I wasn't going to reply but you mentioned some very controversial subjects. My grams has osteoporosis and about half the docs all said caffeine is bad for it. The other half said BS. That topic hasn't been answered properly because the tests have been inconclusive. There are so many things that can contribute or take away from osteoporosis that they really haven't been able to isolate just one thing that causes it or makes it worse. They all seem to say the same thing however. Add more calcium to your diet.
Menopausal triggers include caffeine but also contains dozens of other triggers heat, alcohol, spicy food, and stress to name a few.
As for a specific number I haven't seen anyone say 400mg. Most of the stuff out there talks about moderation. One or two cups a day. I think the reason why 600mg's get picked is because it is considered to be on the side of a heavy drinker. Someone who drinks upwards of 5 - 7 cups a day. I have friends who polish off a 6 pack of Dew before the head to work. Each bottle has about 55mg of caffeine. Most of them wouldn't consider themselves a heavy caffeine drinker.