Seven groups of mice were maintained on different dietary programs varying with respect to restriction at various stages of life. Restriction was associated with less age-related decline in T-dependent immunological function and a slight but significant lowering of body temperature. The best mean and maximum survival and the lowest late-life mortality rate was found in the group restricted throughout life, but restriction during any part of the lifespan enhanced survival to some degree. The mean life spans of tumor-bearing animals tended to be greater in restricted than in nonrestricted groups, corresponding to an age-decelerating effect. Tumor frequency varied with the period of life during which restriction took place and was not always decreased in restricted animals. These latter results suggest that the mechanisms whereby dietary restriction influences the aging rate and tumor susceptibility may not be entirely identical.

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Functional immune changes were monitored in populations of the long-lived C57BL/6J strain of mice which were subjected to dietary restriction from time of weaning or subjected to such restriction both before and after weaning, along with the appropriate control populations. Responses to T and B cell mitogens (PHA, Con-A, pokeweed, bacterial lipopolysaccharide, and PPD), to injected sheep red blood cells, and measurement of skin allograft rejection rates were followed. Early in life, restricted mice appear immunosuppressed, as judged by all these parameters. Skin allograft rejection remained suppressed until relatively late in life. Other responses tended to reverse from the earlier pattern; by mid-life restricted mice responded better than controls. Dietary restriction profoundly affects the immune system. Mice on such regimes display anatomic and certain immune functional changes which suggest that the immune system may mature less rapidly and stay ‘younger’ longer than in the controls. Furthermore, dietary restriction results in prolongation of life span.

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