The Free-Radical Theory of Aging: Part I: How it all began; An interview with Dr. Denham Harman


by Richard A. Passwater, Ph.D.

During the past few months, I have been sitting the stage for this interview with Dr. Denham Harman, the originator of the free radical theory of aging. The concept that free radicals were involved with the deterioration of human biochemistry was the biggest advance since the discovery of germs. The discovery that free radicals are at work to impair the human body goes beyond the aging process to include the killer and crippling diseases once thought to be the result of aging. Free radicals are now known to be involved with cancer, heart disease, arthritis and perhaps as many as eighty diseases not caused by "germs." It all started with Dr. Denham Harman. I have known Dr. Harman since 1967 and he has freely shared his research and thoughts with me through the years. I will try to tell you the story behind Dr. Harman's discovery of how free radicals affect our bodies as well as report on some of his major findings.

Even though I have been very familiar with Dr. Harman's research findings, there were a few questions that I had never thought to ask him before, because during the 1960s and 1970s, the research findings were so exciting, we were to too busy looking ahead to take the time to think back. After forty years, it's time to pause and reflect. I started this interview in 1992, but I wanted to provide you with the background information necessary to understand the free-radical theory of aging before publishing the interview. Drs. William Pryor and Lester Packer were kind enough to set the stage with their explanations of free radicals and antioxidants. On October 14-18, 1994, the joint meeting of the American Aging Association and the American College of Clinical Gerontology dedicated the joint meeting "Towards the Golden Age of the Free Radical Theory of Aging," paying honor to Dr. Harman and to forty years of the free radical theory of aging. On that occasion I again met with Dr. Harman to finalize this two-part interview.

Dr. Harman is a true genius. Unfortunately, much of his research was too early to be appreciated. He was too far ahead of his time. In preparation for the interviews, I dug out my collection of Dr. Harman's research reports for review. I had forgotten several of his experiments that had to be put aside at the time, because there was so much to do with the free-radical theory of aging itself. Dr. Harman had always amazed me, but I was flabbergasted to see that I had forgotten his research on heart disease and cancer, that was ignored then, but today is the subject of current interest by several researchers who think they are having original thoughts. Unfortunately, most computer data bases don't go back before 1967 and thus much of Dr. Harman's research is buried in the pre-1967 literature stored in boxes in library basements..

Passwater: When you conceived the free radical theory of aging, virtually no one else was looking at the role of free radicals in biological systems. let alone in the aging process. When exactly did you conceive this concept?

Harman: In the first part of November 1954.

Passwater: It's apparent from your use of free radical scavengers that were effective radiation protectors that your background includes an extensive knowledge of radiation chemistry.

Harman: Yes, radiation chemistry was included in a number of my chemistry and physics courses in college. In addition, my work with free radical reactions while at Shell Development Company exposed me to studies of radiation chemistry.

Passwater: Why did you become interested in the aging process?

Harman: I guess I was always curious about it, but my interest in aging was sparked in December 1945 by an article in a popular magazine that my wife had called to my attention. The article, "Tomorrow you may be younger," was written by William Laurence, science editor of the New York Times. It was concerned with the research of Dr. Alexander Bogomolets of the Institute of Gerontology in Kiev, Russia, on an "antireticular-cytoxic serum."

On July 1, 1954 I joined the Donner Laboratory of Medical Physics on the Berkeley Campus of the University of California as a research associate of Dr. John Lawrence, the Director of Donner and the brother of Nobel Laureate Ernest Lawrence, the inventor of the cyclotron. I spent four years at Donner: the first two years I was full time, part time during the second two years while I completed my residency requirements in internal medicine in San Francisco. My time was my own except for Wednesday mornings in the Hematology Clinic. I took advantage of this free time to pursue my long-time interest in the cause of aging. Because aging is universal, I felt that aging might have a single basic cause.

In retrospect, I was probably uniquely qualified to approach the aging problem. I had the time, I had the interest, I had just completed a superb course in biology -- medical school at Stanford and a rotating internship on the Stanford Service at the San Francisco City and County Hospital, and I had over 15 years of almost continuous work in the chemistry laboratories of Shell Oil Company. I was fortunate to work for Shell. During my time there I obtained my B.S. and Ph.D. degrees from the College of Chemistry at the University of California in Berkeley: my graduate work was concerned with mechanisms of organic reactions. During my last seven years at Shell, I worked in the Reactions Kinetics Department, where I was involved almost entirely with free-radical chemistry, primarily with molecular oxygen and compounds of phosphorus and sulfur. This was in the early 1940s.

