Magnesium deficiency and physical performance

Transcription

1 /. ',,. r' g11,1915 Magnesum defcency and physcal performance G. Stendg-Lndberg NTRODUCTON Three lnes of research orgnatng n the 197s amed to defne frst, the effect of strenuous effort on serum concentraton (Mg); second, the effect of the Mg defcency caused by strenuous exerton on the ntermedary metabolsm; and thrd, the effect of extracellular and ntracellular Mg concentraton on the ndces of physcal performance. The results of these studes undertaken by the author and her collaborators, as well as by other colleagues, wll be summarzed. T FFCT OF STRNUOUS FFORT ON SRUM Mg2+ Begnnng n 197, several authors reported a sgnfcant lowerng of Mg mmedately followng marathon runs, compettve skng and treadmll exercse n a clmatc chamber2-7. Snce no statstcally sgnfcant lowerng of Mg was found on re-examnaton at 24 h the termnaton of the strenuous effort, the fall n Mg was thought to b,transent. Contrary to these reports, no mmedate sgnfcant decrease n S-Mg was found ether on termnaton of moderately severe effort, Le. 4-km forced march, or a more severe effort, Le. two 7-km forced marches carred out by two separate groups of young, traned srael males at two.dfferent tmes (Fgure 1). Ths dscrepancy between our fndngs and those of other colleagues led 183.!! ;,! t \ M 1\-t-+ltJUMTN/)PWS1tAL ACTVTY,1'-1(.)5.1 r./.,./.:

2 ..,c,,...,., '..,. '......,.,.C,.M'.=''. '...' '..,..C.,,'='!.,. -.Magnesum and pbyscal actvty 1:1. 1 Ẹ.... cc... z... wooor () z!o : BFOR AFTR Fgure 1 S-Mg concentraton before and mmedately a 7-km forced march. ntal mean before,.83:1:.1 and,.764:1:.6, n= 15,p.5! > us to undertake a seres of systematc studes on the effects of strenuous effort on S-Mg and relevant bochemcal and physologcal parameters. The age, weght and mean maxmal aerobc capacty CVO2ma) of the probands are gven n Table 1. n the frst of these studes, a sgpfcant fall n S-Mg was found mmedately followng a bout of extremely strel1ous exerton,.e. a l2o-km forced march of 22-h duraton (expermental condtons: ambent temperature 2-26 C, humdty 5-6%, estmated food Mg ntake 34mg, water Mg ntake 13 contanng 28 mg/l,.e. 367 mg, gvng a total Mg ntake of 77 mg)8. Ths was followed by an nsgnfcant ncrease 24 h and a second sgnfcant decrease 72 h, when 89% of theprobands were hypomagnesemc. A sgnfcant lowerng of S-Mg perssted on re-examnaton.,' r r,..,.j

3 'd,., \.-... CXJ V Table 1 Characterstcs of probands Age mean::sd (n) Study ::.5 (2) Study :: 1.4 (2) Study :: 1.3 (16) Study ::.5 (15) Observaton tme Wegbt VO 2max Type of te17nnaton Year of (kg) (ml kg- mn-) effort of strenuous effort publcaton 74.9:: :: km forced march 3 monrhs :: :: 4. 7-km forced march 18 days ?J:: :: km forced march 1 months :: :: km forced march 15 months 1991 J \J C'). Cl) :j ;::! ;:s C') Cl) :'u\ t 1 ;,;;,,,:.',,,_--=<,'-,=--,.,,,-,,..,--,-,---,--,-,,.:..:.:,:..' ,.:. :. '..., , '\ -.. -_n,- ':':1--- '---'-- t:: 1; - f: '-'.,.,-.,-,,.

