We get our supply of vitamin D in two ways: from the food we eat and from a hormone our bodies make when we stay under the sun. There are only a few food options that are naturally rich in vitamin D, that is why the biggest dietary sources of vitamin D are fortified food and vitamin supplements.

Good sources of vitamin D include dairy products and breakfast cereals, both of which are fortified with vitamin D, as well as fatty fish like salmon and tuna.

For most people, the best way to get enough vitamin D is by taking a supplement, although the level in most multivitamins, which is usually 400 IU, is too low.

Fortunately, some manufacturers have begun adding 800 or 1,000 IU of vitamin D to their standard multivitamin preparations. If the multivitamin you take does not have 1,000 IU of vitamin D, you may want to consider adding a separate vitamin D supplement, especially if you do not spend much time in the sun.

The body also manufactures vitamin D from cholesterol, through a process triggered by the action of sunlight on the skin. This is actually the reason why vitamin D is also referred to as the ’sunshine vitamin’.

Yet, some people do not make enough vitamin D from the sun. These people are those who have a darker skin tone, who are overweight, who are older, and who cover up when they are under the sun.

Correctly applied sunscreen reduces our ability to absorb vitamin D by more than 90 percent. And not all sunlight is created equal: The sun’s ultraviolet B (UVB) rays, the so-called ‘tanning rays’, and the rays that trigger the skin to produce vitamin D are stronger near the equator and weaker at higher latitudes. Hence, in the fall and winter seasons, people who live at higher latitudes, such as in the northern part of the U.S. and Europe, cannot make much vitamin D from the sun.

Many of the body’s organs and tissues have receptors for vitamin D, which helps ensure that the body absorbs and retains calcium and phosphorus that are critical for building bones. Vitamin D also reduces cancer cell growth and plays a critical role in controlling infections. Several promising areas of vitamin D research look far beyond its role in building bones.

Several studies link low vitamin D levels with an increased risk of fractures in older adults, and they suggest that vitamin D supplementation may prevent such fractures, as long as it is taken in a high enough dose.

The latest evidence comes from a combined analysis of several fracture prevention trials that included thousands of elderly people, most of which are women. It was found out that taking at least 800 IU of vitamin D supplements per day reduces hip and non-spine fractures by 20 percent.

Vitamin D may also help increase muscle strength, which in turn helps in preventing falls, a common problem that leads to substantial disability and death in older people. Taking 700 to 1,000 IU of vitamin D per day lowers the risk of falls by 19 percent, but taking only 200 to 600 IU per day did not offer any such protection.