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Review

Peran natrium dalam cairan Homeostasis dengan latihan

Rick L. Sharp, PhD

Latihan Fisiologi laboratorium, departemen kesehatan & manusia kinerja, Iowa State University, Ames, Iowa

Kata kunci: natrium, cairan, Hiponatremia Gejala, latihan, aktivitas fisik, panas kelelahan

Makalah ini memberikan tinjauan terhadap sastra terkini mengenai efek interaktif natrium dan cairan

Penelanan dalam menjaga homeostasis fluida selama dan mengikuti paparan panas dan latihan. Berat berkeringat

selama latihan yang dikombinasikan dengan panas eksposur umumnya menghasilkan cairan defisit sesuai dengan 1 8% kerugian dalam

tubuh massa. Dengan demikian, banyak perhatian telah difokuskan pada pengembangan fluida penggantian panduan dan

produk untuk orang-orang yang aktif. Baru-baru ini, telah ada laporan lebih sering kasus Hiponatremia Gejala di antara

individu yang cenderung over-ingest air selama latihan yang berlangsung lebih dari empat jam, dan masuknya natrium

klorida dalam minuman fluida penggantian sering dianjurkan sebagai sarana potensi untuk mengurangi risiko

Hiponatremia Gejala. Meskipun Hiponatremia Gejala tidak cenderung menjadi faktor risiko utama untuk populasi umum,

daya tahan ultra-atlet dan orang-orang dengan aktivitas fisik pekerjaan dan eksposur panas mungkin akan mendapat keuntungan dari inirekomendasi. Penggantian fluida defisit setelah latihan dan panas eksposur daerah lain yang telah menerima

perhatian yang cukup besar. Penelitian di daerah ini menunjukkan bahwa jika air dikonsumsi, volume tertelan perlu

melebihi defisit fluida sekitar 150% untuk mengkompensasi kencing kerugian yang akan terjadi dengan air

Penelanan. Dimasukkannya natrium klorida dan lain larutan dalam minuman rehidrasi mengurangi kehilangan air kencing,

menuju pemulihan lebih cepat fluid balance. Data yang disajikan dalam makalah ini yang menyarankan diukur

interaktif hubungan antara natrium konten dan cairan volume dalam mempromosikan cepat sembuh dari fluid balance

setelah latihan dan dehidrasi termal-induced.

PENGENALAN

Dalam 1960 s itu tidak jarang untuk menemukan garam tablet

dispenser di ganti kamar di berbagai tempat olahraga. Ini adalahkarena dari keyakinan luas yang berlebihan kerugian sehingga-

dium keringat selama aktivitas fisik dapat menyebabkan pemiskinan

natrium dan mengakibatkan kram panas. Penelitian berikutnya,

Namun, menunjukkan bahwa keringat hipotonik dan natrium

konsentrasi lebih rendah daripada plasma. Temuan ini mengakibatkan

kesadaran bahwa nutrisi yang hilang dalam kelimpahan yang terbesar selama

latihan dalam panas adalah air daripada natrium. Lebih lanjut re-

pencarian dikonfirmasi menemukan ini dengan menunjukkan bahwa selama latihan

dalam kondisi panas dan lembab menyebabkan peningkatan dalam plasma

konsentrasi natrium [1], yang menyiratkan bahwa air penggantian mungkin

lebih penting daripada natrium penggantian selama exertional

stres panas.Dengan popularitas berjalan di 1970� s, itu menjadi

jelas bahwa penyakit panas merupakan risiko utama untuk orang-orang

berjalan di lingkungan yang panas dan lembab. Pedoman untuk fluida

penggantian dikembangkan dan bersama medis com-

munity, ras penyelenggara, dan untuk masyarakat umum. Khusus

minuman yang dikembangkan oleh perusahaan-perusahaan makanan untuk men

karbohidrat dan elektrolit penggantian dan dirancang untuk

digunakan sebelum, selama dan setelah latihan untuk membantu memenuhi

peningkatan tuntutan untuk nutrisi ini dalam melaksanakan publik.

Komposisi Olahraga minuman disesuaikan selama

30 tahun dalam menanggapi baik temuan-temuan penelitian dan rasa pref-

erences. Tujuan dari makalah ini untuk meninjau baru-baru ini

literatur ilmiah mengenai natrium keseimbangan dan hubungan-

kapal ke hidrasi selama dan setelah latihan, mi-

larly ketika dilakukan di bawah tekanan lingkungan panas.

