Speedy D B, Noakes T D, Rogers I R, Thompson J M, Campbell R G, Kuttner J A, Boswell D R, Wright S, Hamlin M
Sportsmed, Christchurch, New Zealand.
Med Sci Sports Exerc. 1999 Jun;31(6):809-15. doi: 10.1097/00005768-199906000-00008.
Hyponatremia ([plasma sodium] <135 mmol x L(-1)) is a potentially serious complication of ultraendurance sports. However, the etiology of this condition is still uncertain. This observational cohort study aimed to determine prospectively the incidence and etiology of hyponatremia in an ultradistance triathlon.
The subjects consisted of 605 of the 660 athletes entered in the New Zealand Ironman triathlon (3.8-km swim, 180-km cycle, and 42.2-km run). Subjects were weighed before and after the race. A blood sample was drawn for measurement of plasma sodium concentration after the race.
Complete data on pre- and postrace weights and plasma sodium concentrations were available in 330 race finishers. Postrace plasma sodium concentrations were inversely related to changes in body weight (P = 0.0001). Women (N = 38) had significantly lower plasma sodium concentrations (133.7 vs 137.4 mmol x L(-1); P = 0.0001) than men (N = 292) and lost significantly less relative weight (-2.7 vs -4.3%; P = 0.0002). Fifty-eight of 330 race finishers (18%) were hyponatremic; of these only 18 (31%) sought medical care for the symptoms of hyponatremia (symptomatic). Eleven of the 58 hyponatremic athletes had severe hyponatremia ([plasma sodium] < 130 mmol x L(-1)); seven of these 11 severely hyponatremic athletes were symptomatic. The relative body weight change of the 11 severely hyponatremic athletes ranged from 2.4% to +5%; eight (73%) of these athletes either maintained or gained weight during the race. In contrast, relative body weight changes in the 47 athletes with mild hyponatremia ([plasma sodium] 130-134 mmol x L(1)) were more variable, ranging from -9.25% to +2.2%.
Hyponatremia is a common biochemical finding in ultradistance triathletes but is usually asymptomatic. Although mild hyponatremia was associated with variable body weight changes, fluid overload was the cause of most (73%) cases of severe, symptomatic hyponatremia.
低钠血症（血浆钠浓度＜135 mmol/L）是超长耐力运动潜在的严重并发症。然而，该病症的病因仍不明确。这项观察性队列研究旨在前瞻性地确定超长距离铁人三项赛中低钠血症的发生率和病因。
研究对象包括参加新西兰铁人三项赛（3.8公里游泳、180公里自行车骑行和42.2公里跑步）的660名运动员中的605名。在比赛前后对受试者进行称重。比赛结束后采集血样以测定血浆钠浓度。
330名完赛者有完整的赛前和赛后体重及血浆钠浓度数据。赛后血浆钠浓度与体重变化呈负相关（P = 0.0001）。女性（n = 38）的血浆钠浓度（133.7 vs 137.4 mmol/L；P = 0.0001）显著低于男性（n = 292），且相对体重减轻显著较少（-2.7% vs -4.3%；P = 0.0002）。330名完赛者中有58名（18%）患有低钠血症；其中只有18名（31%）因低钠血症症状寻求医疗护理（有症状）。58名低钠血症运动员中有11名患有严重低钠血症（血浆钠浓度＜130 mmol/L）；这11名严重低钠血症运动员中有7名有症状。11名严重低钠血症运动员的相对体重变化范围为-2.4%至+5%；这些运动员中有8名（73%）在比赛期间体重维持不变或增加。相比之下，47名轻度低钠血症（血浆钠浓度130 - 134 mmol/L）运动员的相对体重变化更具多样性，范围为-9.25%至+2.2%。
低钠血症是超长距离铁人三项运动员常见的生化表现，但通常无症状。尽管轻度低钠血症与体重变化多样有关，但液体超负荷是大多数（73%）严重有症状低钠血症病例的病因。
