We hear a lot about vitamin D these days, yet there’s still confusion about its role in health, food sources vs. supplements, and how much we really need for optimum health.
Vitamin D first gained recognition for promoting calcium absorption. Without vitamin D, calcium isn’t well absorbed, and the bones of people who lack vitamin D can become brittle, thin, or misshapen. Adequate vitamin D prevents rickets in children and osteoporosis in adults.
Vitamin D comes in two forms: ergocalciferol (D2), which is found in plants, and cholecalciferol (D3), which is made by the skin when exposed to ultraviolet B sunlight. Food may be fortified with either form. Recent research shows that D3 raises vitamin D levels more effectively, and many clinicians recommend looking carefully at food labels to be sure a product is fortified with this version.
Epidemiological data and early scientific research on animals shows vitamin D’s possible role in preventing or treating type 1 and type 2 diabetes, high blood pressure, and multiple sclerosis. However, too much vitamin D may cause health problems such as loss of appetite, weight loss, heart arrhythmias, and possible damage to the heart, blood vessels, and kidneys from the formation of calcium deposits. It’s unlikely that someone can consume toxic levels of vitamin D from food alone, but overdosing with supplements is a real possibility.
HOW MUCH VITAMIN D DO YOU NEED?
Most experts agree that we can meet at least some of our daily vitamin D needs by exposing bare skin to sunlight. The exact amount of sunlight necessary is unclear and depends on the season, time of day, length of daylight, cloud cover, smog, skin melanin content, and sunscreen use.
The Institute of Medicine’s Food and Nutrition Board develops reference values for vitamins and minerals, including vitamin D. The Recommended Dietary Allowance (RDA) is the average daily amount that meets the requirements of 97% to 98% of healthy people. The RDA for vitamin D is set based on minimal sun exposure and it provides the amount of the vitamin healthy people need from foods and/or supplements to maintain bone health. The RDA for vitamin D is 600 IU for people younger than the age of 70 and 800 IU for those older than age 70.
The Tolerable Upper Intake Level is the maximum daily intake from foods and supplements combined that is unlikely to cause negative health effects.
Unless your doctor recommends higher levels, make sure you don’t exceed this level of vitamin D. (See the Tolerable Upper Intake Level sidebar.)
To meet your daily needs, combine foods containing or fortified with vitamin D to meet the daily recommendation. For example, 3 cups of milk, 1 cup of fortified orange juice, and 3 ounces of cooked sockeye salmon meet the 600 IU-recommendation for a healthy adult. If you routinely fall short, take 400 IU of a D3 supplement. Your bones will thank you.
FOOD SOURCES OF VITAMIN D
There are only a few foods that naturally contain vitamin D: fatty fish such as salmon, tuna, and mackerel; fish liver oils; beef liver; egg yolks; and some types of mushrooms. Mushrooms contain vitamin D2, while the other sources contain vitamin D3. This list specifies the amount of vitamin D in these items:
Cod liver oil, 1 tablespoon: 1,360 IU
Cooked swordfish, 3 ounces: 566 IU
Cooked sockeye salmon, 3 ounces: 447 IU
Tuna packed in water, 3 ounces: 154 IU
Canned sardines in oil, 2 sardines: 46 IU
Cooked beef liver, 3 ounces: 42 IU
1 large egg yolk: 41 IU
Cooked white mushrooms, 3 ounces: 21 IU
Vitamin D was first added to milk in the 1930s to combat rickets, which was a major health problem at the time. One hundred IU of vitamin D continues to be added to most fluid milk sold in the United States; however, dairy products such as cheese, ice cream, and yogurt are not automatically fortified.
Orange juice and breakfast cereals often are routinely fortified with vitamin D. Look for the percent daily value (%DV) on food labels to find out how much vitamin D is present in a particular item. One hundred percent of the daily value is 400 IU, so if a food contains 20% of the DV, there is 80 IU of vitamin D per serving (0.2 X 400 = 80).
TOLERABLE UPPER INTAKE LEVEL
Ages 1 to 3: 2,500 IU
Ages 4 to 8: 3,000 IU
Age 9 and older: 4,000 IU
PREPARED FOODS FORTIFIED WITH VITAMIN D
Kellogg’s Raisin Bran, 1 cup: 10% DV
Cheerios, 1 cup: 10% DV
Total, 1 cup: 25% DV
Florida’s Natural orange juice, 1 cup: 25% DV
Silk Original soymilk, 1 cup: 30% DV
Almond Breeze Original almond milk, 1 cup: 25% DV
Yoplait Light yogurt, 6 ounces: 20% DV
Yoplait Original yogurt, 6 ounces: 50% DV
Stonyfield Original yogurt, 6 ounces: 20% DV
Dannon Activia yogurt, 4 ounces: 10% DV