Vitamin D is essential to bone health; severe and prolonged deficiency can lead to rickets in children and osteomalacia in adults. As the main source of vitamin D is exposure of the skin to ultraviolet rays, it has long been assumed that living in a sunny country ensures adequate vitamin D levels (i.e. the optimum level of serum vitamin D to prevent detrimental effects to bone health). However, there is increasing evidence that vitamin D insufficiency may have been underestimated in low latitude, tropical countries. Brazil is a unique country to study as it is the only country in the world that has both the line of equator and that of the tropic of Capricorn running through its territory. Recent findings of a high prevalence of vitamin D insufficiency in countries, such as Brazil, suggest that vitamin D deficiency may be increasing at a global level. More robust and large studies are needed for an accurate estimate of the prevalence of insufficient vitamin D levels in populations in sunny countries and the relative contribution of key influential factors, such as individual sun exposure, dietary intake, skin pigmentation and lifestyle.