Life-Span Extension

Interventions that lead to a longer life span have been sought for ages. There is a huge amount of money to be made by selling over-the-counter drugs, dietary supplements, and nutraceuticals that claim some effect on life extension. Numerous companies and scientists are trying to develop dietary interventions that will prolong life. As of this writing however, there is no scientifically validated dietary supplement that has a significant effect on human longevity. One should be very careful before purchasing any agents that propose to extend longevity, and even more careful before consuming such a product. The FDA does not regulate dietary supplements, health foods, and nutraceuticals, and some of these agents could have a significant negative effect on one's health; others may be addictive.

Limiting total food intake, however, does have some beneficial effect. Around 1930, Clive McCay discovered that feeding rats a diet complete in vitamins and minerals, but low in total calories, resulted in a prolonged period of life. Since then, numerous studies have observed life extension in a variety of different species, both mammals and invertebrates, and the effects of caloric restriction (CR) on extending life span have been widely validated. There is anecdotal evidence that humans who practice CR are healthier and may have longer life spans; unfortunately, few people have the ability to eat 40 percent less than that eaten by the average person every day, for the rest of their lives. At least one start-up biotech company is attempting to overcome this problem using pharmaceuticals that will mimic the effect of CR.

Scientifically, caloric restriction (also called dietary restriction or food restriction) refers to the method of extending mean and maximal life span by reducing caloric intake of a test animal. This is the only widely validated means of life extension in mammals. (Genetic methods and drug interventions are beginning to be studied in invertebrates.) CR is not starvation, but a reduction in caloric intake that typically results in consumption of only about 60 percent of the normal ad libitum diet. Numerous physiological functions are changed by CR; indeed, it is difficult to find a change associated with aging that is not slowed by CR. This has been one of the real difficulties in studying CR, for almost everything responds. Typical CR animals look and behave much younger than their chronological age would suggest, and this is true at the organ, cellular, and molecular levels. CR works best if the animal is restricted early in life (just after puberty), but even CR initiated late in life can have an effect on longevity that is almost proportional to the amount of time the animal is on CR. A typical CR mouse or rat lives about 30 percent longer and is much more lean and active at later stages of life. However, CR is often associated with reproductive sterility.

It has been quite difficult to reliably study CR in humans, or to convince people to initiate a CR diet for themselves. Numerous proponents have tried to maintain CR for themselves, but the results are not systematic or generally convincing. The National Institutes of Health (NIH) is currently funding CR research on macaques and rhesus monkeys to see if the observations made in rodents can be extended to primates. The results seem to suggest that CR works in primates as well.