The association between the val/ala-55 polymorphism of the uncoupling protein 2 gene and exercise efficiency

BACKGROUND: Energy expenditure may partly be determined by genetic variatio ns in uncoupling proteins. We have previously found an increased physical a ctivity but a similar 24-h energy expenditure (EE) in subjects with the val /val-55 UCP2 genotype compared to those with the ala/ala genotype which ind icates that the val-55 allele is statistically associated with a higher met abolic efficiency. DESIGN: EE during bicycling was determined by indirect calorimetry at three different loads (30, 40 and 60% of VO2max in eight subjects with the val/v al-55 genotype (35 +/- 6 y weight = 76.8 +/- 13.6 kg, VO2max = 2.79 +/- 0.7 1 l/min) and eight subjects with the ala/ala-55 genotype (37 +/- 3 y, weigh t = 78.3 +/- 16.5 kg, VO2max = 2.66 +/- 0.41 l/min). RESULTS: Incremental exercise efficiency across the three different work le vels was higher in the val/val (25.3%, c.i. 24.2-26.4%) than in the ala/ala (23.6%, c.i. 22.5-24.7%) genotype P < 0.05. Cross exercise efficiency at 4 0% VO2max was higher in the val/val (15.3 <plus/minus> 0.6%) than in the al a/ala (13.5 +/- 0.4%) group. CONCLUSION: As the val/ala-55 polymorphism is located in a domain of the pr otein without any known function, the different exercise efficiency between the two genotypes most likely reflects a linkage disequilibrium with a fun ctionally significant polymorphism in UCP2 or in the neighbouring UCP3 gene . The study suggests that variations in the UCP genes may affect not only b asal metabolic rate but also influence energy costs of exercise.