The notes that sound good together have a basis in the harmonic series, the 1st and 3rd are octaves of the fundamental, 2x an 3x the frequency. the 2nd harmonic and 4th harmonic make up the other 2 notes in a major chord. Periodic sounds that are not pure sine waves (like vibrating strings) have harmonics. Our ears are attuned to hear these harmonics and this natural phenomenon is the basis of all pitch, melody and harmony in music.
One thing I have recently become aware of, after my doctor ordered a test, is checking for mutations in the MTHFR gene. It's an enzyme which deals with how we process folate into its active form and is important in many pathways
Supposedly the C677T mutation increases your risk for heart disease. There is also another one, A1298C that is very common but no consensus on how it may effect health. I also matters whether you you have one or two copies of the mutations.
Some recommend supplementing with methylated B vitamins to offset the any negative health effects, but I'm still soaking this in and am not sure what the consensus is it yet.