Background: Phosphate supplementation has been used in an effort to enhance athletic performance by increasing erythrocyte 2,3-bisphosphoglycerate levels ([2,3-BPG]) and hence improve oxygen offloading from haemoglobin. Claimed effects of phosphate loading upon both exercise performance and erythrocyte [2,3-BPG] are inconsistent, and the basis of any change in [2,3-BPG] is unknown.
Methods: We analysed plasma inorganic phosphate concentration ([P(i)]) and erythrocyte [P(i)] and [2,3-BPG] in venous blood samples from 12 healthy subjects. We re-examined a subset of five of these subjects after 7 days of phosphate loading.
Results: There were significant positive correlations between plasma [P(i)] and erythrocyte [P(i)] (r(2)=0.51, p=0.009) and between erythrocyte [P(i)] and [2,3-BPG] (r(2)=0.68, p<0.001). Following phosphate loading, there was a 30% increase in plasma [P(i)] (1.02+/-0.22 to 1.29+/-0.15 mmol/l (mean+/-S.D.), p=0.03) and a 25% increase in erythrocyte [2,3-BPG] (6.77+/-1.12 to 9.11+/-1.87 mmol/l cells, p=0.03). There is no relation between [2,3-BPG] and plasma [P(i)].
Conclusions: Phosphate loading increases both plasma and erythrocyte phosphate pools and the rise in [2,3-BPG] is probably a consequence of the rise in cell [P(i)].