The first four months at Donner was a period of progressively increasing frustration. Every possible lead I thought of led nowhere. The frustration ended suddenly one morning during the first part of November, 1954. While reading in my office, it suddenly occurred to me that free radical reactions, however initiated, could be responsible for the progressive deterioration of biological systems with time because of their inherent ability to produce random change. I realized that free radicals could account for all the phenomena that I knew about because they were irreversible reactions. At that time there was no datum to indicate they were going on in the human body, but it was quite obvious that they had to go on because it was just the nature of chemistry. Our cells are exposed to oxygen all the time and I reasoned that there was a strong probability that free radical reactions were occurring. This would tie together all the material I knew -- the biology and the chemistry made sense when I looked at it from that point of view.

One day during the first part of December, 1954 I walked around the Berkeley campus and spoke with a number of people about the theory. The general reaction was negative, the theory was too simple to explain such a complex process as aging. I tried to point out, without much success, that free radical reactions could be very complicated. Only two of those I chatted with felt that the theory might have merit; they were both chemists with biological interests -- one in virology and the other in photosynthesis.

The theory was first published on July 14, 1955 as a University of California Radiation Laboratory report titled "Aging: a theory based on free radical and radiation chemistry" and as a journal article a year later in the Journal of Gerontology. The first talk, "Aging: the theory based on free radical and radiation chemistry with application to cancer and atherosclerosis," was presented on February 6, 1956 as a Donner Laboratory Seminar.

Passwater: Approximately how old were you when you had this out of the blue experience in November of 1954?

Harman: I was 38 at that time.

Passwater: Today, you are still at the University of Nebraska, a quick calculation suggests that you reached retirement age about 13 years ago. Yet, I sense that you are not doing just "professor emeritus" things, but are very active.

Harman: Although I am officially retired the University has been very good to me by providing an office where I can continue to work.

Passwater: Thank goodness for all the years you did that.

Harman: It's been interesting.

Passwater: I know that it is rewarding to keep track of all of the diseases that are now linked to free radicals. The list (see Table 1) reads like the table of contents of a general medical text.] A study by Pracon, Inc., of Reston Va., concluded that if Americans took optimal amounts of three antioxidant nutrients -- beta carotene, vitamin C and vitamin E -- we would save $ 8.7 billion annually from reduced hospitalizations for heart disease and cancer alone.

Harman: Free-radical reactions are implicated in 50 disorders. These "free radical diseases" include cancer, heart attacks, strokes, rheumatoid arthritis, cataracts, and Alzheimer's disease -- the major cause of admission to nursing homes. The list keeps growing.

Passwater: I would not be surprised if the list eventually exceeds 80 diseases. Before your free radical theory, it was just germs and aging -- and aging was some unknown thing. Now we have disease pathology that we can follow. I'm still thinking about how you were reading when the theory fell into place in your mind. Please tell us more about that experience.

Harman: It's a common experience to work for a day on a problem, say in chemistry or physics, and to finally give up and go to bed. Then after going to bed and not even trying to think about the problem, and just before dropping off to sleep, the answer comes to you -- it just pops into your head. When it happens, you know it is correct. All the pieces fall together. This was essentially what happened with the aging problem except that it took over four months of intense and frustrating effort to arrive at the solution.

Passwater: Journals aren't always interested in publishing new ideas -- they usually want new data. Here you have a brand new idea and it does get published. It wasn't until 1961 that I found your 1956 article, "Aging: A theory based on free radical and radiation chemistry," which was published in the Journal of Gerontology." That paper was largely theoretical, but it caused me to look beyond the "cross-linking" agents that I was working with and to look at the broader role of free radicals. You were able to get this "radical" idea published in the Journal of Gerontology.

Harman: I believe I sent it to a couple of other journals first, but they turned it down.

Passwater: Did they give a reason? Did they think that it just couldn't be or what?

Harman: It is hard to say. Journals like to publish something "concrete" so to speak. Today we have a journal for theoretical concepts called "Medical Hypothesis." At that point there was no such journal.