AIR DAN NATRIUM KERUGIAN

SELAMA LATIHAN

Keringat produksi selama latihan dalam panas tergantung pada

latihan intensitas, durasi, pakaian, status hidrasi

Alamat cetak ulang permintaan: Rick L. Sharp, Ph.D., 250 Forker bangunan, departemen kesehatan & manusia kinerja, Iowa State University, Ames, IA 50011. E-mail:

[email protected]

Journal of American College of Nutrition, Vol. 25, No. 3, 231S 239S (2006)

Diterbitkan oleh American College of Nutrition

231S

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individu, panas-acclimation individu dan environmen-

Tal kondisi [2� 5]. Saat melakukan aktivitas fisik tinggi

lingkungan suhu, Penguapan keringat dari terkena

kulit adalah mekanisme utama untuk hilangnya panas. Apakah hilangnya panas

tidak cocok untuk tingkat metabolisme panas produksi (intensitas

latihan), penyimpanan panas tubuh naik dan inti suhu dapat

cepat mencapai tingkat berbahaya. Menjaga kapasitas tinggi untuk

keringat produksi karena itu penting dalam thermoregulation dan

pencegahan penyakit panas. Selama intensitas tinggi atletik,

keringat harga hingga 3 L\/hr mungkin di bawah panas dan lembab

kondisi [6,7]. Hal ini menyebabkan hilangnya tubuh air atau dehy-

dration setara dengan 1 8% dari tubuh massa. Digabungkan dengan keringat

konsentrasi natrium rata-rata berkisar antara 40� 60

mEq\/L [6 9], seperti keringat harga dapat mengakibatkan natrium pemiskinan

tingkat sekitar 150 mmol\/hr dengan natrium tambahan kerugian dalam

produksi air seni.

Sebuah studi oleh Mao et al. diukur elektrolit keringat dan

kencing elektrolit konsentrasi dan ekskresi dalam 13 remaja

Pemain sepak bola (16 18 thn) selama 1 jam sepak bola praktek con-

menyalurkan dalam panas (32 37C, kelembaban relatif 30 50%) pada delapan

hari [10]. Konsentrasi natrium berarti keringat adalah 55 mmol\/L.

Rata-rata keringat kerugian selama sesi 1 jam latihan adalah 1.54 l

(SD 2.06 L). Keringat dihitung hilangnya natrium rata-rata

mmol 82 (SD 62 mmol). Kencing hilangnya natrium rata-rata 110

mmol (SD 36 mmol). Dengan demikian rata-rata natrium ekskresi ac-

menghitung untuk oleh keringat dan saluran kemih ekskresi adalah 192 mmol (tabel

1). Karena tidak ada data dietary intake dilaporkan untuk mata pelajaran ini,

natrium dan fluid balance bisa tidak dihitung. Demikian pula, tidak ada

data yang diperoleh untuk menilai kinerja baik atau fisiologis

konsekuensi dari kerugian ini cairan dan elektrolit. Meskipun demikian,

observasi ini menyarankan kerugian besar natrium dan air

selama latihan dalam panas.Dimungkinkan bahwa metode pengumpulan keringat digunakan oleh Mao

et al. berlebihan seluruh tubuh natrium kerugian dalam keringat karena

untuk variasi regional dalam konsentrasi natrium keringat [11,12].

Belajar di Mao et al., keringat dikumpulkan dari punggung dan

dada subjek selama 5 menit selama sesi latihan.

Konsentrasi natrium diukur 55 mmol\/L mirip

konsentrasi Na keringat dikumpulkan oleh Shirreffs menggunakan

seluruh tubuh washdown metode [12]. Shirreffs et al. diukur

keringat konsentrasi natrium 51.6 mmol\/L selama latihan

memproduksi dehidrasi 2% dari subyek. Oleh karena itu tidak mungkin

data yang diperoleh oleh Mao et al. yang terlalu berlebihan.

Dalam sebuah studi oleh Sanders et al. [13], air dan natrium kerugian

diukur selama 4 hr bersepeda latihan pada 20 C pada latihan

intensitas setara dengan 55% dari puncak VO2. Selama latihan

mata pelajaran tertelan 3.85 l elektrolit karbohidrat 8 %

minuman yang mengandung 5, 50, atau 100 mmol\/L natrium. Keringat kerugian

rata-rata antara 3,7 dan 3,9 l untuk masing-masing dari cobaan. Natrium

konsentrasi keringat berkisar 43� 48 mmol\/L, memproduksi

kerugian natrium keringat antara 150 dan 190 mmol atas 4 hr

latihan. Dikombinasikan dengan natrium kencing kerugian, mata pelajaran

mengalami negatif natrium keseimbangan 198 mmol ketika

menelan 5 mmol\/L Na minuman, 36 mmol ketika menelan

50 mmol\/L Na minuman, dan mengalami natrium positif

keseimbangan 159 mmol ketika menelan minuman yang mengandung

mmol 100\/L natrium (Fig. 1). Selain untuk meyakinkan positif

natrium keseimbangan di seluruh latihan, konsumsi minuman

mengandung 100 mmol\/L natrium mengurangi total cairan yang hilang selama

latihan dibandingkan dengan minuman lain. Perhitungan

perubahan kompartemen air mengungkapkan kerugian signifikan fluida

dari ECF) 1.1 L) 5 mmol\/L sodium sidang, tidak ada perubahan dalam

ECF di 50 mmol\/L natrium pengadilan, dan perluasan ECF

volume) 0.5 L) sodium mmol 100\/L percobaan. Meskipun

lebih baik pemeliharaan hidrasi status di 50 dan 100

mmol\/L natrium cobaan, tanggapan kardiovaskular (misalnya denyut jantung

Respon) adalah serupa di antara tiga persidangan.

