Approximately 50% of . citizens are Vitamin D deficient. The numbers are higher among hispanic and black populations. The melanin in darker-skinned people interferes with the synthesis of the vitamin D that starts at the level of the skin when the sun comes into contact with it. Therefore, darker-skinned people tend to be more deficient. Vitamin D is crucial for good health , and may be one of the simplest solutions to a wide range of health problems, from diseases of the eyes to the bowels, and conditions rooted in chronic inflammation and immune dysfunction in particular. It is a common deficiency worldwide, even in sundrenched areas, yet many people, including physicians, are unaware they may be lacking this important nutrient.
Rodents are somewhat more susceptible to high doses than other species, and cholecalciferol has been used in poison bait for the control of these pests. It has been claimed that the compound is less toxic to non-target species. However, in practice it has been found that use of cholecalciferol in rodenticides represents a significant hazard to other animals, such as dogs and cats. "Cholecalciferol produces hypercalcemia, which results in systemic calcification of soft tissue, leading to renal failure, cardiac abnormalities, hypertension, CNS depression, and GI upset. Signs generally develop within 18-36 hr of ingestion and can include depression, anorexia, polyuria, and polydipsia." 
Structural relationship of vitamin D 3 (cholecalciferol) and vitamin D 2 (ergocalciferol) with their respective provitamins, cholesterol, and a classic steroid hormone, cortisol (see inset box). The two structural representations presented at the bottom for both vitamin D 3 and vitamin D .2 are equivalent; these are simply different ways of drawing the same molecule. It is to be emphasized that vitamin D 3 is the naturally occurring form of the vitamin; it is produced from 7-dehydrocholesterol, which is present in the skin, by the action of sunlight (see Figure 2). Vitamin D 2 (which is equivalently potent to vitamin D 3 in humans and many mammals, but not birds) is produced commercially by the irradiation of the plant sterol ergosterol with ultraviolet light.