Vitamin D

Vitamin D is important to the body for many different reasons. It works closely with calcium to build and maintain strong bones. Additionally, vitamin D is found in cells throughout the body and is needed for proper nerve function as well as a healthy immune system.

There have been some interesting studies recently on vitamin D and its role in helping prevent diseases like diabetes, hypertension, some autoimmune conditions, and cancers like colon, breast and prostate.

Given it’s important role in health and well-being, it is clear that we need to get the proper amount of vitamin D in our eating plans. But how much vitamin D do we need each day? It actually depends on our age. The requirement for adults aged 19 to 70 years is 600 IU (International Units) per day. This is equivalent to 15 mcg per day. For adults over 70 years, the requirement increases to 800 IU per day (20 mcg).
It can sometimes be difficult to get the required amount of vitamin D from foods each day, as few foods actually contain vitamin D naturally. However, some foods have been fortified with vitamin D. The best food sources of vitamin D include:
  • Fatty fish (salmon, tuna, mackerel). In fact, one 3-oz serving of salmon can provide about 447 IUs of vitamin D.
  • Beef liver, mushrooms and egg yolks provide small amounts. For example, one large egg yolk provides about 41 IUs of vitamin D.
  • Milk and milk alternatives are usually fortified with vitamin D. For example, one cup of low-fat milk provides about 120 IUs of vitamin D.
  • Many yogurts and margarines are fortified with vitamin D. One 6-oz serving of yogurt may contain about 88 IUs of vitamin D. Some yogurts may contain more than this. Similarly, one tablespoon of margarine can contain about 60 IUs of vitamin D.
  • Fortified breakfast cereals may also contain some vitamin D. Usually, one serving of cereal can contain about 40 IUs of vitamin D, but this can vary.
In addition to food sources, our bodies have the ability to make vitamin D when our skin is directly exposed to the sun. Many of us can get at least some of our vitamin D in this way. However, cloudy days, shade, and having dark-colored skin all reduce the amount of vitamin D the skin makes. Additionally, too much exposure of skin to sunlight can lead to increased risk for skin cancer.
How do you know if you are deficient in vitamin D? There is a test that checks vitamin D levels in your blood (the test actually checks levels of a form of vitamin D called 25-hydroxyvitamin D). Generally, blood levels below 30 nmol/L are tool low for bone or overall health. Levels above 125 nmol/L are too high. For most people, levels greater than 50 nmol/L are sufficient. If you are concerned that your vitamin D levels may be too low, ask your physician or health care professional to have your blood levels checked.
If you don’t have much exposure to direct sunlight, find you aren’t including foods that contain vitamin D, or are tested and found to be low in vitamin D, you might want to consider taking a supplement that includes vitamin D. Be cautious about taking large doses, however. Vitamin D can build up to toxic levels in the blood and cause symptoms like nausea, vomiting, poor appetite, weakness, constipation, and can affect the kidneys. This toxicity is almost always the result of overuse of supplements. As a result of this toxicity, there is a safe upper limit (UL) for daily intake of vitamin D. For adults, this upper limit is 4,000 IU per day.
As a word of caution, vitamin D can interfere or react with other medications you may be taking. Ask your physician if you have any concerns or questions in this regard.
If you are looking for more information about vitamin D, one of the best resources I have found comes from the National Institutes of Health and their Office of Dietary Supplements. Click here to view a simple fact sheet regarding vitamin D.
Rachel Andrew MPH, RD, CD