HIPONATREMIA GEJALA

Selama 20 tahun terakhir, orang-orang yang terlibat dalam durasi panjang

latihan daya tahan di panas telah disarankan untuk minum sebagai

banyak cairan mungkin selama latihan untuk mencegah dehydra-

tion, menjaga respon berkeringat dan dengan demikian memelihara

Pengatur suhu tubuh kapasitas [14]. Sayangnya, saran ini memiliki

mengakibatkan peningkatan atau setidaknya pengakuan Hiponatremia Gejala di banyak atlet bersaing dalam peristiwa ini [15 19]. Hyponatre-

Mia dapat menyebabkan karena hilangnya berlebihan natrium karena

berat berkeringat tanggapan, atau alternatif, karena yang pengenceran

plasma natrium sebagai konsekuensi dari terlalu bersemangat hidrasi [16].

Berbagai rekomendasi untuk mencegah Hiponatremia Gejala

dibuat dalam literatur dan termasuk mengurangi penekanan pada

fluida Penelanan [20] dan\/atau meningkatkan kandungan natrium bev-

erages tertelan selama latihan [21 24].

Prevalensi Hiponatremia Gejala

Beberapa penulis telah dijelaskan kasus Hiponatremia Gejala dur-

ing ketahanan latihan dalam panas. Speedy et al. telah menerbitkan

terbesar berbasis bidang studi terjadinya Hiponatremia Gejala

Tabel 1. Cairan tubuh dan natrium kerugian selama 1 jam sepak bola praktek di antara remaja laki-laki

Tubuh massa

(kg)

Kehilangan cairan

(L)

Keringat [Na]

(mmol\/L)

Keringat Na

Kehilangan

(mmol)

Kencing Na

Kehilangan

(mmol)

Total Na

Kehilangan

(mmol)

Berarti 62,5 1.54 55 82 110 192

SE 6,8 0,57 27 62 36 �

Data berasal dari Mao et al. [10].

Natrium dalam cairan Homeostasis dengan latihan

232S VOL. 25, NO. 3









[18]. Dalam studi ini, 330 finishers perlombaan triathlon (6� 9

HR) dipelajari. Berdasarkan plasma natrium konsentrasi kurang

dari 135 mmol\/L, 58 (18%) dari finishers yang hyponatre-

Mikha sebelas mata pelajaran ini yang digambarkan sebagai sangat hy-

ponatremic) 130 mmol\/L) dan tujuh ini symp -

tomatic. Para penulis juga mencatat bahwa orang-orang subjek dengan

kasus-kasus yang paling parah Hiponatremia Gejala telah sedikit perubahan dalam tubuh

berat selama perlombaan, menyiratkan bahwa cairan yang berlebihan

menyebabkan Hiponatremia Gejala dalam sebagian besar kasus.

Penulis lain menyarankan Hiponatremia-Gejala itu hanya dapat

faktor risiko yang signifikan dalam luar biasa panjang durasi fisik aktivitas seperti maraton berlari dan triathlon berlangsung 4 jam

atau lebih. Noakes et al. [20] menunjukkan bahwa sebagian besar kasus

Hiponatremia Gejala diamati dalam para peserta kurang terlatih

Siapa yang mengambil jauh lebih lama untuk menyelesaikan lomba daripada atas

finishers. Durasi yang lebih lama dari latihan digabungkan dengan lebih besar

total fluida asupan sebagai akibat dari durasi yang lebih lama, karena itu

menempatkan orang-orang ini pada risiko lebih besar mengembangkan Hiponatremia Gejala.

Karena kasus Hiponatremia Gejala diinduksi latihan

sebagian besar terbatas pada upaya fisik luar biasa yang berlangsung lagi

dari 4 hr, Hiponatremia Gejala bukanlah cenderung sangat lebar-

menyebar di populasi umum yang terlibat dalam latihan

berlangsung kurang dari 2 jam per hari. Berbagai mekanisme telah

diajukan untuk menjelaskan pengembangan Hiponatremia Gejala dalam beberapa

individu. Penyebab ini termasuk cairan yang berlebihan atau pengenceran

efek [17], berlebihan natrium kehilangan selama latihan [21], dan

tidak pantas tanggapan dari arginin-vasopresin mengarah ke mantan

cessive retensi cairan tertelan [25]. Temuan lebih besar

prevalensi Hiponatremia Gejala di antara wanita menunjukkan baik

efek biologis seks pada fluida homeostasis atau perilaku berbeda-

ences antara pria dan wanita yang mungkin menyebabkan perempuan untuk dapat

lebih sesuai dengan saran untuk minum cairan sebanyak mungkin

selama latihan daya tahan [27].

