This study was designed to investigate the effects of aging and food intake on the serum beta-carotene (BC) response curve in humans. Ten elderly (71 +/- 4 years) and 17 young (28 +/- 7 years) healthy females were given 15 mg BC with a semi-solid test meal devoid of BC and vitamin A. All the elderly and 10 young subjects (control A) received a test meal of 500 kcal while the remaining 7 young subjects (control B) were given 700 kcal. Subsequently, blood was drawn hourly for 8 h and again at 24 and 48 h. Serum carotenoids and retinoids were measured by HPLC and triglycerides (TG) and cholesterol by enzymatic methods. Small intestinal transit time was determined in the elderly and in control group A by a breath hydrogen test following ingestion of lactulose (12 g) with the test meal. The area under the absorption curve (AUC) of serum BC over the first 8 h was higher in the elderly subjects than in either control group A or B (P less than 0.001). The slopes of the BC and TG curves were significantly higher as compared to control A, but similar to control B. There was a positive correlation between the ascending slopes of the BC and TG absorption curves of all groups (P less than 0.001). The AUC of the retinyl ester serum response of the elderly group was greater than that of control A (P less than 0.001). The slope of this curve was steeper (P less than 0.01) in the elderly group as compared to control A, but was similar to control B. Intestinal transit time was similar in all groups. In young subjects, the larger test meal of control group B appeared to increase the rate of absorption of BC. These data indicate that the rate of intact BC absorption and its conversion to retinyl esters may be enhanced in old age as compared to younger subjects receiving the same amount of food. Age-related alterations of enterocytes and the intestinal lumen could account for this phenomenon.