The primary role of vitamin D in the human body is to promote the process of bone mineralization. While calcium and other minerals are the building blocks of healthy bones, it is vitamin D that regulates their actions in the body and makes them available for absorption into bone.

Vitamin D is different from all other nutrients in that it can be produced in the body with the help of sunlight. With 10-15 minutes of direct sunlight each day, the human body can produce enough vitamin D to satisfy its daily requirements. This simple way of obtaining adequate vitamin D is complicated by the need for daily exposure to the direct sun, and by conditions that limit vitamin D absorption such as smog, clouds, darker skin, high altitude, and skin lotions.

Not Enough Vitamin D. Without sufficient quantities of vitamin D, the body cannot appropriately direct the actions of calcium into bone. Rather, in the absence of adequate vitamin D, calcium will move out of the bones; over time, this calcium drain will cause loss of bone mass and weakening of the skeletal structure, leading to increased risk of fractures, reduced ability to heal damaged bones, and ultimately, osteoporosis.

Sources of Vitamin D. Vitamin D can be easily obtained from our diets as well as from sunlight. Milk and margarine are generally fortified with vitamin D, as are many other foods, and it occurs naturally in significant amounts in eggs, liver, and fish.

Most of our vitamin D needs can be met with the regular consumption of milk products that are fortified with the vitamin. Eggs, meat, and fish provide ample quantities of vitamin D for persons who do not drink milk. Because there is no vitamin D in plant foods, vegetarians should take care to obtain appropriate amounts of vitamin D either through milk products or daily multiple vitamins.

As with all vitamins, it is important that adequate amounts of vitamin D be consumed on a daily basis to meet the body’s needs. Vitamin D does not have to be consumed at the same time as calcium to effectively regulate calcium actions ~ it simply needs to be present in the diet on a regular basis, along with their individual and shared functions in the body.

Too Much Vitamin D. Because vitamin D is a “fat-soluble” vitamin, it is not easily broken down for use by the body. If consumed in excess, it can accumulate in soft tissues such as the kidney and result in kidney damage, which in turn can cause increased amounts of calcium to be removed from bones.

The amounts of vitamin D that are present in foods are well within the recommended limits, and do not pose problems in terms of vitamin D excess. Vitamin D toxicity becomes a concern when the vitamin is taken in concentrated form or supplement. Thus, vitamin D intake is best maintained at about the recommended dietary allowance (RDA) of 400 international units (IU) each day.