Pencegahan Hiponatremia Gejala

Jika fluida overload adalah kontributor penting untuk mengembangkan-

ment Hiponatremia Gejala, orang akan berharap plasma natrium con-

centration jatuh selama latihan sebanding dengan volume

natrium rendah atau tidak ada cairan tertelan. Vrijens dan Rehrer [24]

memeriksa pertanyaan ini oleh merekrut subjek laki-laki 10 untuk exer-

cise untuk 3 hr di ruang lingkungan disimpan di 34 C. Themata pelajaran melakukan latihan ini pada dua hari yang terpisah; sekali

Sementara menelan bebas natrium air setiap 15 menit untuk mencocokkan

kehilangan cairan, dan sekali sementara menelan natrium komersial-

mengandung (18 mmol\/L Nakarbohidrat 63 g\/L, 3 mmol\/L

kalium) minuman untuk mencocokkan kehilangan cairan. Selama air

Penelanan konsentrasi natrium sidang, rata-rata plasma menolak

dari 140 mmol\/L sebelum latihan untuk 134 mmol\/L pada akhir

latihan (Fig. 2). Dalam sidang, karbohidrat-elektrolit plasma

konsentrasi natrium tidak mengurangi secara signifikan (140

mmol\/L sebelum latihan, 138 mmol\/L di akhir latihan). The

penulis menyimpulkan bahwa Hiponatremia Gejala diperbolehkan bahkan ketik

asupan cocok kehilangan cairan selama durasi panjang berolahraga ketikanatrium tidak termasuk dalam minuman pengganti fluida.

Penulis lain juga merekomendasikan dimasukkannya natrium

dalam minuman dikonsumsi selama latihan [7,22,23,26]. Gisolfi

[26] dianjurkan bahwa orang-orang yang berolahraga untuk 1 3 hr harus

mengkonsumsi antara 800 1600 ml\/hr cairan yang mengandung 10 20

mmol\/L natrium dan bahwa orang-orang yang berolahraga untuk lebih dari 3 jam

harus mengkonsumsi 500 1000 ml\/hr cairan yang mengandung 20 30

mmol\/L natrium. Lutkemeier et al. [22] menyarankan bahwa saline

Penelanan sebelum latihan dapat membantu melestarikan plasma volume

dan dapat mengakibatkan perubahan yang bermanfaat dalam latihan daya tahan

kinerja. Dalam review artikel yang diterbitkan oleh Rehrer [7] inclu-

Sion natrium dalam minuman pengganti fluida pada konsentrasi

berkisar antara 30 dan 50 mmol\/L disarankan sebagai kemungkinan

bermanfaat bagi orang-orang yang terlibat dalam panjang durasi latihan (3 hr ata

lebih) dalam panas.

Konsisten dengan hipotesis yang berlebihan natrium kehilangan

Gambar 1. Natrium keseimbangan di ujung 4-jam latihan bersepeda di 20 C

(kering-bohlam) lingkungan. Uji mengulangi dengan menelan 3.85 l

8% karbohidrat-elektrolit minuman dengan 5, 50, atau 100

mmol\/L natrium konsentrasi. Diadaptasi dari Sanders et al. [13].

Fig. 2. Konsentrasi natrium plasma sebelum dan setelah 3-jam latihan di

34 C (kering bohlam) lingkungan dengan menelan air baik polos

pertandingan kehilangan cairan atau minuman elektrolit karbohidrat komersial untuk

cocok kehilangan cairan. Diadaptasi dari Vrijens dan Rehrer [24].

Natrium dalam cairan Homeostasis dengan latihan

JOURNAL OF AMERICAN COLLEGE OF NUTRITION 233S









the primary cause of exercise-induced hyponatremia, Hiller et

al. [21] suggested 1 2 g sodium ingestion per hour of exercise

to prevent hyponatremia. Assuming fluid ingestion of 1 liter per

hour to match fluid lost through sweating, this amount of

sodium requires a beverage containing 43 87 mmol/L sodium.

This recommendation is slightly higher than that recommended

by Rehrer and represents a sodium concentration roughly 2 4

times as high as that found currently in most commercial fluid

replacement beverages. Barr et al. argues that the reduced

palatability of such beverages would likely lead to less fluid

consumption among the general population and result in a

greater risk of dehydration [28].

There are also several studies that provide evidence that

sodium supplementation during exercise along with fluid re-

placement is not necessary [28 32]. Barr et al. had 8 subjects

perform 6 hr exercise at 55% VO2max in a heat chamber held

at 30C [28]. Each subject completed this exercise on separate

occasions to evaluate the possible effects of water ingestion,

water plus sodium (25 mmol/L), or no fluid. When the subjects

were not provided with fluid during the exercise, core temper-

ature and heart rate rose rapidly while plasma volume declined

throughout exercise. Under this condition, only one subject was

able to complete the full 6 hr exercise and the mean time of

exercise was 4.5 hr. The subjects who failed to complete the

exercise did so because heart rate exceeded 95% maximum

heart rate (n 1), core temperature exceeded 40C (n 1), or

volitional exhaustion (n 5). In the water and saline trials,

seven of the eight subjects completed the 6 hr of exercise.

