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.
水存在于日常生活中的每个角落, 从土壤水分、冰层, 到人体细胞中的水分。 基于某些因素,如地理位置, 肥胖指数,年龄,和性别, 每个人体内平均含有 55 - 60% 的水。 刚出生的婴儿体内含水更多。 75% 的含水量让他们看起来 像在水里游的鱼。 但是他们的水含量 会在一岁生日前降至 65% 那么,水在我们身体中 扮演什么样的角色呢? 我们到底要喝多少水 才能保持健康呢? 水在人体中的作用 有缓冲和润滑关节, 调节温度, 滋养大脑和脊髓。 水不仅存在于我们的血液。 成人的大脑和心脏 几乎有 3/4 是水。 几乎相当于香蕉中的含水量。 肺的含水量和苹果接近,有38%, 即使看起来很干燥的人的骨头 也含有 31% 的水。 如果人类主要由水构成, 而且生活的环境中充满水, 那为什我们还需要喝这么多水? 每天人体要流失2-3升的水。 它们通过汗液、尿液、 肠道运动 甚至呼吸而流失。 虽然这些活动对于生存十分必要, 但我们也需要补充体液的流失。 维持水平衡十分重要。 它能避脱水或过度脱水, 这两样都能损害人的整体健康。 一旦发现水含量过低, 下丘脑的感受器 就会提示身体释放抗利尿激素。 当此激素到达肾脏, 会打开水通道 即一种特殊通道, 它能够使血液吸收和保留水分, 导致尿液浓缩,引起黑尿。 加重的脱水能引起 明显的乏力、情绪低落、 皮肤干燥 和血压降低 以及认知障碍。 脱水的大脑要更加费力地运行 才能完成正常大脑的工作, 而且脱水大脑甚至会萎缩。 这主要由缺水、过度脱水 或低钠血症引起 通常在短时间内 过度消耗水的情况下发生。 运动员通常是过度脱水的受害者, 因为一些并发症, 这些并发症由极端身体状况下 水含量改变引起。 当脱水的大脑 促进抗利尿激素生成时, 过度脱水的大脑会运行缓慢, 甚至停止运行 , 并且把此激素释放到血液中。 人体中的钠电解液被稀释, 造成细胞膨胀。 在严重的情况下, 肾脏无法负荷被稀释的尿液的体积。 水中毒由此产生, 还有可能造成头疼、呕吐, 少数情况下出现癫痫或死亡。 但这仅仅出现在非常极端的情况下。 在一般的日常生活中, 维持一个水平衡的身体系统 是比较容易办到的。 因为我们足够幸运, 可以获取干净的饮水。 长久以来,常识告诉我们 一天要喝八杯水。 这个标准已经被微调了。 现在被普遍认同的说法是 我们所需的饮水量 主要取决于体重和所处环境。 推荐的每日摄入量是 男性 2.5 - 3.7 升, 女性 2 - 2.7 升。 这个范围可以适当增减, 如果我们处于健康、充满活力、年老 或发烧的状况下。 虽然水是最健康的湿润剂, 其他的饮料 甚至是含咖啡因的咖啡和茶 也能够补充体液。 食物中的水分占 我们每日摄入水分总量的 1/5。 水果和蔬菜, 如草莓、黄瓜, 甚至花椰菜的含水量 都超过 90%, 它们能在提供宝贵营养和 膳食纤维的同时补充体液。 喝水也许还有许多长期的好处。 研究显示最佳的水平衡 能降低中风的风险, 帮助控制肥胖, 已经可能减少某些癌症的风险。 无论如何 摄入适量的液体十分重要, 它影响着你的感受、思维 以及日常活动。