Egg yolks, beef liver, cheese and fatty fish are the best food sources for natural vitamin D3, according to SFGate. Cod liver oil is also an excellent source of vitamin D3, and fortified milk and orange juice may contain vitamin D2 or D3, depending on the manufacturer. Some yogurts and cereals are also fortified with vitamin D, notes WebMD.
The body produces large amounts of vitamin D3 with the exposure of bare skin to direct sunlight, according to the Vitamin D Council. The body makes as much as 15,000 international units of vitamin D in the time it takes the skin to turn pink. Factors that affect the amount of vitamin D a person gets from sunlight include skin complexion, location, the time of day and the amount of skin exposed to the sun.
Vitamin D plays a critical role in bone health and can reduce risk for stroke, heart disease, diabetes, cancer and autoimmune diseases, reports WebMD. Low levels of vitamin D are associated with rickets, osteoporosis and cognitive impairment in older adults. As of 2010, the recommended daily allowance of vitamin D is 600 international units for people from ages 1 to 70, and 800 international units for adults age 71 and older, states Mayo Clinic.