4 ' o'.,, - J j,/:.magnesum and physcal actvty ss n = n;19 p = < n =2 NS n = 19 P-< n-18 <.5 C..:--' c: '- c: Q) c: U OJ :2:, UJ.7.6 before 12 KM march 1 hour 24 hours 72 hours 3 months Fgure 2 S-Mg concentraton before and up to 18 days a }O-km forced march 3 months later (Fgure 2). Ths study showed that the decrease of 5-Mg was not transent as suggested by other studes, but persstent. Followng a 7-km forced march of 13-h duraton (expermental condtons: ambent temperature C, humdty 57-75%, food Mg ntake 27mg, water Mg ntake 81 contanng 28mg/l,.e. 226mg, a total of 496 mg),no decrease n Mg was found the termnaton of the march, as observed prevously. However, a delayed, sgnfjcantclecrease n S-Mg was found 72 h (Fgure 3), when 95% of the probands were hypomagnesemc9. The lowerng of S-Mg (estmated n an atomc absorpton spectrophotometerjo) was sgnfcant, both n comparson wth thc baselne value, and wth the mean of an apparently healthy sracj populaton 11. Furthermore, the 5-Mg was stll sgnfcantly decreased on reexamnaton 18 days the termnaton of the forced march. Snce the lowerng of S-Mg was persstent, and a chronc lowerng of 5-Mg s accompaned by a decrease 11the ntracellular Mg contentj2, thc fndng sgnfed the presence of Mg defcency as a sequel of strenuous effort. Tlls novel and mportant observaton stmulated further research carred out on two groups of 16 and 15 solders of two elte. unts. Here the observaton tme was extended to 1 and 15 months, respectvely, aftcr the 186 ' İ!,

5 ,.. '.,t',,., '- Defcency and performance.,..9'.8 - c n = n 17 NS.763.:!:..114 n=19 NS ,46 n =2 n 2 p=<d.o1 p=<d.5.j---'- Ẹ c (.).7 th.6 Before 7 Km marro 1 hour attar 24 hours attar 72 hours aftar 18 days aar Fgure 3 march S-Mg concentraton before and up CO3 months a 12o..km forced completon of a 12-km forced march (whch was preceded by 6.5 months of tranng, and a 7-km forced march 2 weeks pror to the 12-km forced march). Followng the latter, the solders dd not undergo further bouts of strenuous effort although they dd carry out daly outdoor physcal actvty not exceedng an energy expendture of 4kcal/day (l6.7mj). n one group, the decrease of mean 5-Mg was stll apparent 6 months the march. After 1 months, whch was the end of the observaton tme, the mean stll remaned below the reference nterval ( mmol!l) (Fgure 4). n the second group, the sgnfcant decrease n the mean was stll apparent 11 months the 12-km march (Fgure 5). These studes gave further proof of the fact that strenuous effort gves rse to a chronc lowerng of 5-Mg, Le. to Mg defcency of strenuous effort!. T FFCT <?F Mg DFCNCY OF STRNUOUS XRTON ON T NTRMDARY MTABOlSM Mg2+ s essental for ntermedary metabolsm!3-!7.. n the.glycolytc pathway, seven out of ts 13 steps are Mg2+-dependent and n the trcarboxylc acd cycle (Krebs' cycle) three out of the nne steps are Mg :. 1, : {, :!.,. '. l.,! :1!! : :! :1 ',! l. ;

6 ;r' A r:. lvlagnesum and pbyscal actvty.- J.,.' --'. '... - '- c: 1. n=2.9 P<O.OO c:: Q.) u c:: u ') L./) A n=13 P<O.O 1 n=12 B c' Fgure 4 S-Mg concentraton at 6 months CB) and 1 months Cc) a 12-km forced march, compared wth the baselne value of 2 probands CA):p =probablty value dependent, e.g. the ntal converson of pyruvate to acetyl-coenzyme A through the actvaton of pyruvate dehydrogenase13-17 by Mg2+. Consequently, the metabolc changes followng strenuous exerton over tme were examned, along wth the montorng of S-Mg. The most strkng result of these studes was the fndng of a delayed rse n serum trglycerdes, blood sugar and serum cholesterol. n the 7-km long forced march9, the serum trglycerdes began to rse 24 h termnaton of the effort and were stll sgnfcantly rased on the 18th day (Fgure 6). The blood sugar began to decrease begnnng 24 h, and at 72 h began to rse steadly, becomng sgnfcantly rased 18 days (Fgure 7). Serum cholesterol, an ntal tendency to fall slghtly begnnng 1 h, reached a nadr at 72 h and peaked sgnfcantly 18 days (Fgure 8). n one of the studes followng a 12-m foced march), the mean serum trglycerdes were rased sgnfcantly 6 months termnaton of strenuous effort, and rose agan at 9 months to reach the upper border of the reference range 11 months (the end of the observaton tme) (Fgure 9). The blood sugar rose steadly untl 9 months when t reached a value sgnfcantly hgher than the baselne, and there, at 11 months t was found to be decreased, although not sgnfcantly (Fgure 1). Ths 188

