People tend to get 90% of their vitamin D from sunlight exposure, but diet is also an important way of getting vitamin D, especially for those who live in the higher northern latitudes where sun exposure is more limited. How much vitamin D should be obtained from your diet is a contentious question.

The current recommended daily amounts are:

• 5 mcg (200 IU) for people aged 19-50
• 10 mcg (400 IU) for those aged 51-69
• 15 mcg (600 IU) for those over 70

However, because the benefits and functions of vitamin D in the body have only recently begun to be investigated, how much of the nutrient is necessary for optimal health is not really known.

One cup of vitamin D fortified milk provides about one-fourth of the current estimated daily requirement in adults - although remember this requirement is possibly too conservative. Only a small number of foods, such as fatty fish and fish oils, contain naturally high amounts of vitamin D. Vitamin D supplements and multivitamins can also be taken to increase vitamin D levels.

Check this table to compare food sources of vitamin D:

Source: National Institutes of Health, adapted by Joan Bushman, MPH, RD.
** Based on 2000 calorie diet.

Be aware that because vitamin D is a fat-soluble vitamin, it is stored in the body and has the potential to reach toxic levels if taken in high doses for prolonged periods of time, particularly in supplement form. Vitamin D toxicity can cause vomiting, nausea, poor appetite, constipation, weakness, weight loss, confusion, skin rash, headaches, muscle weakness, calcium deposits and kidney stones. Prolonged sunlight exposure does not cause buildup of vitamin D as the body down-regulates its production when body levels are adequate - but it's not good for your skin!

Also be mindful that some things interfere with vitamin D absorption from foods, including mineral oil, antacids, cortisone, liver and gall bladder disorders, and some cholesterol lowering drugs.

Infants. Vitamin D supplements are often recommended for exclusively breast-fed infants because human milk may not contain adequate vitamin D. Mothers who have limited sun exposure and who are exclusively breastfeeding their infants should consult with their doctor.

Children and adolescents who consume few vitamin D food sources or who spend a lot of time indoors are at a higher risk for weakened bones and stunted growth. This can make them vulnerable to fractures and osteoporosis in later life.

People over the age of 50. As we age, the ability of skin to convert vitamin D to its active form decreases. Additionally, the kidneys, which help change vitamin D to its active form, sometimes do not work as well with aging.

Menopausal and post-menopausal women are also at greater risk for osteoporosis. During menopause the estrogen balance is changed resulting in more bone being broken down than rebuilt. Vitamin D, in addition to calcium, is a vital nutrient during this time.

People who are obese. Jacobo Wortsman, MD, and co-authors compiled a study that indicated that in the obese body, vitamin D might be stored differently than in the lean body. They speculated that with obesity, the increased fat stores remove the vitamin D from the bloodstream where it otherwise would be available for use.

People with digestive problems. Individuals who have reduced ability to absorb dietary fat may need extra vitamin D because it is a fat-soluble vitamin.