tag:theconversation.com,2011:/africa/topics/cold-drinks-29639/articlescold drinks – The Conversation2018-01-24T02:07:03Ztag:theconversation.com,2011:article/871802018-01-24T02:07:03Z2018-01-24T02:07:03ZWhat is kombucha and how do the health claims stack up?<figure><img src="https://images.theconversation.com/files/202023/original/file-20180116-53289-1snivqz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Kombucha is made from either a green or black tea base, with some interesting additions.</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/RiLzlQzwzik">Matt Hoffman</a></span></figcaption></figure><p>The drink kombucha was previously only popular in hipster cafes, but is now vying for space on the supermarket shelves. Many claims are made about the health benefits of drinking kombucha, but what does the science say?</p>
<p>For those of you who haven’t tried it, kombucha is a quirky-tasting drink. Depending on what’s added to it, it’s best described as a sour apple cider, perhaps with vinegary notes. </p>
<p>Kombucha is an ancient beverage that was <a href="http://onlinelibrary.wiley.com/doi/10.1111/1541-4337.12073/full">originally consumed</a> in China more than 2,200 years ago for its detoxifying and energising properties. As trade routes expanded, kombucha <a href="http://onlinelibrary.wiley.com/doi/10.1111/1541-4337.12073/full">found its way to Russia</a> and then into other eastern European areas. </p>
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<p><em><strong>Further reading: <a href="https://theconversation.com/is-apple-cider-vinegar-really-a-wonder-food-86551">Is apple cider vinegar really a wonder food?</a></strong></em></p>
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<p>During the second world war, kombucha was introduced into Germany, and in the 1950s it became popular in France and North Africa. By the 1960s, Swiss scientists claimed that kombucha was beneficial for the gut in a similar way to yoghurt.</p>
<h2>How it’s made</h2>
<p>Kombucha is made from either a green or black tea base. Added to that is white sugar, which has been fermented with a type of “tea fungus” called a <a href="https://en.wikipedia.org/wiki/SCOBY">symbiotic culture of acetic acid (vinegar) bacteria and yeast</a>, or SCOBY, for one to two weeks. </p>
<p><a href="https://link.springer.com/referenceworkentry/10.1007%2F978-3-319-19456-1_12-1">Detailed scientific recipes</a> are available for how to prepare kombucha. The taste of the kombucha changes during fermentation from a pleasantly fruity sour-like sparkling flavour, to a mild vinegary taste after a long incubation period. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/202025/original/file-20180116-53310-14pav93.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/202025/original/file-20180116-53310-14pav93.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/202025/original/file-20180116-53310-14pav93.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/202025/original/file-20180116-53310-14pav93.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/202025/original/file-20180116-53310-14pav93.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/202025/original/file-20180116-53310-14pav93.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/202025/original/file-20180116-53310-14pav93.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The SCOBY is a type of ‘tea fungus’.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/sterlingcollege/16240014580/in/photolist-qK5jxo-dQBHYV-mR95rj-dQBTyk-ni1dLa-h5GXij-9D98Cw-8MYwFg-fDEDut-bjJB13-Uf8ESA-e8vts9-71c3Kz-4qJbiB-cgyFpW-Uf91C7-bBTg4M-q5Cgzy-qKbhiR-8XBSX7-bAPaJp-6Fnj4k-nCgiu4-hbn5DU-6FniGP-9WPTRp-SezqmS-6Frq1N-95STFg-oGEv7k-edoCqL-6F94GM-4LKBLA-o2J4DU-4JyiU3-ebg89p-6Fnjbc-6FniP8-UACWYa-SKMR2q-2Xb9fg-aH2AHk-qsenNx-gPQXDa-ect1p4-UzQXam-e1T6sz-5ihauM-G3Twx-bZm2wJ">Sterling College</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>The <a href="https://theconversation.com/kitchen-science-bacteria-and-fungi-are-your-foody-friends-57279">fermentation</a> process is important, as the SCOBY changes the <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2835915/">polyphenols</a> – compounds normally found in tea, fruits and vegetables – into other organic compounds. This increases the acidity, which prevents other micro-organisms growing. </p>
