Vitamin D deficiency has emerged as a potential risk factor for multiple adverse outcomes,
including cardiovascular and cancer related morbidity and mortality. Epidemiological studies have been
instrumental in detecting associations between lower serum levels of vitamin D and such outcomes, and
by doing so have provided an impetus to examine the mechanisms of action underlying such
associations and to design interventional trials of vitamin D supplementation to try and reverse the
adverse effects attributed to low serum vitamin D. This chapter reviews in detail observational studies
that describe the incidence and prevalence of hypovitaminosis D, and the various adverse outcomes that
low serum vitamin D has been linked with. The comprehensive nature of this review will provide the
reader with a better understanding of why vitamin D is currently regarded as a very promising area of
research to try and lower adverse outcomes in a variety of patient groups and in the general population.
Keywords: All-cause mortality, cardiovascular risk factors, cardiovascular outcomes, cause-specific
mortality, epidemiology, malignancies, hypovitaminosis D, National Health and Nutrition Examination
Survey (NHANES), vitamin D supplementation.
