Probably your diet, could be a sign you're starting to move into a diabetic phase.

Dutchmann, I just noticed this same thing myself this afternoon when I took my blood sugar except my blood has always seemed thick and dark and today it was lighter and much thinner. Watery is how I would describe it. I am curious as to why this happened. What I've done differently in the last few days is eat a lot less (couldn't help it and am back to eating better now) and have had a lot more water to drink. I can't find any research that connects to it, but everything I read seems to say thinner blood is better.

on days whn you notice it to be thin, how much water do you drink? or how much tea(caffeine) coffee do you drink as this dehydrates us. As a rule for every amount of these we drink we should be drinking the same in water to replace what the caffeine takes out of us. there are ways of controling our diabetic state or even reversing it as i have through nutrition. Look up vital functions of salt in the body, this will probably amaze you. I'd be interested to hear your quantities of water consumption & whether it might be related to your blood viscosity. Also acidity in our bodies is directly related to bad health. If i can be of any help to any one to show you where you can learn more please do not hesitate! I'm here to help!