Vitamin D-3 is the naturally occurring form of vitamin D and helps the body to absorb calcium to keep bones strong, according to The Merck Manual Professional Edition. It is also helpful in preventing diabetes, cancer and high blood pressure, reports WebMD.
While the body produces vitamin D naturally with sun exposure, many people do not receive enough sunlight to make enough of the vitamin to meet their daily recommend requirement, indicates WebMD. Many people living in northern regions of the United States are low in vitamin D when the days grow short, even with the recommend amount of sun exposure. Invalids and people who spend most of their time indoors benefit from supplements.
The lack of vitamin D production correlates to the increase in certain types of cancer among residents who live in the northern latitudes. WebMD indicates supplemental vitamin D-3 helps to reduce their risk.
While overdosing on vitamin D produced through the skin is impossible, supplements carry the risk of an overdose. Vitamin D is a fat-soluble vitamin that the body does not excrete in the urine. Exceeding the 2,000 international units daily has the potential of toxic build-up causing kidney stones and excessive bleeding, according to WebMD.