There are some genetic influrences that make a difference. Some people have a variation of the gene MTHFR that keeps them from changing the folate in food or the folic acid in supplements into the methylfolate the body actually uses. If they consume large amounts of folic acid supplements or even folate foods, their bodies actually get LESS useful methylfolate. They need to avoid ordinary B vitamin supplements and take a different but inexpensive form of the vitamin called methylfolate.A Also about 1% of the population of the US and UK, including me, has a genetic condition that causes our bodies to take too much iron out of our food. By the time you're 60 or so, you can literally begin to "rust." Some of us need less iron, not more.