Vitamin D

The primary function of vitamin D is to assist the body in properly absorbing calcium. Fortified milk is a primary source of vitamin D as it goes hand in hand with calcium. Vitamin D is fat-soluble and therefore can be stored in the body for later use.

Vitamin D benefits

The absorption of calcium into the body is essential for bone health. Vitamin D is the catalyst to aid the body in this absorption. Beyond bone health, vitamin D also plays a role in muscle movement by providing nerves a way to carry messages from the brain to the body. It also helps the immune system defend against bacteria and viruses.

Sources of vitamin D

The best natural sources of vitamin D are fatty fish like salmon, tuna, and mackerel. Some cheeses, egg yolk, and livers contain small amounts of vitamin D. Mushrooms are also a natural source of vitamin D. The majority of people receive their vitamin D from fortified foods such as milk, orange juice, yogurt, and soy beverages.

The sun provides the body with vitamin D as well. To maximize vitamin D amounts, it must be a clear day and there should be no barriers between the skin and the sun, i.e., windows. This can be a slippery slope for some as over exposure to sunlight can have damaging effects on the skin and lead to skin cancer.

Recommended amounts

Set forth by the Food and Nutrition Board at the Institute of Medicine, the recommended daily allowances (RDAs) for vitamin D are below (some individuals may be placed on a plan that requires higher than normal amounts to manage a specific issue they may be experiencing).

Table 1: Recommended Dietary Allowances (RDAs) for vitamin D1
Age	Amount
0-12 months	400 IU/day
1-13 years	600 IU/day
14-18 years	600 IU/day
19-70 years	600 IU/day
71+ years	800 IU/day
Pregnant or Nursing Females	600 IU/day

Too much vitamin D can lead to nausea, vomiting, poor appetite, constipation, weakness, and weight loss. Excess amounts of vitamin D can also lead to kidney stones.

Vitamin D deficiency

Depending on your age group, a vitamin D deficiency can result in rickets in children or osteoporosis / osteomalacia in adults. In essence, these conditions are a softening and weakening of the bones. When this occurs, bones are more likely to bow or fracture when compared to healthy, solid bones.

Sources:
¹Vitamin D - http://ods.od.nih.gov/factsheets/VitaminD-QuickFacts/

Vitamin D - All Information - http://www.umm.edu/ency/article/002405all.htm