Vitamin D is a fat-soluble vitamin that is essential for maintaining good health. It is synthesized in the skin upon exposure to ultraviolet light, and it is added to milk, orange juice, and other foods. Most people do not spend much time worrying about whether they are getting enough vitamin D or which form of vitamin D is best. With the arrival of fall and shorter days, a good review of vitamin D is appropriate.
Why do we need vitamin D?
Vitamin D aids in the absorption of calcium from the small intestine. A deficiency of vitamin D will result in less calcium in the blood. Vitamin D also plays less important roles in the mineralization of bone.
Lower calcium in the blood will corrected by the removal of calcium from the skeleton/bones. In children, calcium deficiency can result in rickets and often is seen as a bowing of the legs (“bow-legged”).
In adults, vitamin D deficiency can cause a condition called osteomalacia and a decreased bone mineral density (“thinning” of the bones). This puts certain people at risk for fractures, especially elderly women.
How can a vitamin D deficiency occur?
• Not enough sunlight – this can occur when not enough time is spent outdoors, as well as with the use of sunblock
• Absorption problems – this can occur in those with celiac sprue, short bowel syndrome, and cystic fibrosis
• Medications – some medications, such as Dilantin, phenobarbital, and rifampin can cause the liver to break down vitamin D at an accelerated rate, and some drugs, such as orlistat, impair vitamin D absorption
• Inadequate intake
Which type of vitamin D is best?
Vitamin D exists is 2 different forms. Vitamin D2 is called ergocalciferol and is made by irradiating yeast with ultraviolet radiation.
Vitamin D3 is called cholecalciferol. This is the form that is created in the skin as a result of ultraviolet radiation exposure (such as the sun).
Ergocalciferol (vitamin D2) is less potent and shorter acting than cholecalciferol (vitamin D3).
Often, the type of vitamin D found in a food is not disclosed, making it impossible to determine whether it is D2 or D3.
When buying a supplement, look at the active ingredients on the label. The label should state which form of vitamin D is within.
How much vitamin D is needed daily?
Vitamin D is measured in International Units (IUs). The Institute of Medicine updated the daily recommended intake of vitamin D at the end of 2010. The new recommendations are based on minimal sun exposure.
Most people in North America require 400 IU daily, usually no more than 600 IU daily. Those 71 years of age and older may require as much as 800 IU per day.
Vitamin D is not found naturally in many foods. Small amounts can be found in beef liver, cheese, and egg yolks.
Since vitamin D is fat-soluble, the body will store excess vitamin D in the fat. It is rare to have too much vitamin D in the body, but supplementing with extremely high doses can cause vitamin D toxicity. Symptoms include nausea, vomiting, constipation (possibly alternating with diarrhea), weakness, weight loss, tingling sensation in the mouth, confusion, and heart rhythm abnormalities.