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Vitamin D: What it does, how much you need

Kelsey M. Mangano M.S., R.D. [April 12 2012]

Vitamin D's importance and how it affects one's health remain a popular health topic since new guidelines were established in 2010. There has been much debate over how much vitamin D is enough for general health and whether some groups of people need more than others.

What is vitamin D?
There are two types of vitamin D: calcidiol (vitamin D2) and calcitriol (vitamin D3). Vitamin D2 is produced in the skin after sun exposure and is also in certain foods. Vitamin D2 converts to vitamin D3 in the kidney and is the vitamin form the body uses. Vitamin D is fat-soluble and its many functions include promoting calcium absorption, maintaining adequate levels of calcium and phosphate and promoting bone growth and life-long bone health.

How much vitamin D is needed?
A 2010 Institute of Medicine report noted that persons are at risk of vitamin D deficiency when vitamin D blood levels are below 30 and that some individuals are potentially at risk for inadequacy at levels ranging from 30-50. These recommended blood levels are important for general health and to help prevent bone diseases like osteoporosis. The report also included these guidelines for recommended daily vitamin D intakes, which vary depending on age: 0 to 12 months, 400 international units (IU); 1 to 70 years old, 600 IU; and greater than 70 years old, 800 IU.
Numerous studies are being conducted to evaluate the potential relationship between vitamin D and other diseases (e.g., cancer, diabetes and multiple sclerosis). Taking extra vitamin D may not benefit health and may cause harmful effects when taken at toxic levels. Persons over age 9 should not consume more than 4,000 IU daily.
Very few foods contain vitamin D. Fatty fish such as salmon, tuna and mackerel are very good sources; three ounces provide about 500 IU of vitamin D per serving. One tablespoon of cod liver oil provides the most vitamin D per serving with 1,360 IU. A one-cup serving of fortified foods like milk and orange juice provides about 115-130 IU of vitamin D. Most people obtain some vitamin D from sun exposure by conversion in the skin. However, from November to March in New England the sun is not strong enough for the skin to make vitamin D. Therefore, vitamin D needs must be met through the diet. Over-the-counter vitamin D supplements are another option for those persons avoiding direct sunlight. However, always discuss the use of new supplements with your doctor or a dietitian before use.

Registered dietitian Kelsey M. Mangano works at The Hospital of Central Connecticut (HOCC) Department of Food and Nutrition. For information about nutrition counseling with an HOCC registered dietitian, please call 860 224 5433. at http://www.thocc.org/wellness/. Learn more about hospital nutrition and wellness programs