New York Times で北半球のマラソンシーズン開幕に備えて、マラソン中の給水に関する最近の研究が2つ紹介されていた。せっかくなので、その紹介。
New York Times “How Much to Drink During a Marathon” October 5, 2011 By GRETCHEN REYNOLDS
水分補給に対する考えの変遷
Many of us who ran a marathon in the 1990s were cautioned to “stay ahead” of our thirst, with the warning that by the time we felt thirsty, we would be clinically dehydrated.
低ナトリウム血症(hyponatremia)の増加
水分を積極にとるようになってから、マラソン大会でexercise-associated hyponatremia(EAH)が増えている
But in the past few years, several marathoners died as a result of drinking too much, a dangerous condition called hyponatremia, or water intoxication. Before then, hyponatremia, marked by low blood sodium levels, had been unheard of in marathon fields.
新しいガイドライン
Most experts have now begun advising marathon runners to drink less. (snip) Recent guidelines from the International Marathon Medical Directors Association explicitly say to drink only when you’re thirsty.
The lesson of his and other studies, Dr. Winger is quick to point out, is not that endurance athletes should avoid hydrating. “The lesson is that you should drink only when you need to, when you’re thirsty,” he says. “That is the best way to protect yourself against hyponatremia” and also against dehydration. “Thirst is a very reliable indicator” of your body’s actual hydration status, he says.
市民ランナーの知識は古いまま
“There is still a widespread misconception that you have to ‘stay ahead’ of your thirst,” said Dr. James Winger, a professor of family medicine and lead author of the study. “That idea is contrary to science, and it is dangerous.”
But as his study’s results indicate, it remains surprisingly pervasive.
——
次の2つの研究をベースに記事が展開されていた。
[1]Sara Brown, George Chiampas, Carrie Jaworski, and Dennis Passe. Lack of Awareness of Fluid Needs Among Participants at a Midwest Marathon. Sports Health: A Multidisciplinary Approach September/October 2011 vol. 3 no. 5 451-454.
http://sph.sagepub.com/content/3/5/451.abstract
Almost 65 percent responded that they were “not at all” concerned about keeping themselves properly hydrated during the upcoming race.
Notably, when asked specifically whether they worried about the possibility of developing hyponatremia, 63 percent said that they were not.
[2]Winger JM, Dugas JP, Dugas LR. Beliefs about hydration and physiology drive drinking behaviours in runners. Br J Sports Med. 2011 Jun;45(8):646-9. Epub 2010 Sep 28.
http://www.ncbi.nlm.nih.gov/pubmed/20876587
http://bjsm.bmj.com/content/early/2010/09/28/bjsm.2010.075275.abstract
almost half of runners may be drinking too much during their races.
Just half of the runners surveyed reported drinking only when they felt thirsty, the yardstick now recommended by most sports experts. The others drank according to a preset schedule of some kind, and almost 10 percent told the researchers that they drank “as much as possible.”
—
How much fluid should i drink during endurance events?
IMMDA’s revised fluid recommendations for runners & walkers
http://aimsworldrunning.org/guidelines_fluid_replacement.htm
記事内で紹介されていた、International Marathon Medical Directors Association(IMMDA) の新しいガイドライン
ページの真ん中辺りに、NYTの記事に関わる記述がある。
Try to drink to thirst.
This advice seems way too simple to be true; however, physiologically the new scientific evidence says that thirst will actually protect athletes from the hazards of both over and underdrinking by providing real time feedback on internal fluid balance. If you are not thirsty, try to refrain from drinking. Do not feel compelled to drink at every fluid station nor follow the cues of other runners: their fluid needs are probably very different from your own. If you are “over-thinking” and feel you cannot rely on this new way of thinking, experiment in your training with one of these other ways realizing each has it’s own cautions as well.
—
Related Studies
適当に検索して見つかった関連研究を幾つか紹介
[3]Christopher S.D. Almond et al. Hyponatremia among Runners in the Boston Marathon. N Engl J Med 2005; 352:1550-1556April 14, 2005
http://www.nejm.org/doi/full/10.1056/NEJMoa043901
” Beliefs about hydration and physiology drive drinking behaviours in runners”([2]) に近い内容
面白いのは次の3点
1. hyponatremia x weight gain
レース前後で体重を測定した結果(増えた人も減った人もいる)
Hyponatremia was strongly correlated with weight gain during the race.（Figure 1参照）
Excessive consumption of fluids, as evidenced by substantial weight gain while running, is the single most important factor associated with hyponatremia.
2. 水分摂取がうまく行っているかどうやってチェックするか?
Sporadically checking their weight could be a relatively easy way for runners to determine whether their current hydration strategy puts them at undue risk for the development of hyponatremia.
エイドステーションごとにヘルスメーターをおき、選手に強制的に体重測定を義務付けろとでも言わんばかりの、現場を完全に無視した素晴らしいアドバイス。
ただ、レース前にシューズを履いた状態で体重を計測し、計測ポイントで踏みつけるときに体重も測定できれば(選手を特定するのはかなりの技術的困難を伴うと思うが)、調理のしがいのある面白いデータになりそう。
3. スポーツドリンクの効果
スポーツドリンクには電解質がいろいろと入っているが
We could find no association between the composition of fluids consumed and hyponatremia. (snip) our findings suggest that the contribution of the type of fluid is small as compared with the volume of fluid ingested.
水分摂取のタイミングに関しては NYTimes と同様
Because runners vary considerably in size and in rates of perspiration, general recommendations regarding specific volumes of fluids and frequencies of intake are probably unsafe and have been superseded by recommendations favoring thirst or individual perspiration rates as a primary guide.
以下のスタディはポインターだけ
[4]Yoram Epstein and Yoav Cohen‐Sivan. Exercise‐associated hyponatraemia: facts and myths. Br J Sports Med. 2007 February; 41(2): 111.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2658918/
[5]Mitchell H. Rosner, and Justin Kirven. Exercise-Associated Hyponatremia. CJASN January 2007 vol. 2 no. 1 151-161
http://cjasn.asnjournals.org/content/2/1/151.full
[6]Beat Knechtle, Patrizia Knechtle and Thomas Rosemann. Low prevalence of exercise-associated hyponatremia in male 100 km ultra-marathon runners in Switzerland. EUROPEAN JOURNAL OF APPLIED PHYSIOLOGY Volume 111, Number 6, 1007-1016
DOI: 10.1007/s00421-010-1729-7
http://www.springerlink.com/content/hj34116461246152/
[7]B. Knechtle, A. Wirth, P. Knechtle, T. Rosemann and O. Senn. Do ultra-runners in a 24-h run really dehydrate? IRISH JOURNAL OF MEDICAL SCIENCE Volume 180, Number 1, 129-134,
DOI: 10.1007/s11845-010-0500-8
http://www.springerlink.com/content/y50q28h132454027/
[8]Knechtle, Beat MD et al. Prevalence of Exercise-Associated Hyponatremia in Male Ultraendurance Athletes. Clinical Journal of Sport Medicine:May 2011 – Volume 21 – Issue 3 – pp 226-232
DOI: 10.1097/JSM.0b013e31820cb021
http://journals.lww.com/cjsportsmed/pages/articleviewer.aspx?year=2011&issue=05000&article=00009&type=abstract
Armchair Athlete's Miscellany 