To be fair, even within the national recommendations, there may be different levels suggested for different groups. There are usually separate numbers suggested for infants, children, teenagers, adult men & women, the elderly, and pregnant/nursing women. The numbers that get tossed around most often are for adult men, but the separate recommendations do exist. The goal of the recommendations is to cover the needs of more than 97% of the group. Your doctor should be able to tweak those recommendations for your individual needs, as required.