I had a minor heart attack ten years ago, so I see a cardiologist every six months for a checkup. My cardiologist is a cyclist too and a real good guy, so we usually take a few minutes to talk about new routes and other riding stuff. I was complaining about the heat to him and how after one ride I felt slightly lightheaded and suspected low blood pressure. He asked me how much fluid I drank on the ride; I told him a full bottle – about 24 oz. for a 1 ½ hour ride. He said the lightheadedness was probably dehydration and advised me to drink a full liter of fluid for each hour that I rode.
He also reminded me that as you get older your sense of thirst changes a lot. A senior typically won’t feel thirsty until he is already dehydrated. That’s the case with me, I almost never feel thirsty. But it’s terribly important to keep drinking even if you don’t feel you need it.
It’s so basic, we always carry a full drink bottle on every ride, but we may not be drinking enough. I simply can’t drink a full liter per hour; if I try my stomach gets upset, but since my talk I do make sure I do intake a full bottle per hour, not per ride. Check it out, are you hydrating enough? In the summer it’s critical.