Restricting Calories Boosts the Immune System

And that may be a key to a longer life, study with monkeys suggests

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By Steven Reinberg
HealthDay Reporter

FRIDAY, Dec. 8, 2006 (HealthDay News) -- New research with rhesus monkeys appears to shed some light on why restricting calories may extend life spans.

Limiting consumption of calories seems to boost key infection-fighting cells in the immune system, the researchers say.

"The key finding is that in a primate species, which is very similar to ourselves, there is a very remarkable effect on the maintenance of the immune system with caloric restriction," said lead researcher Dr. Janko Nikolich-Zugich, a senior scientist at Oregon Health & Science University's Vaccine and Gene Therapy Institute.

As people age, changes in the immune system dramatically increase susceptibility to infectious diseases. So-called T cells, which make up an important component of the immune response, appear to be the part of the immune system most affected by aging, the researchers said.

In other studies, calorie restriction has been shown to reduce the aging of the immune system in rats. And calorie restriction has also been shown to increase the life span of yeast, worms, flies, zebrafish, and spiders. This same benefit may also hold true for monkeys, the researchers said.

"Under long-term caloric restriction, that was started in young adult monkeys, there is a very remarkable way of preserving both the form and the function of the immune system, which will result in much better resistance to infectious disease," Nikolich-Zugich said.

The study results are published in this week's issue of the Proceedings of the National Academy of Sciences.

In the 42-month study, Nikolich-Zugich and his colleagues found that calorie restriction improved the maintenance and production of T cells in 13 rhesus monkeys, 18 to 23 years of age, whose calories were restricted, compared with 28 monkeys who ate a normal diet.

The researchers found that calorie restriction improved T cell function and reduced the production of inflammatory compounds. These findings suggest that limiting calories can delay immunological aging, and, in turn, life span maybe increased by providing longer-term resistance to infectious diseases.

The estimated life span of rhesus monkeys is 25 years, so the monkeys in the study were the human equivalent of 60 to 70 years old. Those on a calorie-restricted diet were fed 30 percent less than the control animals.

Nikolich-Zugich said that people who restrict the number of calories they take in may also live longer because their immune system is "better and stronger." He also said it may be possible to find a drug that mimics calorie restriction that could improve the immune system. "Then, you would not fear viruses," he added.

Nikolich-Zugich is careful to note that improvement in the immune system is only one aspect of calorie restriction that extends life. "I don't think that it is solely the effect on the immune system," he said. "It is likely it is one of the important contributors. Calorie restriction has a beneficial effect on many different cells and tissues."

One expert thinks that strengthening the immune system is an important key to extending life.

"These results support the growing body of evidence that the beneficial effects of calorie restriction may be mediated through an anti-inflammatory mechanism," said Todd E. Morgan, a research associate professor at the University of Southern California's School of Gerontology.

The crucial next step will be to determine the molecular mechanism underlying calorie restriction's anti-inflammatory actions, Morgan said.

The monkeys in the project were part of an ongoing study of aging and calorie restriction in rhesus monkeys, conducted by the U.S. National Institute on Aging at the Primate Unit of the U.S. National Institutes of Health Veterinary Research Program.

More information

The U.S. Centers for Disease Control and Prevention can tell you more about healthy aging.

SOURCES: Janko Nikolich-Zugich, M.D., Ph.D., senior scientist, Vaccine and Gene Therapy Institute, Oregon Health & Science University, Beaverton; Todd E. Morgan, Ph.D., research associate professor, School of Gerontology, University of Southern California, Los Angeles; Dec. 4-8, 2006, Proceedings of the National Academy of Sciences

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