Dietary protein, life-span, and biochemical variables in female mice.

The 50% mortality of female C57BL/6J mice fed ad libitum a diet which contained 26% or 4% casein, was 23.5 and 28 mo., respectively. Diet did not markedly affect the age-associated changes in the collagen content of the extractability of collagen of skin. In general, the activities of enzymes based on DNA were low in the restricted animals.