<p>It is these new organic compounds that are claimed to provide health benefits beyond those <a href="https://theconversation.com/what-science-says-about-getting-the-most-out-of-your-tea-75767">already found in green or black tea</a>. </p>
<h2>The fermentation process</h2>
<p>The fermentation process extends the shelf-life of kombucha, as it does with other historically popular foods and drinks such as cheese, yoghurt, sauerkraut, kimchi, wine and beer.</p>
<p>Beer and wine become alcoholic during the fermentation process, whereas kombucha generally contains less than 0.5% alcohol. <a href="http://www.foodstandards.gov.au/code/userguide/pages/labellingofalcoholic4967.aspx">Food Standards Australian and New Zealand</a> classifies foods and drinks below 0.5% as non-alcoholic. </p>
<p>Ethanol, the alcohol you can drink, is produced when the yeasts and bacteria in the SCOBY interact via a process called <a href="http://www.icr.org/article/glycolysis-alcoholic-fermentation/">glycolysis</a>. The acetic acid bacteria in the SCOBY make use of the ethanol to produce vinegar (acetic acid), which contributes to its sour taste. </p>
<h2>Gut health</h2>
<p>Lightly fermented foods, made from bacteria, contain healthy bacteria. The theory is that these bacteria help colonise our gut, which <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4648921/">early research suggests</a> may improve a range of bodily functions from our mood and stress levels, to our weight and cravings for food.</p>
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<p>But simply ingesting healthy bacteria won’t necessarily cause these bacteria to permanently live in, or colonise, the gut. To gain any long-term health benefits from foods containing live bacteria, known as probiotics, the <a href="https://theconversation.com/poo-transplants-and-probiotics-does-anything-work-to-improve-the-health-of-our-gut-65480">current research suggests</a> you would need to take them continuously.</p>
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<p><em><strong>Further reading – <a href="https://theconversation.com/poo-transplants-and-probiotics-does-anything-work-to-improve-the-health-of-our-gut-65480">Poo transplants and probiotics – does anything work to improve the health of our gut?</a></strong></em></p>
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<p>There is some evidence that probiotics can be useful in some groups of people, such as those who suffer from certain gut problems like <a href="https://theconversation.com/poo-transplants-and-probiotics-does-anything-work-to-improve-the-health-of-our-gut-65480"><em>C. difficile</em> infection</a>. But the effect on other diseases like <a href="https://theconversation.com/explainer-what-is-inflammatory-bowel-disease-15173">inflammatory bowel disease</a> is uncertain. </p>
<p>The jury is still out on whether probiotics are beneficial to the wider population. So kombucha – or yoghurt, for that matter – won’t necessarily improve the health of your gut. To maintain good gut health, the best thing you can do is eat a wide variety of <a href="https://www.eatforhealth.gov.au/guidelines/australian-guide-healthy-eating">healthy foods</a>. </p>
<h2>Testing the other health claims</h2>
<p>A quick Google search will produce many exciting health claims about kombucha. These include detoxifying the blood, reducing cholesterol levels, reducing blood pressure, protecting against diabetes, antibacterial effects, and counteracting ageing. </p>
<p>When scientists want to evaluate the effect of a nutrient on health, we like to see that the studies have been done in humans, rather than animals. Many “lab bench” studies may begin by looking at isolated cells and then animals. This provides us with limited evidence, as human biological systems typically work differently. </p>
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<img alt="" src="https://images.theconversation.com/files/202024/original/file-20180116-53307-nlbuwd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/202024/original/file-20180116-53307-nlbuwd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/202024/original/file-20180116-53307-nlbuwd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/202024/original/file-20180116-53307-nlbuwd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/202024/original/file-20180116-53307-nlbuwd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/202024/original/file-20180116-53307-nlbuwd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/202024/original/file-20180116-53307-nlbuwd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">No human studies have tested the health claims of kombucha.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/roberrific/9108590564/in/photolist-eSTUCU-dQHs6m-aqWiUp-dQBQAM-q5CfyW-7Cw2WP-dQBWuZ-dQBQNn-qK5guE-UzQZgf-A1MZiG-dQBRBF-qK5jxo-dQBHYV-mR95rj-dQBTyk-ni1dLa-h5GXij-9D98Cw-8MYwFg-fDEDut-bjJB13-Uf8ESA-e8vts9-71c3Kz-4qJbiB-cgyFpW-Uf91C7-bBTg4M-q5Cgzy-qKbhiR-8XBSX7-bAPaJp-6Fnj4k-nCgiu4-hbn5DU-6FniGP-9WPTRp-SezqmS-6Frq1N-95STFg-oGEv7k-edoCqL-6F94GM-4LKBLA-o2J4DU-4JyiU3-ebg89p-6Fnjbc-6FniP8">Rob Campbell</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