There were no differences in either heart rate or core temper-

ature response between water and saline ingestion and both

trials resulted in smaller rise in these variables than was ob-

served when no fluid was ingested. Plasma volume droppedless when ingesting the saline beverage than when ingesting

water. Plasma sodium concentration decreased by small

amount in both the saline (change 3.0 mmol/L) and water

(change 3.9 mmol/L) trials but there were no significant

differences in plasma sodium concentration between these tri-

als. Calculation of overall sodium balance revealed a sodium

deficit in the water trial ( 207 mmol) that was significantly

larger than observed in the saline trial (91.3 mmol). Based on

these results, the authors concluded that sodium concentration

equivalent to that found in commercial sports drinks do not

prevent the fall in plasma sodium during exercise when fluid

intake matches fluid lost through sweating. They further sug-

gest that sodium replacement is not necessary in exercise

lasting less than 6 hr.

Based on these reviewed studies, it is apparent that inclusion

of sodium in fluid replacement beverages can offset some of

the losses of sodium that occur during prolonged and heavy

sweating. It is less clear that doing so will prevent hyponatre-

mia or that this improves either exercise performance or ther-

moregulation. As suggested by Sanders et al., however, sodium

ingestion likely preserves the plasma volume during exercise at

the expense of the intracellular fluid volume. What effect this

relative dehydration has on muscle metabolism and function

has not yet been studied. An additional finding common to

most of these studies is that even if sodium ingestion does not

affect plasma sodium concentration, it does reduce the sodium

deficit that occurs during prolonged exercise in the heat. This

may be significant for people who are involved in daily exer-

cise or occupations that involve prolonged physical activity in

hot, humid environments.

ROLE OF SODIUM INREHYDRATION AFTER EXERCISE

Despite efforts to replace fluid losses during exercise, mild

dehydration after exercise remains a common finding. Dehy-

dration equivalent to less than 2% loss of body mass is asso-

ciated with reduced performance and impaired thermoregula-

tion during subsequent exercise if the fluid deficit is not

corrected. Thus, considerable research has been devoted to

understanding the rehydration process and the role played by

sodium in restoring body fluids lost during prior exercise.

In studying rehydration after exercise-induced body water

loss, investigators have employed three models for rehydration:

allow subjects to drink fluids ad lib during the rehydration

period [33 35], prescribe fluid intake during the rehydration

period to match the fluid lost during the prior exercise [36 38],

and prescribe fluid intake in excess of the fluid lost in the prior

exercise [39 43]. The advantage of allowing ad lib rehydration

is that factors regulating thirst can be studied while the advan-

tage of prescribing fluid intake equal to fluid lost restores

plasma volume while total body water remains somewhat con-

tracted. The rationale for the approach that involves prescribingfluid intake in excess of that lost in the prior exercise is that

both plasma volume and total body water are restored by the

end of the rehydration period. Finally, there are also hybrid

models in which varied amounts of fluid and sodium content

are studied to allow for evaluation of independent effects of

sodium and fluid volume on the rehydration process.

Ad Libitum Rehydration

Nose et al. dehydrated six subjects by 2.3% using thermal

and exercise induced dehydration [34]. Over the next 3 hr,

subjects were seated in a thermoneutral environment and al-

lowed to rehydrate ad libitum using tap water (15C), placebo or

capsules containing NaCl to produce sodium concentration of

75 mmol/L. The purpose of this approach was to examine the

effect of sodium on drinking behavior and restoration of body

fluid compartments. Average fluid loss in the dehydration

period was 1550 ml and was followed by ingestion of 1100 ml

in the water trial and 1216 ml in the water plus sodium trial,

leaving the subjects in a fluid deficit after 3 hr of rehydration.

When urine production is subtracted from fluid ingestion, net

fluid gain during rehydration was 826 ml in the water trial and

Sodium in Fluid Homeostasis with Exercise

234S VOL. 25, NO. 3



1045 ml in the water plus sodium trial. Despite the persistent

negative fluid balance even after 180 min, plasma volume had

returned to pre-dehydration by 90 min of recovery in the water

plus sodium trial while plasma volume remained slightly below

the pre-dehydration level even at 180 min of recovery. Calcu-

lation of fluid compartment recovery based on chloride space

showed that by the end of the rehydration period, total body

water had recovered by 52% in the water trial and by 76% in

the water plus sodium trial. Recovery of intracellular fluid was

not different between water and water plus sodium trials. Both

ECF and PV were more completely restored in recovery in the

water plus sodium trial (84% and 100%, respectively) com-

pared with water only (44% and 77%, respectively). These

findings illustrate the following points: 1) thirst is inadequate to

assure complete recovery of total body water deficits likely due

to early restoration of plasma volume, thereby removing the

volume dependent dipsogenic drive, 2) the presence of sodium

in the rehydration beverage stimulates greater drinking likely

due to greater osmotic dipsogenic drive, 3) the presence of

sodium in the rehydration beverage accelerates the recovery of

extracellular fluid and plasma volume in particular, and 4)

sodium in the rehydration beverage reduces urinary losses of

water, allowing a greater fraction of the ingested fluid to be

retained. These findings were later confirmed by Wemple et al.

using a similar dehydration and rehydration protocol [35].

