Is caffeine a friend or foe?
By Laura Williamson, American Heart Association 线上电子游戏飞禽走兽
咖啡因 jump-starts your day and puts a bounce in your step. It can help you focus, improve your mood and maybe even help you live longer.
But how much is too much?
咖啡因, 天然兴奋剂, can be found in a variety of foods, 比如咖啡豆, 茶叶, 可可豆, guarana berries and yerba maté leaves. 它也可以合成并添加到饮料中，如苏打水和能量饮料. 研究 shows that about 90% of U.S. adults consume some form of caffeine every day.
One of the most popular ways people consume it is through coffee. Because of that, most caffeine research centers around this drink, said Dr. 格雷格·马库斯, 加州大学心脏病学研究副主任兼医学教授, 旧金山.
“总的来说，文献表明，喝咖啡通常不会损害健康,他说. “但我非常不愿意建议任何人开始喝咖啡，如果他们没有这样做, or to increase consumption for any health benefit."
Studies have found caffeine can do both good and harm. 经常喝咖啡的人可能不太可能患上慢性疾病, such as cardiovascular disease, 糖尿病, Parkinson's disease and some cancers. 一些研究表明，他们不太可能死于心脏病和其他疾病.
根据 Food and Drug Administration, 每天摄入400毫克的咖啡因——相当于四到五杯咖啡——被认为对健康的成年人是安全的. An 8-ounce cup of green or black tea has 30-50 mg of caffeine. Energy drinks may contain 40-250 mg for every 8 ounces, and a 12-ounce can of caffeinated soda contains 30-40 mg.
适量的咖啡因——最多两杯8盎司的咖啡——可以让人不那么累，更清醒. Some studies suggest it can reduce appetite and lower the risk for depression. But high doses – 12 cups or more – can make people feel anxious, raise blood pressure and lead to heart palpitations and trouble sleeping. For people who consume caffeine regularly, stopping consumption abruptly can lead to symptoms of withdrawal, 比如头痛, fatigue and depressed mood.
Determining how much is too much can be tough. 对一个人来说适量的咖啡因可能对另一个人来说是高剂量的. 马库斯说，这是因为有些人代谢咖啡因的速度比其他人快. 人们的体重和服用的药物等因素也会起作用. 的 bottom line is, caffeine affects everyone differently.
"的 compound is complex, and we need to recognize that not only might there be benefits and harms, but this may vary from one person to another,马库斯说.
他和他的同事最近完成了为数不多的关于咖啡因摄入的随机研究之一, 他在去年的美国心脏协会科学会议上做了报告. 研究人员要求参与者在两周内连续不超过两天喝咖啡或不喝咖啡.
的 发现, 在完整的结果发表在同行评议的期刊上之前，哪些被认为是初步的, 表明人们在喝咖啡的日子比不喝咖啡的日子更活跃，睡眠也更少. 他们也有更多来自下心室的不规则心跳，但较少来自上心室的异常心跳.
马库斯说，这项研究的一个局限性是，人们开始和停止摄入咖啡因, 是什么让那些习惯了每天喝咖啡的人产生了夸张的反应. "的 effects of caffeine are attenuated when you drink it regularly,他说. "的 body adapts to that caffeine level. And more regular consumption of caffeine can speed up the metabolism."
与身体分解咖啡因较慢的人相比，代谢咖啡因较快的人睡眠问题较少, 他说.
In his cardiology practice, 马库斯告诉那些睡眠困难或心律不正常的病人，看看咖啡因可能在起什么作用. “我通常建议，对于睡眠困难或心悸的患者来说，尝试摄入咖啡因是合理的. Take some time off of caffeine to see if it makes a difference." But he does not give a blanket recommendation to avoid caffeine.
马库斯并没有区分人们从咖啡、热茶或冰茶中获得的咖啡因. “两者之间可能存在健康差异，但尚未进行研究，”他说.
He is less flexible about the consumption of energy drinks, which typically have a higher concentration of caffeine, 以及添加甜味剂或碳水化合物，没有证据表明它们对健康有任何好处. 研究 已经发现能量饮料会导致心脏异常的电活动和持续数小时的高血压.
"In general, I would caution against the use of energy drinks,马库斯说.
的re are other ways to stay alert.
“提高警觉性的最佳策略和总体上最健康的策略是长期的健康习惯," such as getting a good night's sleep and exercising regularly, Marcus说. 他建议那些难以保持清醒的人咨询医生，看看他们是否患有睡眠呼吸暂停或其他睡眠障碍.
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