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<p>For kombucha, there is only evidence from lab bench studies and animal studies. No published studies come from human clinical trials of drinking kombucha. </p>
<p>Two reviews of the lab bench and animal studies on kombucha from <a href="http://onlinelibrary.wiley.com/doi/10.1111/1541-4337.12073/abstract">2014</a> and <a href="https://www.sciencedirect.com/science/article/pii/S0963996900000673">2000</a> suggest the drink may have antimicrobial, antioxidant, anti-cancer and anti-diabetic properties. </p>
<p>The reviews also note some exciting mechanisms by which kombucha could potentially be used to treat gastric ulcers and high cholesterol, and improve the body’s immune response and liver detoxification. But they do not yet tell us if they translate to humans.</p>
<p>A chemical called DSL (D-Saccharic acid-1,4-lactone) is potentially the most beneficial component in kombucha. DSL has the <a href="http://www.madikombucha.com/academic_information_detail.php?lg=en">potential to inhibit</a> an important enzyme, β-glucuronidase, which may be linked to cancer growth. But once again, this has not been shown in humans.</p>
<p>Lab-bench <a href="http://onlinelibrary.wiley.com/doi/10.1111/1541-4337.12073/epdf">studies</a> have, however, detected the presence of polyphenols, acids and vitamins that are also found in regular green and black tea. </p>
<h2>What’s the verdict?</h2>
<p>Based on the current evidence, we can say the health properties of kombucha are likely to be similar to drinking tea or other fermented foods. If you enjoy kombucha, continue drinking it, but if you favour the traditional black and green tea, there are good health reasons to continue drinking those.</p>
<p>While some exciting properties have been shown from lab bench and animal studies, it doesn’t necessarily follow that we will see these benefits in humans. </p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/what-science-says-about-getting-the-most-out-of-your-tea-75767">What science says about getting the most out of your tea</a>
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</em>
</p>
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<p>Keep in mind that some of the kombuchas on the market have fruit juice added after the fermentation process, which will contribute to your overall <a href="https://theconversation.com/health-check-how-much-sugar-is-it-ok-to-eat-57345">sugar intake</a>. The amount of sugar in these varieties can range from 10-15g per serve (two to three teaspoons), so if you have regular tea without sugar, drinking kombucha will increase your sugar intake.</p><img src="https://counter.theconversation.com/content/87180/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>There are some interesting animal studies on kombucha but the jury is still out on whether it’s any healthier than tea.Evangeline Mantzioris, Lecturer in Nutrition, University of South AustraliaPermal Deo, Lecturer and Researcher, University of South AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/696212017-01-01T18:33:53Z2017-01-01T18:33:53ZHealth Check: does my brain really freeze when I eat ice cream?<figure><img src="https://images.theconversation.com/files/148830/original/image-20161206-25746-95rx47.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Little does this woman know what happens to her brain when she licks the ice cream.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/download/confirm/435069991?src=up5tXtzXv9_SlCpFnzUswg-3-17&id=435069991&size=medium_jpg">from www.shutterstock.com</a></span></figcaption></figure><p>It’s a long, hot summer’s day and you’re looking forward to an ice cream. But within seconds of your first bite, you feel a headache coming on: a brain freeze.
