Iron status and stores decline with age in Lewis rats

In the context of a larger study examining the interaction of vitamin A (VA) status and age on immune function, we examined age-related changes in hematologic and iron status variables in male Lewis rats. Animals were fed a nutritionally adequate purified diet containing either 0.35 (marginal), 4.0 (control) or 50 (supplemented) mg retinol equivalents (as retinyl palmitate) per kg of diet from the time of weaning until killing at 8-10 (middle-aged) or 20-22 (old) mo of age. Neither VA nor VA and age interaction effects were significant for most iron variables examined. After controlling for body weight, old rats had significantly lower hemoglobin, hematocrit and plasma iron than middle-aged rats. This decrease in hematologic and transport iron variables was not accompanied by a shift of iron into other storage compartments. Old rats also had significantly lower total iron content and iron concentration in liver, spleen and bone marrow. Hemosiderin iron in marrow smears correlated significantly (r = 0.43-0.76, P < 0.05) with chemical estimates of iron in storage, transport and functional pools. Old rats also tended to have less stained iron in femur marrow smears. Thus, body iron in functional, transport and storage compartments, namely the liver, spleen and bone marrow, were significantly lower in old than in middle-aged rats. Although iron stores and status are usually considered to increase with advancing age, our data show a consistent pattern of lower hematologic and storage iron variables in old than in middle-aged Lewis rats. Future research is indicated to understand the biology and functional consequences of the observed age-associated decline in body iron.