Your body has the capacity to produce all the vitamin D it needs from sensible sun exposure. Factors that effect your skins ability to produce vitamin D include the time of day, time of year, weather, how far you live from the equator, amount of clothing worn and skin tone.
Under ideal conditions (summer time in the tropics with torso exposed), the human body can produce 10,000 IU of vitamin D in as little as 30 minutes. However, due to the nature of modern life, most people do not get enough sun exposure to meet their vitamin D requirements. This is particularly true for people living at higher latitudes and people with darker skin.
There are food sources of vitamin D, but it can be difficult to increase your vitamin D levels through diet alone, so in many cases, supplementation with vitamin D3 may be necessary.
The table below shows commonly available foods with the highest levels of vitamin D: