EFFECTS OF CAFFEINE INGESTION ON NE KINETICS, FAT OXIDATION, AND ENERGY-EXPENDITURE IN YOUNGER AND OLDER MEN

Age-related differences in energy expenditure, fat oxidation, and nore pinephrine (NE) kinetics after caffeine ingestion were examined using a placebo-controlled double-blind study in 10 older (O, 65-80 yr) and 10 younger (Y, 19-26 yr) men who were moderate consumers of caffeine. Caffeine ingestion resulted in similar increases in Y and O men for pl asma caffeine levels (Y = 89 +/- 100 to 6,340 +/- 1,938 ng/ml, P < 0.0 5; O = 124 +/- 38 to 7,066 +/- 2,366 ng/ml, P < 0.05) and energy expen diture (Y = 11%, 1.38 +/- 0.15 to 1.52 +/- 0.22 kcal/min, P < 0.05; O = 9.5%, 1.15 +/- 0.13 to 1.26 +/- 0.20 kcal/min, P < 0.05). However, c affeine ingestion increased fatty acid concentrations (362 +/- 159 to 803 +/- 253 mu mol/l, P < 0.05) and tended to increase rate of appeara nce of fatty acids (624 +/- 376 to 1,394 +/- 1,331 mu mol/l, P = 0.07) in younger but not older men. Rates of fat oxidation and NE appearanc e and clearance did not significantly differ from baseline values in e ither group. In conclusion, older and younger men show a similar therm ogenic response to caffeine ingestion, whereas older men show a smalle r increase in fatty acid availability after a caffeine challenge. Thes e metabolic differences are not related to alterations in NE kinetics or fat oxidation.