Rehydration with Fluid Intake Sweat Loss

Several studies have examined recovery of body water

losses after exercise by providing an amount of fluid to subjects

that is equal to the amount of water lost during the exercise as

a consequence of sweating. Most of these studies attempted toachieve complete rehydration within a relatively short period

lasting between 2 and 4 hours. The early study by Costill and

Sparks [36] dehydrated eight male subjects using intermittent

exposure to dry heat (70C) until 4% of body mass was lost.

Once the prescribed dehydration was reached, the men returned

to a thermoneutral environment to begin the rehydration period.

At the beginning of rehydration and at 15-min intervals the

subjects drank a volume of fluid equal to 7.7% of the volume

lost during the dehydration. This was continued for 3 hr so that,

by the end of the 3 hr rehydration period, the subjects had

ingested the same total volume of fluid as lost in dehydration.

The procedure was repeated once when ingesting plain water as

the rehydration fluid and once using a carbohydrate-electrolyte

(CE) drink for rehydration. The CE drink contained 22 mmol/L

sodium, 17 mmol/L chloride, 2.6 mmol/L potassium, 3.9

mmol/L phosphate, and 10.6 g/100ml glucose with osmolality

of 444 mOsm/L.

Urine production was significantly higher when subjects

rehydrated with water (602 ml) than when using the CE bev-

erage (367 ml). Despite drinking a volume of fluid equal to that

which was lost in dehydration these subjects were only able to

recover 62% of their body mass loss during the rehydration.

This was mostly due to urinary and insensible loss of water

during the rehydration period. Plasma volume had dropped by

an average of 12% with dehydration and 38% of this loss was

recovered during rehydration with water while 67% of the loss

in plasma volume was recovered when drinking the CE bever-

age. The authors concluded that the presence of electrolytes and

carbohydrate in the rehydration favored a more complete re-

filling of plasma volume, but that neither beverage was ade-

quate for completely restoring either plasma volume or total

body water when 100% of the dehydration volume is consumed

overa3hr period.

Rehydration With Fluid Intake > Fluid Loss

Based on the earlier observations of incomplete body water

restoration when either thirst regulates fluid intake or fluid

intake matches the fluid lost in the prior dehydration, most

recent studies have provided fluid in excess of that which was

lost in dehydration [39 43]. Authors recognized that additional

fluid was needed to offset the obligatory urinary losses, con-

tinued sweat water loss, and water loss through respiration.

These studies fail to demonstrate complete body water resto-

ration during rehydration lasting up to 6 hours unless the

ingested fluid is coupled with sodium ingestion. A convenient

method of providing both fluid and sodium during rehydration is

to select a rehydration beverage or food providing both fluid and

sodium with other nutrients (carbohydrate and potassium, e.g.)

that may be vital in restoring normal function after dehydration.

Maughan and Leiper [39] examined the role of varied

concentrations of sodium in the rehydration beverage in achiev-

ing euhydration after mild dehydration of approximately 2%.

Their approach involved ingestion of 150% of the fluid lostduring a 30 minute period after a dehydration protocol consist-

ing of intermittent cycling exercise in a 32C environment.

Recovery of physiological markers of dehydration was fol-

lowed for 5.5 hr after ingesting the rehydration beverages. The

four beverages compared included sodium concentrations of 2,

26, 52, and 100 mmol/L. Although the fluid intake was con-

siderably larger than used in the prior research, neither the 2

mmol/L nor 26 mmol/L beverages resulted in complete recov-

ery of body water (66% and 82% recovery of body mass loss,

respectively) (Fig. 3). Both of the higher sodium beverages

resulted in complete (100%) rehydration by the end of the 5.5

hr monitoring period.

In an ambitious study designed to assess the interactive

effects of both sodium content and volume of fluid ingested in

rehydration, Shirreffs et al. [41] rehydrated subjects using

either 50%, 100%, 150%, or 200% of the volume lost and each

of these volumes contained either low sodium (23 mmol/L) or

higher sodium (61 mmol/L) concentration. Based on the net

fluid balance presented, body water recovery was nearly com-

plete (91% for both) with the lower sodium fluid when con-

sumed in both 150% and 200% excess but was incomplete with

either 50% volume (39% recovery) or 100% volume (60%


JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION 235S



recovery) (Fig. 4). With the higher sodium content in ingested

fluid, recovery of the fluid deficit was complete with ingestion

of 150% of volume lost (107% recovery) while ingestion of

200% of volume lost resulted in a surplus of fluid (127%

recovery). Neither the 50% volume nor 100% volume fully

restored whole body fluid balance (38% recovery and 81%

recovery, respectively). Urine volume was positively related to

the volume of fluid ingested and inversely related to the content

of sodium in the rehydration beverage.

