Water is virtually everywhere, from soil moisture and ice caps, to the cells inside our own bodies. Depending on factors like location, fat index, age, and sex, the average human is between 55-60% water. At birth, human babies are even wetter. Being 75% water, they are swimmingly similar to fish. But their water composition drops to 65% by their first birthday. So what role does water play in our bodies, and how much do we actually need to drink to stay healthy? The H20 in our bodies works to cushion and lubricate joints, regulate temperature, and to nourish the brain and spinal cord. Water isn't only in our blood. An adult's brain and heart are almost three quarters water. That's roughly equivalent to the amount of moisture in a banana. Lungs are more similar to an apple at 83%. And even seemingly dry human bones are 31% water. If we are essentially made of water, and surrounded by water, why do we still need to drink so much? Well, each day we lose two to three liters through our sweat, urine, and bowel movements, and even just from breathing. While these functions are essential to our survival, we need to compensate for the fluid loss. Maintaining a balanced water level is essential to avoid dehydration or over-hydration, both of which can have devastating effects on overall health. At first detection of low water levels, sensory receptors in the brain's hypothalamus signal the release of antidiuretic hormone. When it reached the kidneys, it creates aquaporins, special channels that enable blood to absorb and retain more water, leading to concentrated, dark urine. Increased dehydration can cause notable drops in energy, mood, skin moisture, and blood pressure, as well as signs of cognitive impairment. A dehydrated brain works harder to accomplish the same amount as a normal brain, and it even temporarily shrinks because of its lack of water. Over-hydration, or hyponatremia, is usually caused by overconsumption of water in a short amount of time. Athletes are often the victims of over-hydration because of complications in regulating water levels in extreme physical conditions. Whereas the dehydrated brain amps up the production of antidiuretic hormone, the over-hydrated brain slows, or even stops, releasing it into the blood. Sodium electrolytes in the body become diluted, causing cells to swell. In severe cases, the kidneys can't keep up with the resulting volumes of dilute urine. Water intoxication then occurs, possibly causing headache, vomiting, and, in rare instances, seizures or death. But that's a pretty extreme situation. On a normal, day-to-day basis, maintaining a well-hydrated system is easy to manage for those of us fortunate enough to have access to clean drinking water. For a long time, conventional wisdom said that we should drink eight glasses a day. That estimate has since been fine-tuned. Now, the consensus is that the amount of water we need to imbibe depends largely on our weight and environment. The recommended daily intake varies from between 2.5-3.7 liters of water for men, and about 2-2.7 liters for women, a range that is pushed up or down if we are healthy, active, old, or overheating. While water is the healthiest hydrator, other beverages, even those with caffeine like coffee or tea, replenish fluids as well. And water within food makes up about a fifth of our daily H20 intake. Fruits and vegetables like strawberries, cucumbers, and even broccoli are over 90% water, and can supplement liquid intake while providing valuable nutrients and fiber. Drinking well might also have various long-term benefits. Studies have shown that optimal hydration can lower the chance of stroke, help manage diabetes, and potentially reduce the risk of certain types of cancer. No matter what, getting the right amount of liquid makes a world of difference in how you'll feel, think, and function day to day.
水幾乎無所不在 從土壤水分及冰帽 到人體內的細胞 依據一些因素,例如所在位置 脂肪指數 年齡 及性別而不同 一般人體內約有 55 - 60% 是水分 剛出生的嬰兒甚至更多 水分佔了全身的 75% 非常類似魚的水含量 然而在周歲前 體內的水分會降至 65% 那麼,水在我們體內 扮演什麼角色呢? 我們該喝多少水維持健康呢? 水在人體內負責緩衝及潤滑關節 調節體溫 滋養大腦及脊髓 水不只是存在於血液中 成人的腦及心臟幾乎 3/4 是水 大約等同於 1 根香蕉的含水量 肺比較類似蘋果,有 83% 的水 甚至看起來乾燥的骨頭都含有 31% 的水 若我們主要是由水構成 並且生活周遭都有水 為何我們還需要喝那麼多水? 我們每天流失 2 至 3 公升的水 藉由排汗 大小便 甚至呼吸而流失 然而這些功能對我們生存又很重要 所以我們需要彌補流失的體液 維持體內水分平衡是必要的, 以避免脫水 或體內水分過多 兩者皆會對整體健康 造成嚴重的影響 體內開始偵測到水分過低時 腦部下視丘的感應接收器 就會發出訊號, 通知釋放 抗利尿激素/ADH 當 ADH 抵達腎臟時 會造成 水孔蛋白/aquaporins 一種特殊的通道 使血液吸收並保留更多水分 造成濃縮及深褐色的尿液 脫水加重會造成明顯的精力減退 心情不振 皮膚變乾 低血壓 以及認知障礙的症狀 脫水的腦會比正常的腦 更難完成同等份量的工作 甚至會因為缺水而暫時萎縮 體內水分過多,也就是低鈉血症 通常是因為短時間內攝取過多水分 運動員是較常見 體內過多水分的受害者 因為在極端的身體狀況下, 難以調節水分所導致 腦部脫水會使 ADH 分泌增加 反之,過多水分的腦會使 ADH 釋放到血液變慢,甚至停止 體內的電解質鈉被稀釋 造成細胞水腫 嚴重的情況下 腎臟會無法負荷 大量被稀釋的尿液 水中毒隨之而發生 可能導致頭痛、 嘔吐 少數嚴重者甚至會痙攣或死亡 但那是一種非常極端的狀況 在一般日常生活中 保持體內水平衡非常容易 ─ 對我們這些相當幸運 可以取得乾淨飲水的人而言 長久以來 一般觀念都認為我們每天要喝 8 杯水 但這個數據已被重新調整過 現在的共識是 我們需要攝取的水量 主要取決於我們的體重及環境 建議男性每日水分攝取量 在 2.5 - 3.7 公升之間 女性則在 2 - 2.7 公升之間 範圍可彈性調整, 依照我們是否健康、 運動、 年老 或是否過熱 雖然水是最健康的飲品 但其他飲料 甚至含有咖啡因的咖啡及茶 也都可以補充體液 食物所含的水 約可補充我們每日水分攝取量的 1/5 水果及蔬菜 ─ 像是草莓 小黃瓜 甚至是花椰菜 皆含有超過 90% 的水分 在提供有用的營養及纖維同時 也能補充液體的攝取 良好的飲水習慣 也會帶來許多長遠的效益 研究顯示理想的水分攝取 可以降低中風的機率 協助控制糖尿病 也可能降低某些癌症的風險 不管如何,攝取適當的液體量 你身體的感受、 思考及日常作業 將會有很大的改善