It didn't take me long to realize that if the theory was to be accepted, it would have to be reduced to practice. Based on the theory, studies were started in four areas: catalase, cancer, atherosclerosis, and life span extension.

Catalase is an enzyme that breaks down hydrogen peroxide to oxygen and water. By analogy with the Fenton reaction, which degrades hydrogen peroxide by a free-radical pathway to also give oxygen and water, we hoped that a study of catalase would provide evidence for the formation of the hydroxyl free radical in vivo. The data we accumulated were suggestive but not conclusive. Around the time I started to work at Donner, studies were in progress in St. Louis with the first electron spin resonance spectrometer (ESR). Free radicals were demonstrated to be in yeast; this was the first direct evidence that radicals were present in a biological system.

Passwater: When did you start your laboratory animal studies using radiation protectors and/or reducing agents, and when did you include vitamin E in your animal studies?

Harman: For ascorbic acid (vitamin C), around the same time as the catalase studies; a life span study with vitamin E using mice was conducted in 1968 -- it increased the life span by about 5 percent.

Passwater: Today, free radicals, antioxidants, and your work, are almost household words or buzz words among lay persons who are well-read in popular nutrition. Yet, in the 1960s, hardly any scientists were following your research. You were able to continue publishing and attract enough attention from enough scientists to bring your ideas to the forefront. How did you go about the necessary task of getting other people interested?. If you hadn't, your research and free radical pathology might still be buried for another twenty years yet.

Harman: Our first longevity study showed that the addition of a simple sulfur-containing organic compound to the diet of mice significantly increased the life span; it was published in the Journal of Gerontology in 1957. This called attention to my research, even if they didn't understand or believe the theory behind it. In 1962, I reached a larger group of scientists by publishing an article in Radiation Research based on the promising data we had accumulated. Research proceeded slowly during the first ten years of the theory. However, by the mid-1960's enough data had been accumulated to make it obvious that the average life span at birth, but not the maximum life span, could be increased by decreasing endogenous free-radical reactions with antioxidant supplementation or diet modulation. The failure to increase the maximum life span led to the publication in 1972 of a short paper in the Journal of the American Geriatrics Society that modified the free-radical theory of aging by suggesting that the life span was determined by the rate of free radical damage to the mitochondria.

Passwater: Please tell us more about your initial lifespan studies with vitamin C.

Harman: Vitamin C was included in our first life span experiment mentioned earlier. At two percent by weight in the diet, it had no effect on the life span of mice -- probably because mice mice produce fairly large amounts of vitamin C in their bodies.

Passwater: Let's go back to the compounds you chose for your first practical experiments. They were sulfur-containing radiation protectors. I think that your early work and that done at the AEC gave me a fondness for sulfur-antioxidants.

Harman: I was somewhat familiar with radiation chemistry at that point and I knew that one of the most effective compounds that the Atomic Energy Commission came up with was 2-mercaptoethylamine (2-MEA). I thought that it should increase life expectancy and it did. In mice, the addition of 0.5 percent by weight of 2-MEA to the diet will increase the average life expectancy at birth by about 20 percent. In man this would be equivalent to increasing the average life span from around 75 years to about 90 years.

Passwater: That is about what the average human life span should be -- around 85 to 90 years, and the maximum life span should be about 115 years. Why did you choose 0.5 percent of the diet for your test antioxidant?

Harman: Well, we used two concentrations. We didn't know where to start. There was no data to go on. It was obvious if you used too much you would kill the animals and if you used too little you wouldn't see anything. We were very lucky. We happened to select a concentration that showed some effect. That's just luck. We had no way of predicting that.

Passwater: Today, there is interesting research with phenylbutylnitrone (PBN). Research on shock trauma by Dr. G. P. Novelli of the University of Florence in the mid-1980s showed that PBN reduced free-radical damage., and more recently, Dr. John Carney of the University of Kentucky and Dr. Robert Floyd of the University of Oklahoma have found that PBN is very effective in blocking strokes in aged gerbils induced by free radicals.

Harman: Yes, Dr. Carney's group's finding published in 1991 is extremely interesting and important. It described the effects produced by administering PBN to gerbils in which, over a two-week period, the PBN returned the parameters studies, including a test of memory, back to those of young gerbils. The PBN was then stopped, and the parameters studied returned to their pre-test conditions.

