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 variations in uncoupling proteins. We have previously found an increased physical activity 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 indicates that the val-55 allele is statistically associated with a higher metabolic 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/val-55 genotype (35 +/- 6 y weight = 76.8 +/- 13.6 kg, VO2max = 2.79 +/- 0.71 l/min) and eight subjects with the ala/ala-55 genotype (37 +/- 3 y, weight = 78.3 +/- 16.5 kg, VO2max = 2.66 +/- 0.41 l/min). RESULTS: Incremental exercise efficiency across the three different work levels 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 40% VO2max was higher in the val/val (15.3 <plus/minus> 0.6%) than in the ala/ala (13.5 +/- 0.4%) group. CONCLUSION: As the val/ala-55 polymorphism is located in a domain of the protein without any known function, the different exercise efficiency between the two genotypes most likely reflects a linkage disequilibrium with a functionally significant polymorphism in UCP2 or in the neighbouring UCP3 gene. The study suggests that variations in the UCP genes may affect not only basal metabolic rate but also influence energy costs of exercise.