Men just find it freaky that something can bleed for five days and not die. I think they're secretly afraid that we're harder than they are.
In all seriousness, it's likely to be down to hormones - birth control can do this as others have said, though personally I've never used the Pill and haven't ever experienced spotting either. IUDs can also cause bleeding.
Once you get past 40 periods can get very weird anyway, though you've not stated your age. So long as it's just spotting and not a significant amount of blood I doubt it will make you anaemic, though it probably won't hurt to include some iron rich foods in your diet.