Multiple Regression of Sodium Concentration and

Fluid Volume

That recovery of total body water would depend on both the

sodium intake and the volume of fluid ingested may seem

intuitively obvious. The above reviewed studies provide an

evidentiary framework for quantifying this interactive effect.

Although each of these studies has compared rehydration be-

tween different volumes and between different intakes of so-

dium, there have been no attempts to use the combined data

from several studies in estimating the independent and interac-

tive contributions of fluid volume and sodium concentration to

the rehydration process. The data displayed in Table 2 summa-rizing the findings of several rehydration studies were therefore

used in a multiple regression analysis to assess the relative

contributions of sodium concentration and fluid ingestion. In

each study, the data that were presented in the published paper

were either used directly (when provided by the authors) or the

relevant data were calculated from other results reported by the

authors. For the purpose of this analysis, whole-body rehydra-

tion (dependent variable) was expressed as the percentage

recovery of the fluid loss that had occurred during the dehy-

dration protocol. The reported sodium concentration of the

rehydration solution and the volume of this solution were used

as independent variables. Initially, additional variables wereentered into the regression model but none of the other vari-

ables achieved statistical significance (p 0.05). The variables

which did not significantly contribute to the prediction of fluid

recovery included urine volume during dehydration (likely due

to colinearity with sodium concentration), body mass (due to

low range of body mass in the reported studies), and duration

of rehydration period (which ranged from 2 6 hr).

The final regression model included both sodium concen-

tration (mmol/L) of the rehydration fluid and volume of this

solution consumed during the rehydration period (ml) as sig-

nificant predictors of percent recovery of fluid balance (Table

3). The resulting regression equation was

% rehydration 22.7 0.406 * Na 0.021 * volume

In the example of a 75 kg person who dehydrates by 2.5% and

ingests 100% of the volume lost during rehydration, a sodium

concentration of approximately 93 mmol/L would be required

to achieve fluid balance within 6 hr. On the other hand, if fluid

intake is increased to 150% of that lost in prior dehydration, the

regression model predicts that full rehydration could be

achieved with a sodium concentration of approximately 50

mmol/L. However, it must be noted that the regression model

accounts for only 66% of the variance in body water recovery.

It is likely that additional variables including temperature of the

ingested fluid, presence of other electrolytes (potassium, cal-

cium, magnesium) and nutrients (carbohydrate, amino acids),

arginine vasopressin and aldosterone, and osmolality of the

rehydration fluid also play important roles but are not included

in this regression model. Thus the present analysis is incom-

plete but does support the contention that both fluid volume and

sodium concentration are important considerations in the se-

lection and/or design of optimal rehydration solutions.

Fig. 3. Percent recovery of fluid balance during a 5.5-hr rehydration

period in which fluid was ingested at a volume equal to 150% of the

fluid deficit that was incurred. Rehydration was compared between

beverages containing 2 100 mmol/L sodium. Adapted from Maughan

and Leiper [39].

Fig. 4. Percent recovery of fluid balance during 6-hr rehydration period

in which both volume and sodium concentration of beverage were

varied. Adapted from Shirreffs et al. [41].


236S VOL. 25, NO. 3



Rehydration with Food

One study from our laboratory [38] examined the question

of whether ingestion of food containing fluid and sodium is

effective in restoring fluid and sodium balance after a dehy-

drating bout of exercise and heat. Subjects were dehydrated by

2.5% using intermittent exposure to heat and exercise. Once the

prescribed fluid loss was achieved, subjects ingested 355 ml of

either chicken broth, chicken soup with noodles, a carbohy-

drate-electrolyte beverage, or tap water. Thereafter, the subjects

ingested an average of 290 ml water every 20 min so that total

fluid intake by 2 hr matched fluid loss. The decision to choose

Table 2. Summary of Papers Used in Multiple Regression to Describe Relationship between Fluid Volume and Sodium

Concentration of the Rehydration (RH) Solution

ReferenceBody Mass

(kg)

Change in Body

Mass (kg)

Volume Ingested

During RH (ml)

Sodium

Concentration

(mmol/L)

Urine Volume

(ml)

