The average man lugs around about 44 liters of water\u2014nearly 100 pounds worth\u2014tucked away inside his cells and filling the gaps between them, or coursing through his blood vessels. The average woman, in contrast, carries only 31 liters. Even when you consider that women are generally smaller than men, the difference persists: men\u2019s weight is about 58 percent water, women\u2019s is 49 percent. That\u2019s mainly because men have more muscle, which holds more water than fat tissue.<\/p>\n
The hard question, and the one that a recent review in the Journal of Applied Physiology<\/em><\/a> grapples with, is whether this makes any difference to how men and women respond to exercise-induced dehydration. To skip ahead to the punchline, the answer is that we\u2019re not sure yet, because most of the dehydration research has taken place on men. But the authors\u2014Kate Wickham and Stephen Cheung of Brock University, Devin McCarthy of McMaster University, and Lawrence Spriet of the University of Guelph\u2014make the case that there\u2019s enough evidence that we can\u2019t simply assume that there are no differences. The research needs to be done.<\/p>\n To start, it\u2019s worth noting that not everyone agrees with the premise that dehydration is a serious problem for athletes or exercisers, regardless of their sex. In fact, one of the authors of the new review, Cheung, did an elegant study back in 2015<\/a> in which cyclists were rehydrated (or, in the control group, not) with an IV drip inserted in their arms, so that they didn\u2019t know whether they were dehydrated or not. Under those circumstances, Cheung found that even sweating out three percent of your starting weight doesn\u2019t hinder performance. It\u2019s certainly clear (in my reading of the research, at least) that letting yourself get severely dehydrated will eventually hurt performance. It\u2019s less clear, however, that you need to do anything beyond drinking when you\u2019re thirsty<\/a> to avoid those problems.<\/p>\n There isn\u2019t much research directly comparing the dehydration responses of men and women, so Wickham and her colleagues found pairs of studies that put groups of men or women through similar protocols in order to compare the results. One of the patterns they observed was that core temperature seemed to rise sooner in women than men. For example, in a 120-minute cycling bout, core temperature started rising after 30 minutes in women, at which point they\u2019d lost as little as 0.5 percent of their starting weight. In men, temperature didn\u2019t start rising until 60 minutes and 1.5 percent weight loss.<\/p>\n One possible explanation for this observation is that women, with less water in their body to start with, are more sensitive to small sweat losses. It\u2019s not straightforward, though, because you can compensate for sweat losses by shifting fluids from other parts of the body to keep your blood volume stable. Indeed, in the cycling studies, women sweated out a greater percentage of their body mass but their blood plasma volume decreased by a similar amount compared to men.<\/p>\n There are also differences in how men and women sweat. Women tend to have smaller, less sensitive sweat glands with a lower maximal output than men\u2019s glands. To compensate, they have more sweat glands overall\u2014which, interestingly, may be why studies have found that women have \u201ca more even whole-body distribution of sweat than males during exercise.\u201d Overall, women sweat less than men, which may explain why they have a faster initial rise in core temperature when they start exercising. And other factors can influence sweating response, including the levels of female sex hormones through the menstrual cycle, which may also affect core temperature, fluid retention, and other contributors to hydration status.<\/p>\n On that note, it\u2019s worth looking back at an article I wrote last year<\/a>, on a major meta-analysis<\/a> by researchers Kelly McNulty and Kirsty Elliott-Sale on the effects of the menstrual cycle on exercise performance. On that topic, too, there were a bunch of suggestive but inconclusive results hinting at possible hormone-dependent differences. The question is: what do you do with these hints? One school of thought is that it changes everything. As one performance specialist recently tweeted<\/a>, \u201cIf a trainer\/coach doesn\u2019t know the menstrual cycle of his female athletes, he\u2019s not coaching them effectively.\u201d But that\u2019s not where McNulty and Sale come down: both recently pushed<\/a> back<\/a> against that blanket approach, in favor of individually tailored advice. For some women, they pointed out, the menstrual cycle doesn\u2019t seem to make any difference to their performance, so why add an extra layer of stress and complexity to their training?<\/p>\n That\u2019s a note of caution I would apply equally to the question of sex-specific hydration guidance. Wickham and her colleagues conclude with a set of questions to be answered by future research, for example about whether women really do start warming up more quickly in response to exercise. Until those questions are answered, let\u2019s hope the Twittersphere doesn\u2019t start issuing guidance on how women should hydrate. And even once the research is done, bear in mind that the difference between the average man and the average woman is likely far more subtle than, say, the difference between me and Haile Gebrselassie, whose 3.6 L\/hr sweat rate<\/a> was one of the highest ever measured. I\u2019d say the best advice is still the simplest, no matter who you are: if you\u2019re thirsty, drink.<\/p>\n For more Sweat Science, join me on Twitter<\/a> and Facebook<\/a>, sign up for the email newsletter<\/a>, and check out my book Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance<\/a>.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":" The physiological differences between men and women affect how much fluid they store, how they sweat, and how quickly they heat up. Does that matter?<\/p>\n","protected":false},"author":23631,"featured_media":2533305,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"uuid":"2645d8a5a820b9e41b80fa881466baef","footnotes":""},"categories":[2553],"tags":[2616,2679,5939,2601],"byline":[914],"ad_cat":[],"legacy-category":[],"class_list":["post-2533211","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-training-performance","tag-endurance-training","tag-gender","tag-outside-run","tag-science","cluster-sweat-science","byline-alex-hutchinson"],"acf":[],"parsely":{"version":"1.1.0","meta":{"@context":"https:\/\/schema.org","@type":"NewsArticle","headline":"Why Women Might Need Different Hydration Advice","url":"https:\/\/www.outsideonline.com\/health\/training-performance\/women-hydration-research\/","mainEntityOfPage":{"@type":"WebPage","@id":"https:\/\/www.outsideonline.com\/health\/training-performance\/women-hydration-research\/"},"thumbnailUrl":"https:\/\/cdn.outsideonline.com\/wp-content\/uploads\/2021\/10\/dibaba-hydration-marathon_h.jpg","image":{"@type":"ImageObject","url":"https:\/\/cdn.outsideonline.com\/wp-content\/uploads\/2021\/10\/dibaba-hydration-marathon_h.jpg"},"articleSection":"Training & Performance","author":[{"@type":"Person","name":"mmirhashem"}],"creator":["mmirhashem"],"publisher":{"@type":"Organization","name":"ºÚÁϳԹÏÍø Online","logo":"https:\/\/www.outsideonline.com\/wp-content\/uploads\/2021\/07\/favicon-194x194-1.png"},"keywords":["endurance training","gender","outside run","science"],"dateCreated":"2021-10-11T11:00:47Z","datePublished":"2021-10-11T11:00:47Z","dateModified":"2022-01-25T01:46:35Z"},"rendered":"
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