A recent study published in the European Journal of Nutrition says that for healthy young men, drinking less water daily, resulting in mild dehydration in the body, can impair vascular function in ways that are comparable to the dangers of smoking. According to the authors, “Mild dehydration is generally not felt, but like smoking, it causes damage to endothelial function.” The authors note, “Decreased endothelial function already occurs when dehydration is less than 2 percent. Further dehydration is what makes people feel thirsty.” The study enrolled 10 healthy young men who had endothelial function measured by flow-mediated arterial diastole (FMD) with and without dehydration and found a 26.8 percent decrease in FMD and a significant reduction in brachial artery internal diameter with dehydration. Previous epidemiological studies have found that dehydration is associated with diabetes, chronic kidney disease, and cardiovascular disease. The likely mechanism is over-activation of the renin-angiotensin-aldosterone system (RAAS) when drinking less water. Elevated levels of aldosterone in the blood then increase arterial stiffness. One study found that the risk of chronic kidney disease was also reduced in people who drank 3.2 liters of water per day. A 2002 study found that for men who drank ≥5 glasses of water per day, the risk of fatal heart disease dropped by 54% and for women by 41%. While water is not good and tasteless, drinking beverages can be harmful. The study found that the risk of fatal heart disease increased by 147 percent for women and 46 percent for men if they drank more beverages. Why is drinking more dangerous for women? It is believed that women’s blood vessels are thin and have less blood volume, so the consequences of drinking the same amount of beverages will be more serious. In particular, the harm of sweet drinks should not be underestimated. A study by Professor Frank Hu of Harvard University found that people who drank 1-2 cups of beverages a day had a 26% increased risk of diabetes, a 35% increased risk of myocardial infarction or sudden death, and a 16% increased risk of stroke. In short, drinking more water is good for your health, and drinking more beverages damages your body.