I can recommend "
Taking Care Of Yourself" by Dr Andrew Weil. It explains many aspects of nutrition and health with a heavy dose on vitamins minerals and other nutrients. He explains who needs more or less than RDA and why.
RDA or Recommended Daily Allowance is a general recommendation for the average person. It is not a "maximum allowed" type of thing. Maximums 'doses' of vitamins are known as toxicity levels. Toxicity varies quite a bit from one vitamin to the next. It can also vary from one person to the next for various reasons such as your #2, age, body size, diet (there's vitamins in there too!).
