Vitamin D


Vitamin D

Frequently Asked Questions

by Sarah Washburn, M.S., R.D., Nutrition Department, Seattle Cancer Care Alliance

Did you know that a vitamin D deficiency or insufficiency might be associated with risk of cancer progression or recurrence?  Other potential consequences of vitamin D deficiency include decreased bone density or osteoporosis, muscle weakness, bone tenderness or pain, autoimmune diseases, osteoarthritis, diabetes and cardiovascular disease.  Here is some helpful information regarding vitamin D:

How is my vitamin D level measured?

The major marker to determine your vitamin D level in your blood is 25-hydroxyvitamin D (25-OH vitamin D).  This is a simple blood test that costs about $60, although the price can vary.

What is an optimal 25-OH vitamin D level?

A 25-OH vitamin D level of 30 to 80 nanograms per milliliter (ng/mL) is considered sufficient or optimal, depending on what study you read.  Refer to the Grassroots Health web site (see reference below) to view a chart displaying optimal vitamin D levels and associated health conditions.  A level of 20 to 29.9 ng/mL is considered insufficient as it is associated with metabolic changes that can be early signs of a vitamin D deficiency.  Finally, a 25-OH vitamin D level < 20 ng/mL is considered a vitamin D deficiency.

What are my vitamin D requirements?

The current National Institute of Health (NIH) recommendations are 200 International Units (IU) for adults between the ages of 19 and 50 years, 400 IU per day for adults between the ages of 51 and 70 years and 600 IU for adults over 70 years old.  However, the Office of Dietary Supplements at the NIH has assigned a group of experts to review the current literature and it is anticipated that these recommendations will change.   Most vitamin D experts estimate that the requirements will increase to 1,000 to 2,000 IU per day for most adults. 

How do I get vitamin D?

Vitamin D is known as the sunshine vitamin because our skin produces an abundant amount of vitamin D via ultraviolet light.  Reasonable sun exposure is the most inexpensive and natural way to meet your vitamin D requirements.  However, current studies indicate that 50% to 60% of the US population is vitamin D insufficient or deficient due to limited sun exposure, constant use of sunscreen, aging, obesity (vitamin D gets trapped in fat tissue) and living more than 40 degrees North of the equator (Seattle latitude is 48 degrees North).  Experts recommend that we take 15 to 30 minutes most days to expose our arms and legs to the sun before applying sunscreen.  Individuals with darker skin (due to greater melanin content) will require longer sun exposure to produce the same amount of vitamin D as individuals with lighter skin.  Make sure to apply sunscreen after a brief exposure to the sun without sunscreen.   

Since adequate sun exposure is hard to come by for about 6 months out of the year in the Seattle area, we need to rely on eating foods that contain vitamin D and/or take a vitamin D supplement to maintain our vitamin D levels.  Unfortunately, very few foods naturally contain vitamin D, although there are some foods that are fortified with vitamin D (see the list below).  Don't rely on cod liver oil as a routine vitamin D source due to its excessive vitamin A content.  According to the last US population study from the Centers for Disease Control, the average intake of vitamin D from food alone was less than 240 IU per day.  Therefore, a vitamin D supplement is often recommended. 

Food Serving Size Approximate Vitamin D per serving (IU)
Many cold cereals ~1 cup 40
Milk (with various fat contents) 1 cup 100
Yogurt (cow's milk) 1 cup 80 - 100
Soy milk, vanilla 1 cup 120
Almond milk 1 cup 100
Egg 1 large 26
Soy nuts 1 ounce 100
Mushrooms, common white ½ cup 53
Mushrooms, shiitake, dried 4 mushrooms 249
Mackerel, cooked 3.5 ounces 345
Halibut, cooked 3 ounces 510
Salmon, cooked 3.5 ounces 360
Shrimp, cooked 3 ounces 129
Tuna fish, canned in oil 3 ounces 201
Cod liver oil 1 teaspoon 453

Vitamin D supplements come in 2 forms:

  1. Ergocalciferol (D2) which is made from plants and fungus
  2. Cholecalciferol (D3), which is make from fish oil or lanolin from sheep sweat glands

D3 has 3 times the potency of D2, but most recent studies have not shown that D3 is superior to D2 in preventing fractures.  Over-the-counter D2 and D3 supplements are generally available in 400 to 10,000 IU tablets, capsules or drops.  And, multivitamins often contain 400 IU of vitamin D. 

It is best to have your 25-OH vitamin D level checked once or twice a year to determine your supplementation requirements.

There are some concerns regarding vitamin D supplementation for individuals with medical conditions that cause a high calcium level in the blood and for individuals on certain medications, so check with your health care professional before taking more than 1,000 to 2,000 IU of vitamin D per day.  Prescription vitamin D (usually 50,000 IU capsules taken once a week for 6 to 12 weeks) may be required to stabilize your blood level if you have a vitamin D deficiency. 


Frequently Asked Questions  

Q. What is Vitamin D?

Vitamin D (cholecalciferol) is a fat-soluble vitamin that helps maintain blood levels of calcium by increasing absorption from food and reducing urinary calcium loss. Both functions help keep calcium in the body and therefore spare the calcium that is stored in bones. Though the overall effect of vitamin D on the bones is complicated, it is certainly necessary for healthy bones and teeth.

While Vitamin D is present in some foods, it is also produced by the human body during exposure to the ultraviolet rays of the sun. However, seasonal changes, latitude, time of day, cloud cover, smog and sunscreen can all affect UV exposure. Vitamin D deficiency is more common in northern latitudes, making vitamin D supplementation more important for residents of those areas.

Vitamin D plays a role in immunity and blood cell formation and also helps cells differentiate - a process that may reduce the risk of cancer. From various studies, researchers have hypothesized that vitamin D may protect people from multiple sclerosis, autoimmune arthritis and juvenile diabetes. Vitamin D is also necessary for maintenance of adequate blood levels of insulin. Vitamin D receptors have been found in the pancreas, and some evidence suggests that supplements may increase insulin secretion for some people with adult-onset diabetes.