7 '... - '!c:'.,;'.;;;;;', ;;',,,;,,' ','...,,,'....,C';',','',.'.! ':«.'.,.c':...;,'.;;,,; :;,...',.\'F';'\'h''!-;;u:;;;:;'.',.;,;;,,:, >,;:,,.;,;;..:,:;','3..,;;;;,..',,'j,.':, '',:-c.,,;,;;,,>; :(!.,J,;;>:';: J' Defcency and performance.-. J,,-, '- c:.8 1. n=2 N.S. N.S. n = 1 2 P <. 1 n = 1 n=14.,.,-' o::::r ' c: aj u c: w ) L V'>.6.4 A 8 c Fgure 5 S-Mgconcentraton at 9 CB),11 CC)and 15 CD)monrhs a 12-km forced march, com)ared wth the baselne value of 2 probands CA):p == probablty value; NS== non-sgnfcant., decrease was concomtant wth a second rse of serum trglycerdes. erum cholesterol, an ntal decrease whch lasted up to 9 months, began to rse and proved to be sgnfcantly rased at 11 months the 'termnaton of strenuous effort (Fgure 11). These studes showed for the.fust tme that the lowerng of serum trglycerdes, blood sugar and serum cholesterol, reported by many authors, dd, n the long run, gve way to ther delayed ncrease. Ths surprsng fndng suggests a potentally deleterous effect of strenuous effort on lpd profles n man. Ths, together wth the tendency to a delayed ncrease n blood sugar seen to follow exerton, could pose a health hazard to large sectons of the populaton engaged n strenuous effort...,, -!. 1 TU FFCT OF XTRA- AND NTRACLLUAR Mg2+ON Tl VOLUNTARY MUSCL CONTRACTON FORC AND OTlR NDCS OF PHYSCAL PRFORMANC t. n an earler study n Sweden of the bopsy samples of the quadrceps femors muscle n man, n chronc hypomagnesemal2, dramatc nrra- [, ' 189! L... L

8 /'::-.:. '--'.'-- '..... <>... 'N.A''-'-'-''M', 'A' -' r /.: - Magnesum and pbyscal actvty '..c ! LS (j) <D <D 1.1 U >. 1. > ::J....7 <D Cl) !:O.25 n;2.56;t j;.3 1.1;t.76 n;18 n;19 n;2 n;2 NS NS NS p=<.1.4 before 7 Km march 1h r alter 24 h 72h 18 days Fgure 6 Serum trglycerdes before and a 7-km forced march. The horzontal upper lne represenrs the upper border of the reference range, p values represent the probablty n comparson wth the baselne value, NS =nonsgnfcant cellular changes have been observed. These changes are characterzed by an ncrease n the ntracellular Na+, Ca2+, Cl-, cyclc AMp, and n ntersttal H2O, whle there s a decrease n Mg2+, K+, p3- and n the energy-rch phosphagens: ATp, ADp, and creatnne phosphate. A Mg2+-defcent cell was rghtly defned by Cronn and co-workers8, who found the same changes n dog muscle n expermentaly nduced Mg defcency, as a 'sck cell'. n the same studyl2, t was establshd that subjects wth chronc hypomagnesema have a sgnfcantly reduced mean maxmal voluntary muscle contracton force (MVC) of the quadrceps femors muscle, the bopsy of whch showed the above strkng electrolyte changes and the sgnfcant decrease n the phosphagen contents. Ths mportant fndng led to a further, enlarged study of 93 hypomagnesemc patents and 13 apparently healthy, normomagnesemc controlsl9. These 16 probands were screened for 6 varables usng a Rdge Regresson Statstcal Analyss. The varables conssted of! ;!,, \ t,.. t. t r \ [ 19.

