Don't Forget Your Vitamin D!

Julie Redfern, L.D., R.D.N., and Angela Illing
Brigham and Women's Hospital
Previously published on Intelihealth.com, June 24, 2005
Reviewed October 2009
Click here for a printable format.

• The Sunshine Vitamin
• Vitamin D for Health
• How Much is Enough?
• How Does Your Vitamin D Add Up?
• A Word About Supplements
• The Bottom Line

The Sunshine Vitamin

When you step out into sunlight, you're getting more than just a tan. When the ultraviolet B rays from
the sun come in contact with your skin, they activate a series of reactions whose end product is a
hormone. This hormone, 1,25 dihydroxyvitamin D3, is more commonly known as "vitamin D." In
addition to sunlight, vitamin D is found naturally in some food sources such as egg yolks, herring
and cod liver oil, and it is added to other foods such as milk.

Many years ago, when humans lived near the equator, they spent a great deal of time outside with much
of their skin exposed to the sun. They did not use sunscreen, and vitamin D deficiency was not a
problem. A fair-skinned person whose face and hands are exposed to sunlight could produce 10,000
to 12,000 international units (IU) of vitamin D. However, many factors are making it harder for people to
get adequate vitamin D from sunlight. Some live in parts of the world where the sun doesn't shine brightly.
For example in Boston, from November to February, it's almost impossible to get adequate vitamin D from
sunlight alone. In addition, concerns about sun damage and skin cancer have led to increased sunscreen
use. Just an SPF of 8 decreases vitamin D production by more than 95%. Also, if you are older than 70 or
are dark-skinned, you will need longer sun exposure to convert vitamin D in the skin to its active form.

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Vitamin D for Health

Vitamin D has long been known to be crucial for bone health, helping the body to better absorb calcium
and thereby preventing bone diseases such as rickets in children and osteoporosis in adults. New
research is suggesting that vitamin D may do much more than help with healthy bones. It likely aids
in protecting muscle strength and preventing falls as we age. In addition, newer studies show it has
a positive role in preventing cancer, diabetes and autoimmune diseases such as multiple sclerosis,
lupus and inflammatory bowel disease.

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How Much is Enough?

Cases of rickets in children appear to be on the rise in the United States, and current research
suggests most American adults are deficient in vitamin D for at least part of the year. The Institute
of Medicine of the National Academy of Sciences currently recommends that adults get the
following amounts of vitamin D:

• 19-50 years old - 200 IU/day
• 51-70 years old - 400 IU/day
• older than 70 years - 600 IU/day

This level might not be so hard to achieve if you consume foods high in vitamin D. For example, a glass of
milk or vitamin D-fortified orange juice contains 100 IU, and 1 teaspoon of cod liver oil contains 450 IU.
Sometimes labels will have vitamin D in micrograms (mcg) instead of IUs. To convert, 1 microgram
(mcg) = 40 IUs. For example: 5mcg = 200 IUs of vitamin D.

Some scientists suggest these recommendations are entirely too low to have an impact on muscle
strength, diabetes, cancer and autoimmune diseases. And while 200 to 600 IU/day may be
adequate to prevent bone disease, 800 to 1,000 IU/day may be necessary to obtain vitamin D's
effect on these other conditions.

Compared to current recommendations, 800 to 1,000 IU/day seems like quite a high dose. This brings
about the question of toxicity. Vitamin D is a fat-soluble vitamin, which means it is stored in the body's
adipose, or fat tissue, until the fat is metabolized. In very high doses, vitamin D can be toxic and can
lead to serious side effects such as calcium deposits in the heart and other organs. However, the
lowest dose at which an adverse effect has ever been seen was 3,800 IU per day. Based on this finding,
the recommendation for the highest safe level (the "UL," or upper limit) set by the Institute of Medicine is
2,000 IU per day.

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How Does Your Dietary Vitamin D Add Up?

Milk is a common source of vitamin D in the American diet. However, many people don't drink milk
because they are lactose-intolerant, vegan or they just don't like it. Vitamin D is found in other foods,
but not many that are found in the daily diets of most Americans. Atlantic herring, cod liver oil, salmon,
mackerel and canned tuna in oil all have appreciable amounts of vitamin D (see below).

Even for milk drinkers and those who occasionally eat other high-vitamin D foods, aiming for a daily
intake of 800 to 1,000 IU per day can be difficult to achieve from diet alone.

Breast milk has very low amounts of vitamin D, so babies need supplemental vitamin D
if they are exclusively breast fed.

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A Word About Supplements

Vitamin D is also found in supplements. For those who feel they may not be getting enough
vitamin D from foods or sunlight, and you are in one of the high risk groups for deficiencies,
you may consider taking vitamin D supplements. When choosing a supplement, look for one
that contains "cholecalciferol" (vitamin D3) rather than "ergocalciferol" (vitamin D2). The D3,
or "cholecalciferol" form of vitamin D has been shown to be better absorbed and available to
the body.

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The Bottom Line

Vitamin D has long been known to be important for health. It's now attracting attention as we
find new health reasons to support our intake; and we realize this vitamin is deficient in the
diets of many people.

Remember:

• Eat a balanced, healthy diet that includes foods high in vitamin D.
• Spend just 10 to 15 minutes in the sun without sunscreen at least two times per week.
• Include a supplement of vitamin D3 if you're not getting enough sunshine or vitamin D rich foods.
• Take enough vitamin D for your age.
• You may need 800 to 1,000 IU per day if you are dark-skinned, or never in the sun.
• Be sure your total intake of vitamin D from foods and supplements does not exceed 2,000 IUs
  per day, which is the safe upper limit.

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