What’s going on?</p>
<p>Your brain isn’t literally freezing, or even sensing cold. It can’t sense cold or pain because it lacks its own internal sensory receptors. In fact, surgeons usually perform brain surgery on conscious, sedated patients with the only pain coming from the scalp, skull and underlying tissues, not from the brain itself.</p>
<p>An <a href="http://cep.sagepub.com/content/33/9/629.full">international team of neurologists</a> classifies brain freeze or ice cream headache as a:</p>
<blockquote>
<p>headache attributed to ingestion or inhalation of a cold stimulus. </p>
</blockquote>
<p>Anything cold (solid, liquid or gas) that passes over the roof of the mouth (the hard palate) and/or the back of the throat (posterior pharyngeal wall) can trigger a brain freeze headache.</p>
<p>Pain can be to the front of the head or the temples and while short lasting, can be intense, though not debilitating. People who have these headaches <a href="http://onlinelibrary.wiley.com/doi/10.1111/head.12688/abstract">usually do not seek treatment</a>, so there has been very little research into how brain freeze occurs.</p>
<p>The transient nature of these headaches means common “treatments”, <a href="http://www.wikihow.com/Stop-Brain-Freeze">like putting your tongue on the roof of your mouth</a>, are unlikely to have any major effect.</p>
<p>People most likely to have brain freeze also tend to suffer from migraines, suggesting a common underlying mechanism for both.</p>
<p><a href="http://cep.sagepub.com/content/24/4/293.abstract">One study</a> compared how common brain freeze was in people with migraine alongside those with tension type headaches. When an ice cube was placed on the hard palate of their mouths for 90 seconds, 74% of migraine sufferers reported pain along their temples versus 32% of those with a history of primary headache disorders (headaches that do not have an underlying or identifiable cause). </p>
<p><a href="http://cep.sagepub.com/content/early/2016/05/19/0333102416650704.abstract">Only 12%</a> of volunteers without a history of primary headache disorder experienced brain freeze headache with the same stimulus. These observations are robust and have been <a href="http://cep.sagepub.com/content/32/15/1123.abstract">replicated</a>.</p>
<h2>What causes brain freeze?</h2>
<p>An old fashioned idea about the cause of migraine suggested excessive blood flow through the blood vessels that supply blood to the brain caused the pain. However, this vascular hypothesis for migraine, <a href="https://en.wikipedia.org/wiki/Migraine">although still popular</a>, is now largely <a href="http://www.annualreviews.org/doi/abs/10.1146/annurev-physiol-030212-183717">discredited</a>.</p>
<p>Just like migraines, brain freeze headaches are accompanied by <a href="http://www.fasebj.org/content/26/1_Supplement/685.4.abstract">changes in blood flow</a> through <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2127417/">the arteries of the brain</a>. The link between pain associated with altered brain artery blood flow has <a href="http://www.wakehealth.edu/News-Releases/2013/Brrrrrrrrr!_It_s_Brain_Freeze_Season.htm">led some to speculate</a> the blood flow changes may actually <a href="http://cep.sagepub.com/content/early/2016/05/19/0333102416650704.abstract">cause the pain</a>. But an association between blood flow and pain doesn’t necessarily mean one causes the other.</p>
<p><a href="http://www.nature.com/scientificamerican/journal/v299/n2/full/scientificamerican0808-56.html">Another theory</a> about what causes migraine relates to altered excitability of neuronal pathways that detect and transmit the sensation and pain in the head via the <a href="http://emedicine.medscape.com/article/1873373-overview">trigeminal system</a>, the major nerve that transmits sensory information from the head to the central nervous system.</p>
<p>Ordinarily the cold sensation is not painful. However, if the trigeminal system is prone to over-excitability in people with migraine, pain kicks in at lower level (a lower threshold). If an over-excitable trigeminal system also applies to people with brain freeze, then the threshold may be low enough to activate pain after only a brief exposure to ice cream.</p>