9 - r--.. m '-,,,,-'-.,...,',... '--',,,',.,..,...,.-..,W,'..m,=.,,.,m,.., '-.h,,,'h'_'' (r: / /,.,', Defcency and performance l , : :t O :.62 n-2 n-18 n-19 n-2 n-2 N.S. N.S. p<.5 p<o.oo et 4.6 ::J en 4,4 't 4.2 m , j before 1 hour 24 hotn 7'2 hours 18 days 7 Kmmarch a:\er afar Fgure 7 Blood sugar before and a 7-km forced march. The horzontal lnes represent the reference range, p v:llues represent the probablty n comparson wth the baselne value, NS =non.sgntcant anthropometrc data, defnton of the degree of tranng of the probands, the MVC of the quadrceps femors muscle and 19 laboratory varables. The followng varables were found to be sgnfcantly assocated wth 'vfve: age, weght, heght, length of the tba, sex and four laboratory varables: serum Mg, serum Na+, blood-standard bcarbonate, and serum ron, and the dummy varables: moderate degree of tranng, and two dagnostc groups. \Vhen these explanatory varables were consdered together by means of the Rdge Regresson Analyss, only three factors proved to be statstcally sgnfcant: weght, age and S:Mg. These, then, were the determnants of the MVC, Le. of the physcal workng capacty. Ths result, together wth the e...xpermental data reported by other authors2-26, clearly ndcates that reducton of ntracellular Mg content (Le. the presence of Mg defcency) consttutes the prmary event, whch n (tro gves rse to the severe!!,! 191 \',,

10 -.-m,,',, '.,....'..,..'..'.'h','..,'. -,,',',C,H-'',...,',' ',,'_,r'.,.'j,,.',..';.'=',...c,.',..,,,.,, b,'c,,u Y',./.,'/ '/'. /! ; ;!,..,' ,. e.'.,! Magnesum and pbyscal ac!u(j' Cl Cl 4.6.r::. 4.4 (.) 4.2 (/j 4., n-2 n-18 n-19 n-2 n-2 p<.1 N..S. N.S. p<.1 b6fore 7 Km march T 1 hour attar 24 hrs. T 72 hrs afte r r 18 days aher...,,::'-... Fgure 8 Serum cholesterol before and a 7-km forced march. The horzontal lnes represent the reference range, p values represent the probablty n comparson wth the baselne value, NS =non-sgnfcant '.,..'! - ntracellular changes establshed by us, and consequently to the lowerng of MVC, whch leads to a lowered capacty for physcal performance. Another ndex of physcal workng capacty, the 1'O _max., was founel by - Lukask and co-workers27 to be sgnfcantly correlated to plasma Mg. Also, Conn and co-workers:!!:! reported that the l'o:!maxwas postvely assocated wth S-Mg n young male swmmers. The evdence whch shows that Mg defcency can result n a sgnfcant reducton of physcal performance has been revewed by Rayssguer and colleagues29 and McDonald and Keen3..',. ' Mg2+ SUPPLMNTATON AND PHYSCAL PRFORMANC As early as 1968, Ahlborg and co-workers31 tested the effect of Mg aspartate admnstraton on physcal performance n apparently. healthy Swedsh males. They found an ncrease of nearly 5% n the capacty for prolonged exercse n the treated probands compared wth placebo-treated cof1trol

