Vitamin D can be obtained through three different sources: diet, sunlight and dietary supplements. While the risk of consuming too much vitamin D through diet and sunlight is virtually nonexistent, some people can overdose on vitamin D through supplementation. Because vitamin D is a fat-soluble vitamin, excessive consumption can lead to vitamin D toxicity, which can have a number of side effects.
Vitamin D Basics
In fortified supplements and foods, vitamin D is present in two different forms: D-2 and D-3. Both forms of vitamin D can effectively raise the body's levels of vitamin D. This nutrient helps the body absorb calcium and is necessary for bone growth. It also modulates cellular growth and immune function and reduces inflammation. A lack of vitamin D can cause a number of conditions, including brittle bones, osteoporosis and rickets in children.
Doses and Upper Limits
The body cannot overdose on vitamin D through sun exposure, according to the National Institutes of Health. Additionally, vitamin D is not present in food sources in amounts high enough to pose a threat, so an overdose through diet is also highly unlikely. If you are taking a vitamin D supplement, however, the Vitamin D Council notes that anywhere between 10,000 and 40,000 international units of vitamin D per day, when consumed for a matter of months, or a single very large dose, can lead to vitamin D toxicity. The U.S. Food and Drug Administration recommends that infants receive no more than 400 international units of vitamin D per day. The National Institutes of Health recommends 600 international units for adults under age 70.
Effects of Toxicity
To determine if your vitamin D blood serum levels are too high, you can have your blood tested. Because vitamin D aids in calcium absorption, high vitamin D levels in the body can lead to a condition known as hypercalcemia, or high blood calcium. Symptoms of hypercalcemia include feeling sick, tiredness, weakness, poor appetite, confusion, feeling thirsty, diarrhea and muscle pain. If you notice any of the symptoms and you're consuming a vitamin D supplement, you should see your doctor to have your vitamin D serum levels tested.
While vitamin D is not present in many foods, it does occur in significant amounts in fatty fish, such as cod, swordfish, salmon, mackerel and tuna. It can also be found in small amounts in beef liver, egg yolks and cheese. Foods such as milk, yogurt, orange juice and cereal may also be fortified with vitamin D. Cod liver oil can be consumed to obtain vitamin D, too. One tablespoon of cod liver oil contains 340 percent of the daily value of vitamin D. The National Institutes of Health notes that between five and 30 minutes of sun exposure, between the hours of 10 a.m. and 3 p.m., two times per week, without sunscreen, can also provide sufficient vitamin D.
Because certain groups may be at highest risk for vitamin D deficiency, they may also benefit most from vitamin D supplementation. These groups include breast-fed infants, older adults, those with limited sun exposure, people with dark skin, people who have undergone gastric bypass surgery and those with inflammatory bowel disease or other conditions that may interfere with fat absorption.