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<a href="https://images.theconversation.com/files/150029/original/image-20161214-18882-uz447v.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/150029/original/image-20161214-18882-uz447v.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/150029/original/image-20161214-18882-uz447v.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1171&fit=crop&dpr=1 600w, https://images.theconversation.com/files/150029/original/image-20161214-18882-uz447v.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1171&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/150029/original/image-20161214-18882-uz447v.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1171&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/150029/original/image-20161214-18882-uz447v.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/150029/original/image-20161214-18882-uz447v.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/150029/original/image-20161214-18882-uz447v.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="attribution"><span class="source">Zenobia Ahmed / The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>Researchers are studying what causes hyper-excitability of the trigeminal system. The effects of a specific chemical signalling molecule CGRP (calcitonin gene-related peptide) released by trigeminal neurons are a <a href="http://www.nature.com/scientificamerican/journal/v299/n2/full/scientificamerican0808-56.html">necessary component of migraine pain</a>.</p>
<p>In genetically inherited migraine, the cellular processes that result in the release of CGRP from trigeminal neurons <a href="http://www.annualreviews.org/doi/abs/10.1146/annurev-physiol-030212-183717">has been altered</a>. These same mechanisms may explain the hypersensitivity to cold stimulus in ice cream headaches.</p>
<p>It seems likely that all headaches are the result of changes in activity in the trigeminal system, although why we perceive them in the front of the head and at the temples in particular is a mystery.</p>
<h2>Is there anything I can do to stop brain freeze?</h2>
<p>While we do not know exactly what causes brain freeze, there may be a simple way to reduce your chances of having one this summer.</p>
<p>Research shows how long brain freeze headaches last relates to the <a href="http://cep.sagepub.com/content/early/2016/05/19/0333102416650704.abstract">surface area</a> of the mouth that comes into contact with the cold stimulus. So, if you want to reduce your chance of a brain freeze, you may want to avoid gulping down your ice cream all at once. Take small nibbles instead.</p><img src="https://counter.theconversation.com/content/69621/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>It’s a long, hot summer’s day and you’re looking forward to an ice cream. But within seconds of your first bite, you feel a headache coming on: a brain freeze. What’s going on?Yossi Rathner, Lecturer in Human Physiology, Swinburne University of TechnologyMark Schier, Senior Lecturer in Physiology, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/628542016-07-26T12:24:33Z2016-07-26T12:24:33ZDoes drinking hot tea in summer really cool you down?<figure><img src="https://images.theconversation.com/files/131406/original/image-20160721-32610-1rlsu1f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Refreshing – or a sentence to sweat?</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/cat.mhtml?lang=en&language=en&ref_site=photo&search_source=search_form&version=llv1&anyorall=all&safesearch=1&use_local_boost=1&autocomplete_id=&searchterm=tea%20summer&show_color_wheel=1&orient=&commercial_ok=&media_type=images&search_cat=&searchtermx=&photographer_name=&people_gender=&people_age=&people_ethnicity=&people_number=&color=&page=1&inline=247474183">Shutterstock</a></span></figcaption></figure><p>I remember as a child, on the rare warm days that we used to get in Britain, my grandmother telling me to “have a cup of black tea … it will help cool you down”. As a seven-year-old, this seemed like a crazy idea, especially when all I wanted was a cold lemonade and another ice cream. But it appears that this old wives’ tale may actually be more Stephen Hawking than Stephen King.</p>
<p>The idea of drinking hot drinks in warm weather goes back hundreds of years. <a href="http://www.bbc.co.uk/news/magazine-27991440">Tea, or “chai” is one of the most popular drinks in India</a>, and many of the <a href="https://en.wikipedia.org/wiki/List_of_countries_by_tea_consumption_per_capita">leading consumers of tea per capita are in tropical or desert regions</a>. Recently, evidence has begun to emerge that drinking hot drinks may really help to <a href="http://www.ncbi.nlm.nih.gov/pubmed/22574769">cool you down</a>, too.</p>
<p>In 2012, <a href="http://sydney.edu.au/health-sciences/about/people/profiles/ollie.jay.php">Ollie Jay</a> published the <a href="http://www.ncbi.nlm.nih.gov/pubmed/22574769">first of a series</a> of papers to see if drinking a warm drink can actually lower the amount of heat stored by the body compared to a cold drink. In this first study, volunteers were asked to cycle at a relatively low intensity for 75 minutes in around 24°C heat, 23% relative humidity, while consuming water at either 1.5˚C, 10˚C, 37˚C or 50˚C. </p>
