I've heard that spicy food can increase circulation. I don't know if there is much truth to it or not.
I also read a book, "The Secrets of Warmth" I think it was called. I don't remember the author, but he wrote about how you can help increase circulation with cold and hot water baths. I don't remember the specifics, you should check that book out before running with that one. The book was mostly stuff that most anyone who spends a good deal of time in the cold knows, but it might be worth a quick skim. I found it at our public library.
The thing that has helped me the most is keeping a really close eye on my heat level and decreasing the amount of insulation to keep myself from sweating too much and getting my insulation damp. Keeping your core warm goes a long way to keeping the hands and feet warm. Not that I've ever been anywhere near as high as 6500m, except in an airplane.
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If women ruled the world there would be no wars, just be a bunch of jealous countries not talking to each other.