% Recovery of

Fluid Balance

Costill & Sparks 1973 [36] 71.7 2.74 2740 0 602 73

71.7 2.74 2740 60 367 73Maughan & Leiper 1995 [39] 71.8 1.36 2045 2 1350 66

71.8 1.36 2045 26 940 82

71.8 1.36 2045 52 610 100

71.8 1.36 2045 100 580 100

Maughan et al. 1996 [40] 66.1 1.36 2042 21 940 75

66.2 1.36 2042 21 935 73

Shirreffs et al. 1996 [41] 71.5 1.49 746 23 135 41

71.5 1.45 1448 23 493 69

71.5 1.50 2255 23 867 101

71.5 1.46 2927 23 1361 103

73.2 1.52 758 61 194 40

73.2 1.52 1522 61 260 83

73.2 1.50 2243 61 602 106

73.2 1.59 3180 61 1001 136

Shirreffs & Maughan 1998 [42] 69 1.27 1912 0 1182 5069 1.29 1938 25 970 69

69 1.31 1968 50 800 80

69 1.36 2035 100 578 101

Ray et al. 1998* [38] 72.0 1.80 1800 0 232 76

72.3 2.00 2000 21 310 76

72.0 1.80 1800 18 188 75

72.2 1.70 1700 35 231 78

Mitchell et al. 2000 [43] 79.6 2.26 2280 25 300 71

79.6 2.26 2280 50 180 104

79.6 2.28 3390 25 600 76

79.6 2.28 3390 50 540 101

* Sodium concentration calculated based on amount of sodium provided by ingestion of soup broth and soup diluted by additional water ingested during rehydration period.

Change in body mass from pre-dehydration to pre-rehydration.

Calculated as percentage recovery in body mass lost or net fluid balance depending on how the data were expressed in referenced paper.

Table 3. Multiple Regression of Percent Recovery of Fluid Balance as a Function of Both Volume and Sodium Concentration of

Fluid Ingested during Rehydration

Coefficient Std Error t P

Constant 22.70 9.17 2.48 0.020

Na conc 0.406 0.093 4.38 0.001

Volume 0.021 0.004 5.46 0.001

DF SS MS F P

Regression 2 7764 3882 23.9 0.0001

Residual 25 4055 162

Total 27 11819 438Y 22.7 0.406Na conc 0.021vol intake)

R 0.81 R 2 0.66

Data were extracted from references shown in Table 2.





these products was based on commercial availability to

consumers as well as their varied amounts of electrolytes and

osmolality. With regard to sodium intake, chicken noodle soup

and chicken broth treatments provided a total sodium ingestion

of 50 mmol and 39 mmol, respectively. This is considerably

less than the sodium intake associated with the prior studies in

which subjects ingested 150% of the fluid loss with a sodium

concentration of 50 100 mmol/L. Using the regression model

from above, it is expected that the chicken broth and the

chicken noodle soup treatments would not fully restore the

fluid deficit in 3 hr (estimated % rehydration 73% for both).

Measured fluid recovery was 76% and 78% for the chicken

broth and chicken noodle soup, respectively. Although total

body fluid balance was not fully recovered in rehydration,

plasma volume was fully restored with the chicken broth and

the chicken noodle soup trials, but not with either a commercial

carbohydrate-electrolyte beverage or with water.

These findings illustrate the importance of ingestion of

sodium during the rehydration period not only for encouraging

increased retention of ingested fluids but also for restoration of

the plasma volume, which can be re-filled ahead of total fluid

balance when sufficient sodium is provided either in the rehy-

dration drink or in food consumed during rehydration. In ad-

dition, these findings show that it may not be necessary to

include sodium in every aliquot of fluid ingested during rehy-

dration if sufficient sodium is provided early in the rehydration

period either as a constituent of fluid or food.

SUMMARY AND CONCLUSION

Both sodium and fluid ingestion play important roles inmaintaining health and physiological function during physical

activity in hot environments. Whether people engage in pro-

longed endurance exercise such as marathons and triathlons or

if they are involved in occupational heat exposure during

physical activity, it is important that both fluid and sodium are

provided to offset the losses in both nutrients that occur as a

consequence of heavy sweating. People involved in vigorous

exercise in hot environments lose up to 3 liters of water and 3.5

grams of sodium per hour through sweating. Preventing these

fluid and sodium deficits helps to maintain both performance

and thermoregulation in such environments. The evidence from

published literature shows that fluid intake during exercise in a

warm environment is absolutely essential to attenuate the rise

in core temperature. These studies also demonstrate that unless

sodium is provided in the fluid replacement beverage, fluid

intake that matches or exceeds fluid loss may cause hypona-

tremia in some individuals participating in at least 4 hr of

exercise. Thus, many authors now recommend sodium concen-

tration of 20 50 mmol/L in beverages consumed during the

physical activity.

In designing a nutritional strategy for recovery from exer-

cise and heat exposure that results in mild dehydration, the dual

and interactive roles of fluid and sodium intake should be

considered. This synergistic association between fluid volume

and sodium intake is reflected in recommendations to consume

fluid in excess of that lost during the prior exercise and to

include sodium to increase the retention of the ingested liquids

by minimizing urine production. The papers reviewed here

suggest that plasma volume can be fully restored before total

body water deficits are fully corrected when sodium intake is

consumed either as a component of the rehydration beverage

with sodium concentration of approximately 20 mmol/L or

with food consumed in the early part of a rehydration period.

Using the meta-analysis presented in this paper, full recovery of

the fluid deficit within 6 hrs requires ingestion of a rehydration

solution containing 100 mmol/L sodium if consuming the same

volume of fluid that was lost in the prior dehydration. Alter-

natively, correction of the fluid deficit can also be achieved by

ingesting 150% of the volume lost if the rehydration solution

contains 50 mmol/L sodium.

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Received January 9, 2006.



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