11 h'.'.,.,,.. l1l r/t. / /. '-,; Defcency and performance 'j :!:.13 n= :!:.72 n=15 p<.1.98 :!:.29 n=15 p<o.oo 1.7=.75 n=15 p<.oo1 ::J 2.1.:::: (fj Q) - '- Q) >. 1.1 DJ.;:: -, (fj.6.1 before 12Km march af1er 6 months af1er 9 months 11 months Fgure 9 Serum trglycerdes before and a 12-km forced march. The upper horzontal lne represents the upper border of the reference range, p represents the probablry n comparson wth the baselne value, NS =non-sgnfcant, n 1972, Sen Gupta and Srvastava32 confrmed ths fndng, although they noted only a 23% ncrease n endurance32. Mg supplementaton of 4 weeks duraton was reported to ncrease physcal performance measured by means of VO.m-'C and by bcycle ergometry33. Rpar and co-workers36 found that Mg pdolate admnstraton n sub maxmal effort mproved cardorespratory performance. n 14 rowers gven Mg aspartate-hydrochlorde over 4 weeks, on ergometer testng, Golf and co-workers34 found no change n workng capacty. Smlarly, Rasmussen and co-workers35 faled to fnd any dfference n maxmum workng capacry n apparently healthy volunteers followng a 1 mmol nfuson of MgCz compared wth placebo-treated controls. The dscrepancy found between the quoted results appears to be due to the dfferent Mg vehcles used and the dfferent dosage and duraton of Mg admnstraton. t s mportant to emphasze that t may take a long perod of tme before Mg defcency s abolshed and a steady state acheved37. t s essental that a fnal assessment of the effect of Mg substtuton on physcal performance s made only a saturaton of Mg metabolsm has been acheved \.,.., 1,.' [ 1

12 - ;- /. /,'Y./ Magnesum and physcal actvty 4.43 :!: :!: :!: :!: n=15 n=15 n=15 n=15 NS p<.1 NS ,u ::::, 5.,., C'O 4.5 DJ ::J f), co before alter alter alter 12 Km 6 months 9 months 11 months march / Fgure 1 Blood sugar before and a 12-km forced march. The horzontal lnes represent the reference nterval, p represents the probablty n comparson wth the baselne value, NS =non-sgnfcant :t :t :t :t.68 n=15 n=15 n=15 n=15 NS NS p<.5, ut ' 5. e 4.5 Q) (/) Q)..c 4. f) before 12Km march L../' 6 months 9 months 11 months Fgure 11 Serum cholesterol before and a 12-km forced march. The horzontal lnes represent the referel,1ce nterval, p represents the probablty n comparson wth the baselne value, NS = non-sgnfcant ; '., 194

13 -. - = '... Defcency and performance PUBLJ;CRALT MPUCATONS OF THS FNDNGS,...,-'_u '. t s generally agreed that the \Vestern det does not supply an adequate amount of Mg, and ths favors the presence of a margnal or an overt Mg defcencyll. t s known that a total daly ntake of Mg n food and water of 496 to 77 mg durng strenuous effort was unable to offset the appearance of Mg defcency from strenuous effort1,8.9. The srael average daly Mg food ntake s 2-3 mgll, smlar to that n other ndustralzed countres, but lower than that of our probands. The majorty of researchers recommend much hgher daly requrements, e.g mg/kg/day38. Consequently, large sectons of the srael populaton who engage n strenuous effort wll be a rsk of developng Mg defcency. As we have shown, the Mg defcency from strenuous effort s accompaned, n the long run, by an ncrease n serwn trglycerdes, blood sugar and serum cholesterol, whch n turn poses a cardovascular rsk. Mg defcency n strenuous effort wll also cause a decrease n capacty for physcal performance. These two deleterous health aspects of Mg defcency are. gue to the sgnfcance ofmg for energy processes, and the ntermedary metabolsm. Addtonal hazards to health may be posed by Mg defcency due to the mportance of Mg for the bosynthess of protens and nuc1ec acds, for neurotransmsson, receptor bndng, cell dvson and the ntegrty of the cell membrane Therefore t s of great mportance to establsh the optmal dosage, duraton and vehc1e for Mg supplementaton n order to be able to treat and prevent the Mg defcency of strenuous effort, both at the ndvdual level and the natonal level, partcularly n the populaton at rsk..:, CONCLUSON The results presented ndcate that both at the ndvdual as well as the natonal level the capacty for physcal performance mght mprove n large segments of the populaton engaged n strenuous effort once the prevalent margnal or overt Mg defcency s adequately tre,d. ACKNODGMNTS The author wshes to thank the Journal of Basc and Clncal Physology and Pbarmacology for permsson to reprnt Fgures ' J

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