AVPR2 gene and weight changes during triathlons

The arginine vasopressin receptor 2 (AVPR2) plays an important antidiuretic role in regulating water balance to maintain osmotic equilibrium. The aim of this study was to determine if there were any associations between single nucleotide polymorphisms (SNPs), within the AVPR2 gene, and changes in serum sodium concentrations and/or body weight (BW) in Ironman triathletes. Caucasian male triathletes who completed either the 2000, 2001 or 2006 South African Ironman Triathlons were genotyped (n=570) for at least one SNP. Pre- and post-race serum [Na+] (pre n=514; post n=423) and BWs (pre n=556; post n=552) were measured. Triathletes were divided into 3 groups according to their relative BW loss during the triathlon (BW loss of 0-3, 3-5 and >5%). There was a significant linear trend (p=0.010, x2=6.7) for the distribution of minor haplotypes GCT, GTC and GCC across the 3 BW loss groups. The >5% group had the highest percentage (4.7%) of triathletes with minor haplotypes followed by the 3-5% (3.6%) and 3-0% (0%) groups. In conclusion, the minor haplotype constructs of AVPR2 SNPs were associated with larger BW losses during the Ironman Triathlons. This finding supports a possible genetic contribution to BW loss during endurance exercise events acting through the argine vasopression system.