In the preface to the first edition of this book, I wrote that one stimulus to write it had been teaching a course on nutritional biochemistry, in which my students had raised questions for which I had to search for answers. In the intervening decade, they have continued to stimulate me to try to answer what are often extremely searching questions. I hope that the extent to which helping them through the often conflicting literature has clarified my thoughts is apparent to future students who will use this book and that they will continue to raise questions for which we all have to search for answers.

The other stimulus to write the first edition of this book was my membership of United Kingdom and European Union expert committees on reference intakes of nutrients, which reported in 1991 and 1993, respectively. Since these two committees completed their work, new reference intakes have been published for use in the United States and Canada (from 1997 to 2001) and by the United Nations Food and Agriculture Organization/World Health Organization (in 2001). A decade ago, the concern of those compiling tables of reference intakes was on determining intakes to prevent deficiency. Since then, the emphasis has changed from prevention of deficiency to the promotion of optimum health, and there has been a considerable amount of research to identify biomarkers of optimum, rather than minimally adequate, vitamin status. Epidemiological studies have identified a number of nutrients that appear to provide protection against cancer, cardiovascular, and other degenerative diseases. Large-scale intervention trials with supplements of individual nutrients have, in general, yielded disappointing results, but these have typically been relatively short-term (typically 5–10 years); the obvious experiments would require lifetime studies, which are not technically feasible.