Are there some health related things that you know are true (at least for you) but for which there is no scientific basis? This could be something that affects your health positively or negatively. Let me get this out of the way: we know that correlation does not equal causation (yada yada) but go ahead and tell us about it anyway.
For example, I know that I sleep worst on full moons. I don't have an almanac at my house and don't keep track of the phases of the moon, however, like clockwork, I will have really bad sleep the few days around and on the full moon. It has happened too many times for me to ignore.