Passwater: Dr. Richard Cutler of the National Institute on Aging's Gerontology Research Center in Baltimore has done some promising research with PBN too. He once described PBN as the most effective biological free-radical scavenger he has ever seen. His preliminary experiments are suggesting that PBN is effective even when given to aged mice. Dr. Cutler's group also presented two interesting posters on PBN's effect on mouse life span and the biochemical mechanisms involved with PBN at the First International Conference on Oxidative Stress and Aging held in Kona in March 1994. Have you ever tested PBN?

Harman: I have never evaluated PBN. Because of the 1991 paper I just mentioned, I suspect that many scientists are now doing so.

Passwater: When your free radical theory of aging was brand new, how did you get funding to prove your hypothesis. Laboratory animals studies aren't cheap. You had to convince somebody that your research warranted funds.

Harman: Laboratory animal studies are very expensive. Fortunately, I was at Donner Laboratories and they had the facilities and funds to support this research. So I didn't have to seek outside support for the initial studies. However, subsequently this has been a problem.

Passwater: Yes, especially when those who control the funds are sitting on their pet projects and want to fund their pet projects and don't want to hear new ideas that might show that their pet ideas are wrong. They got to head the funding process in the first place because their pet ideas seemed to be so important, and this gives them motivation to keep trying to prove their ideas correct, even when the evidence forthcoming is not supportive..

Harman: Actually I was fortunate I was able to demonstrate that the life span could be extended by antioxidants, so when I did apply to the National Institutes of Health for a grant, I had some data to support the application.

Passwater: Yes, it seems that when we get a new idea, we have to "boot-leg" the first study and use that result to show that the concept could possibly work. Then, it becomes a matter of keeping one study ahead of the funding requests

How do antioxidant nutrients contribute to health and longevity?

Harman: Free-radical reactions can cause deleterious changes throughout the body. Antioxidants decrease this damage and hence contribute to health and longevity.

In talking about longevity, a distinction should be made between average life expectancy at birth and the maximum life span. The former we can do something about -- it has increased from around 47 years in the United States in 1900 to about 75 years today. The maximum life span of man -- the longest any individual has lived -- remains unchanged at 115 - 120 years. Most of the antioxidants being used today increase average life expectancy but have little, if any, effect on maximum life expectancy. This observation in the mid-1960's prompted the suggestion that I mentioned earlier that the rate of aging of the mitochondria determined the maximum life span; a great deal of research is now going on in the field of mitochondrial aging.

Passwater: It seems so obvious today, but it wasn't until your paper appeared in the Journal of the American Geriatrics Society that the suggestion was made that the mitochondrion might serve as the biologic clock. The inner membrane permeability of the mitochondrion is highly selective as to what can pass through it, yet the mitochondrion is where most of the oxygen reactions occur. Thus, most of the free-radical damage may occur in the mitochondria, where it is not subject to modification from the outside because of the difficulties in getting antioxidants into the mitochondria in sufficient quantity or concentrations to do anything. It was a very fortunate deduction because today a great deal of work is going on in the field of mitochondria and aging.

The mitochondria are the "energy factories" in our cells that convert our food components into by-products and energy. In the digestive process, food is broken-down into smaller components which are then absorbed and transported by the blood to nourish the cells. Still, the digested food components are complex organic molecules. The mitochondria in our cells can further degrade these complex molecules into simpler products, ultimately producing the waste products carbon dioxide and water. In this process, mitochondria produce adenosine triphosphate (ATP), which becomes a source of energy for the body. ATP is much like a charged battery, and adenosine diphosphate (ADP) is analogous to a discharged battery. The free energy is stored in the phosphate bonds of these high-energy phosphates. When the body needs energy to drive a biochemical reaction, it usually involves ATP going to ADP somewhere in the process. The mitochondria recharge ADP back into ATP.

When we eat a lot or exercise, we increase the energy reactions in the mitochondria and the oxygen that is needed in those reactions. How much we eat helps determine how much oxygen is consumed in the mitochondria. Thus, the more we eat, the more we increase our need for antioxidant protection. Let's discuss what happens when we reduce these reactions? Hasn't it been shown that maximum lifespan can be increased by decreasing free radical production by the mitochondria by decreasing food intake?