<p>The change in core temperature was slightly greater when 50˚C water was ingested compared to 1.5˚C and 10˚C water. However, when the authors considered the effect of drink temperature on body heat storage, which is a better indicator of total body temperature, the results were very different. Following the ingestion of the warm drink, overall body heat storage was actually lower following exercise than with cooler drinks. </p>
<h2>The sweat factor</h2>
<p>An explanation for these findings appears to be related to how sweating may be influenced by drink temperature. Sweating, and more importantly the evaporation of this sweat, is one of the <a href="https://theconversation.com/from-perspiration-to-world-domination-the-extraordinary-science-of-sweat-62753">key avenues for modulating body temperature and maintaining heat balance</a>. </p>
<p>Due to the increased heat load from drinking a warm drink, there is a compensatory increase in overall sweat output, which outweighs the internal heat gain from the warm drink. Consistently, a 50˚C drink results in a higher whole body sweat loss (around 570ml vs about 465ml for 1.5˚C). In practical terms, this means that more sweat is produced which is evaporated from the skin surface, increasing heat loss from evaporation and reducing body heat storage. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/131969/original/image-20160726-7041-1mx6fjd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Cold water: should he drink it?</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/cat.mhtml?lang=en&language=en&ref_site=photo&search_source=search_form&version=llv1&anyorall=all&safesearch=1&use_local_boost=1&autocomplete_id=&searchterm=runner%20hot&show_color_wheel=1&orient=&commercial_ok=&media_type=images&search_cat=&searchtermx=&photographer_name=&people_gender=&people_age=&people_ethnicity=&people_number=&color=&page=1&inline=154131425">Shutterstock</a></span>
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<p>Importantly, however, this study was conducted under conditions that allowed complete evaporation of sweat – in other words dripping sweat was limited by maintaining a good airflow and keeping humidity low. The results would likely be different in conditions where sweat evaporation is limited, such as in hot and humid conditions. In fact, drinking cold drinks may be more favourable in these circumstances, minimising inefficient sweat losses – dripping sweat – and consequently aiding an individual’s hydration status. </p>
<h2>Mouth or stomach?</h2>
<p><a href="http://www.ncbi.nlm.nih.gov/pubmed/24577060">In a second study</a>, Jay aimed to establish the effect of drink temperature on local sweat rate, and to determine the location of thermoreceptors that may influence sweating. They demonstrated that with differing drink temperatures, colder drinks (1.5˚C) resulted in reductions in local sweat rate compared to when warm drinks were ingested (50˚C), despite identical changes in core and skin temperature.</p>
<p>Interestingly, however, differences in the sweat response were found when fluid was either swilled around the mouth or delivered directly to the stomach via a nasogastric tube. The data showed that only when cold drinks were delivered directly to the stomach did they result in reduced local sweat rate. This data indicates that the sensors responsible for influencing the sweat response, and therefore regulation of body temperature, reside somewhere in the abdominal cavity. </p>
<p>In a <a href="http://www.ncbi.nlm.nih.gov/pubmed/?term=Ice+Slurry+Ingestion+Leads+to+a+Lower+Net+Heat+Loss+during+Exercise">third study conducted in their lab</a>, the team asked people to consume either 37˚C fluid or ice during exercise. In agreement with their previous work, they showed that there was a reduction in heat loss following ice ingestion compared to fluid at 37˚C, as a result of reduced sweat evaporation from the skin surface. </p>
<p>This has implications for endurance performance in the heat. In essence, where changes in body temperature are known to <a href="http://www.ncbi.nlm.nih.gov/pubmed/10066720">influence performance, ice ingestion</a> could result in an increase in body heat, negatively influencing endurance capability. The ingestion of an iced drink prior to exercise and in hot and humid environments, however, should be beneficial. </p>
<p>So, depending on your environmental conditions, maybe reaching for that cup of tea isn’t such a crazy idea after all. Plus the moral of the story: listen to your grandmother’s advice – it’s based on years of experience.</p><img src="https://counter.theconversation.com/content/62854/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Here’s the science.Steve Faulkner, Research associate, Loughborough UniversityKaty Griggs, Research Assistant and PhD student, Loughborough UniversityLicensed as Creative Commons – attribution, no derivatives.