Vitamin D

Vitamin D is a type of steroid vitamin that is responsible for promoting the absorption and metabolism of phosphorous and calcium. Individuals who receive ample sunlight exposure may not require vitamin D supplements due to the sufficient amount of vitamin D synthesis that takes place in the skin when exposed to the sun. There are five total forms of vitamin D that have been discovered to date. Two of those forms appear to be most important to humans. They are vitamins D2 and D3.

Functions of Vitamin D

Vitamin D is important for a variety of reasons, including the following:

  • Critical for metabolism and absorption of phosphorous and calcium, which is crucial for the maintenance of healthy bones
  • Regulator of the immune system
  • May protect the immune system from the common cold and other disorders
  • May reduce the risk for developing multiple sclerosis
  • May present a critical role in helping the brain to continue working properly later in life
  • Likely associated with the maintenance of a healthy body weight
  • Reduce the frequency and severity of asthma symptoms
  • Shown to reduce the risk of developing rheumatoid arthritis in women
  • Could protect the body from damage associated with low levels of radiation exposure
  • May lower the risk for developing cancer
  • May make increase recovery time from tuberculosis
  • May reduce the risk of heart attack and early death

Sources of Vitamin D

1. Sunlight

When the skin is directly exposed to sunlight, the body is able to make vitamin D on its own. For this reason, vitamin D is often referred to as the sunshine vitamin. Most people are able to meet at least some of the requirements for vitamin D through direct sunlight exposure. Exposure to sunlight for 10-15 minutes three times per week is usually enough to produce your body's vitamin D requirements.

Due to the fact that sun exposure can increase the risk of skin cancer, it is important to use sunscreen after more than a few minutes of exposure. If you live in an area that is lacking in sunlight, you may have trouble producing enough vitamin D. Sunlight filtered through a window is not sufficient for vitamin D production. Shade, cloudy days, and dark-colored skin can also reduce the amount of vitamin D your skin is able to produce.

2. Food Sources

Unfortunately, not many foods contain vitamin D on their own. For this reason, many foods are actually fortified with vitamin D. Foods with vitamin D include:

  • Butter
  • Cheese
  • Cream
  • Fatty fish, like salmon, tuna, mackerel
  • Oysters
  • Fortified milk – all milk sold in the United States is fortified with vitamin D
  • Fortified breakfast cereals
  • Soy milk – not all soy milks are fortified, so be sure to check the nutritional label

3. Supplements

Due to the fact that it can be difficult to obtain a sufficient amount of vitamin D from daily diet, many people find it necessary to take supplements. You can find vitamin D in two different forms. They are:

  • D2 (ergocalciferol)
  • D3 (cholecalciferol)

Recommended Dosage of Vitamin D

Recommended Dietary Allowance for Vitamin D




  • 0 - 6 months: 400 IU (10 micrograms (mcg) per day)
  • 7 - 12 months: 400 IU (5 mcg/day)


  • 1 - 3 years: 600 IU (15 mcg/day)
  • 4 - 8 years: 600 IU (15 mcg/day)

Older Children and Adults

  • 9 - 70 years: 600 IU (15 mcg/day)
  • Adults over 70 years: 800 IU (20 mcg/day)
  • Pregnancy and breast-feeding: 600 IU (15 mcg/day)

Upper Limit of Vitamin D




1,000 to 1,500 IU/day


2,500 to 3,000 IU/day for children

Older Children and Adults

4,000 IU/day

Side Effects of Vitamin D Overdose

It is important to understand that excessive levels of vitamin D can cause the intestines to absorb too much calcium. This can result in high levels of calcium, resulting in:

  • Kidney stones
  • Kidney damage
  • Disorientation and confusion
  • Calcium deposits in soft tissues, such as the lungs and heart
  • Nausea, vomiting, poor appetite, constipation, weakness, weight loss