While it has become generally accepted that our lifestyles play a role in health and disease, most people believe that the ultimate determinant of longevity resides in their genes. Whenever I have asked a patient how long he or she expects to live, their first instinct is to say, ?Well, my mother died at age X, and my father?? This is another way of saying that my genes are my fate.



The twenty-first century has been heralded as the age of the genome, and medical genetics is widely touted as the future of health care. Diseases will soon be diagnosed by identifying the faulty gene; therapy will either fix or replace it. While genes are undeniably important factors in causing disease, their roles have been vastly overemphasized. For the most common diseases such as cancer and atherosclerosis, genes are predispositions, not inevitabilities.

Identical twins have the same genetic risk for disease, yet several studies have shown substantial differences in their health histories. This is because another crucial factor in determining one's propensity for disease: an individual's environment. According to Craig Venter, former CEO of the company that first decoded the human genome, ?The wonderful diversity of the human species is not hard-wired in our genetic code. Our environments are critical.?

A recent report in the New England Journal studied 44,788 twins to evaluate the comparative importance of genes and the environment in causing the most common types of cancer. The study concluded: ?Inherited genetic factors make a minor contribution to susceptibility in most types of cancer. The overwhelming contributor to the causation of cancer is the environment.? It is now widely accepted that 80 to 90 percent of human cancer is due to non-genetic factors.

The overriding importance of environmental elements is also clear in the development of atherosclerosis, the number one killer in the United States. Atherosclerosis is a multifactoral disorder resulting from an interaction of several predisposing abnormalities such as high cholesterol, hypertension and diabetes. Research has conclusively shown that reducing these risks substantially decreases the probability of having a heart attack or stroke. For example, a loss of just 7 percent of body weight in obese people reduces the incidence of diabetes by 58 percent, while shedding 10 pounds will normalize the blood pressure of those with borderline hypertension, no matter what their genetic propensity.

Genetic diseases generally fall into one of three categories. The first, called ?chromosomal disorders,? are caused either by excess or a deficient number of genes. Down's syndrome is an example of this type of disorder. The second, referred to as ?simple inherited disorders,? are primarily determined by a single abnormally altered or mutant gene. An example is sickle cell anemia, a disease affecting red blood cells.

The last and most common group is called ?multifactoral disorders? because they result from an interaction of multiple genetic and environmental factors. Coronary artery disease and most cancers fall into this category. Genetics experts agree that the risk of inheriting a disease is substantially lower in the multifactor group than it is in the first two groups.

Experience has convinced me that in addition to genes themselves, our minds? conclusions about our genes?something I call mental genetics?also has a major influence on our health and longevity. When we conclude that our parents? medical histories and their lifespans determine our own, that belief can create its own reality.

Some time ago, I met a man named Jerry who wanted to talk about his heart problem. He began by telling me not about himself, but about his father. Years before, Jerry was with family and friends in the woods near their cabin when suddenly a large snake appeared. Jerry's father ran up an incline to the cabin, ran back down with a rifle in his hands, shot the snake, and then fell to the ground. He was dead of a massive heart attack at age sixty-four. For jerry, who was thirty-seven at the time, heart disease became "my bugaboo." As he entered his sixties, he became filled with ominous thoughts and anxieties. His father's death felt "like a shadow pursuing me." It culminated in a heart condition when Jerry turned sixty-four. Fortunately, Jerry was lead to a physician whom he respected and whose advice he took. He began a program of exercise, stress reduction and a sensible diet, and has done well since.

People with a strong will to live understand that when they take life-enhancing measures, their health and longevity will be favorably affected regardless of their genes. They take responsibility for their lives instead of being at the mercy of circumstances. Remember: at times, our thoughts about our genes can have as much impact on our health and the genes themselves.