high self-esteem. And yet, even if you seem robust and healthy, once you reach this age, resilience decreases substantially and a relatively minor incident can lead to a life-threatening illness. Something as simple as a viral infection can cause a rapid deterioration in health, often manifesting with confusion, reduction in blood pressure, incontinence, total loss of appetite and urgent admission to the hospital.

Unlike with a younger person, the ability to bounce back is slow and could take months before full recovery occurs. This often requires extensive rehabilitation that is often provided in transitional care units in nursing homes. Nevertheless, there is no question that even at age 90 and beyond, the return to complete independence is possible. This requires a great deal of persistence on the patient's part, a will to get well, excellent medical care and an aggressive physical therapy and nutrition program.

An increased susceptibility to illness and reduced ability to recover explains why influenza epidemics or weather disasters lead to a disproportionate number of deaths in older people. It is the elderly who die of heatstroke in the summer or cold exposure in the winter. During the recent floods in the United States, the vast majority of deaths occurred in older people who were less able to move rapidly to safety or who developed cardiac problems during the stress of the clean-up period. It is almost always those at the extremes of life (very young or very old) who are most vulnerable and who suffer the most during tragedies.

For those of us in our 60s, like myself, who are blessed with living parents, we all worry about the potential impact of illness. We become protective and do as much as we can to assure that our parents remain safe. We beg them to stop driving, to leave the large ancestral home; we ask them to move in with us, or consider an assisted-living facility. Our parents value their independence above all else and usually do not listen to our pleas.

Recently I had the privilege of meeting Jack Fleck, who in 1955 beat golfer Ben Hogan to win the U.S. Open. He typifies the very healthy older person determined to continue living in his own home with his wife, who, fortunately, is as healthy as he.

At age 86, he recognizes that he has lived a full life and is determined to accept risk rather than safety. I am sure that those who love him are concerned that he is taking on too much, but in discussions with him it is clear that he accepts that things could change any day but staying alive means that he must live life to the fullest.

However, we must understand that anyone who is very old has limited resilience, and we must be aware that a minor problem can be life threatening. Seeking medical help quickly is critical. It is important to understand that just because you are in your late 80s or 90s does not mean that an illness will invariably lead to a bad outcome. One of my key roles as a geriatrician is to assure that an older person is not discriminated against on the basis of age and that, in appropriate cases, there is often a significant ability to recover with rehabilitation.

We must always respect the wishes of our beloved parents and older friends. It is possible for them to remain independent and the risk is worth it. However, we must be aware of their increased susceptibilities and pay special attention to their needs should they become ill or exposed to a man-made or natural disaster.

Dr. David Lipschitz is the author of the book "Breaking the Rules of Aging." To find out more about Dr. David Lipschitz and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate Web page at www.creators.com. More information is available at www.drdavidhealth.com.

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