Summarize this article:

There are very few foods that are naturally high in vitamin D. If you can find some that are and consume them on a regular basis, you will optimize your body's ability to naturally absorb vitamin D. Foods that are naturally high in vitamin D include:  Salmon Tuna Mackerel Sardines Cod liver oil Eggs, cheese, and beef liver contain small amounts of vitamin D Because foods that naturally contain vitamin D are hard to come by, there are regulations in many places in the world (including the United States and Canada) that certain foods be fortified with vitamin D prior to being sold at the grocery store. Foods fortified with vitamin D compose the majority of vitamin D in most people's diets. These foods include:  Milk Margarine Some breakfast cereals Some brands of orange juice Some bread products Some yogurt Everybody can benefit from a high-quality vitamin D3 supplement, which allow you to benefit without risking skin damage from sun exposure. Unfortunately, the current RDA's are very low to benefit the body and there is no consistent agreement among health organizations about how much to take. The maximum daily safe dose for adults is 4,000 IU (though some research suggests that 10,000 IU may still be safe). Infants and children should take lower doses (0–6 months, maximum 1,000 IU; 7–12 months maximum 1500 IU; 1–3 years maximum 2500 IU; 4–8 years maximum 3,000 IU).  These recommendations may also change if you have an illness that interferes with your body's natural ability to absorb vitamin D. Consult your doctor if you need a higher dose. Always take vitamin D3 (cholecalciferol), not Vitamin D2. Vitamin D2 is poorly absorbed.  Remember that other supplements such as multivitamins and fish oil can contain vitamin D. Be sure to factor that in to ensure that you do not take too much. You can get both flavored and flavorless supplements that are drops. Sometimes, one oral drop = 1,000 IU. This makes it easy to supplement with vitamin D.

Summary:
Consume foods that are naturally high in vitamin D. Choose foods that have been fortified with vitamin D. Ensure that you are consuming the daily recommended amount of vitamin D.