Harman: Decreasing caloric consumption can indeed increase maximum life span. Decreasing the caloric intake of rats decreased body weight and oxygen consumption by 40 percent, increased average life expectancy at birth by 40 percent, and increased maximum life span by 49 percent. I believe these effects are caused by the lowered oxygen utilization; one to three percent of the oxygen we use is diverted to the superoxide radical and hydrogen peroxide. In essence, by decreasing caloric intake we decrease our exposure to internal radiation.

Passwater: You said that most antioxidants used today increase average life expectancy, but not maximum life span. What antioxidants do increase maximum life span?

Harman: Three antioxidants have now been reported to increase the maximum life span. One is the simple compound 2-mercaptoethanol; this is very similar to 2-MEA except that there is a hydroxyl (OH) group in place of the amine (NH2) group. Unfortunately it has an unpleasant odor.

Passwater: That means it works! If people would understand the value of the sulfur and selenium compounds, they would appreciate the odor. I keep running into people who don't take N-acetylcysteine (NAC) or sulfur-containing amino acids because they have strong odors. Even the health food pioneers appreciated the value of these odorous sulfur compounds. Sorry, I didn't mean to interrupt.

Harman: Dr. Emanuel and his associates in Moscow claimed that two pyridine compounds increased both the average and maximum life spans of mice by about 20 percent. I would like to see this study, as well as the one with 2-mercaptoethanol verified -- there are many variables in animal studies.

The search for compounds that can slow down the rate of production of free radicals by mitochondria without depressing ATP formation is an important and interesting field of research. Today we know a great deal about the effects of age on mitochondria. Research in this area should mushroom in the next few years. Hopefully it will lead to measures that decrease free radical reaction initiation by the mitochondria without significantly decreasing ATP production.

Studies of "mitochondrial diseases" indicate that the degeneration of mitochondria can be slowed in some cases. Apparently, the most effective nutrient in coenzyme Q-10.

Passwater: Coenzyme Q-10 is available as a dietary supplement.

Harman: Right. Many people take 10 - 30 milligrams three times a day. Coenzyme Q-10 is a normal component of the respiratory chain. The respiratory chain is the series of catalysts in the mitochondria that control the desired oxygen reactions. The concentration of coenzyme Q-10 in the respiratory chain decreases with age -- the cause is not known. Coenzyme Q-10 is being used to successfully treat myocardial myopathy. Coenzyme Q-10 is more than an antioxidant; it also slows the rate of mitochondria degradation without interfering with the rate of ATP production.

Passwater: How do you define the aging process today?

Harman: Aging is an accumulation of diverse adverse -- aging changes -- in the cells and tissues that increase the risk of death. These are responsible for both the commonly recognized sequential alterations that accompany advancing age beyond the early period of life, e.g., decrease in vision, graying of the hair, etc., and the progressive increases in the chance of disease and death associated with them. Aging changes can be attributed to development, genetic defects, the environment, disease, and to an inborn process called "the aging process."

The chance of death of an individual of a given age in a population -- readily available from vital statistics data -- serves as a measure of the average number of aging changes accumulated by persons of that age, i.e. of physiologic age, and the rate of change of the chance of death with time as the average rate of aging.

Today in the developed countries, premature deaths have reduced to a near minimum value so that the aging process is the major risk factor for disease and death after about age 28. Only one to two percent of individuals born today will be dead by age 28, the remaining 98 to 99 percent will die off at the exponential rate determine by the inborn aging process, so that most will be dead by age 100 and none will live beyond 115 to 120 years. These data are presented in a paper published in June 1991 in the Proceeding of the National Academy of Sciences entitled, "The aging process: major risk factor for disease and death."

Passwater: Yes, you make the point that we should concentrate a lot of effort in slowing the basic aging process because we have pretty much reduced the contributions of disease and environment, -- we still have them of course but we have reduced them to almost irreducible levels. The figures in your PNAS paper illustrate your point well.

Earlier you mentioned that eating less food reduces oxygen consumption and the load on the mitochondria. There is good evidence that calorie restriction -- cutting calorie intake by 30% or so while maintaining high micronutrient levels -- slows aging. Calorie restriction seems to lower the levels of undesirable sugar-damaged proteins called Advanced Glycosylation End-products (AGE). In Part II of this series, I would like to have you discuss how AGE's and oxidized proteins fits into the free radical picture.

Thank you Dr. Harman.

Copywright 1995 Reproduced with permission of the copywright owner. Whole Foods Magazine, WFC Inc. May not be distributed in any form without written permission.