Vitamin D

Vitamin D is an organic compound, that is fat-soluble (meaning some dietary fat is necessary for its absorption).

Why is Vitamin D Important?

Vitamin D is fundamental to bone development and maintenance. Rickets, once a common childhood ailment, is now understood to be caused by vitamin D deficiency and is readily curable as well as avoidable with supplementation and proper nutrition. Recent studies have linked this nutrient to more than just peak bone mass and proper muscle functioning.  Inadequate vitamin D levels are associated with immune deficiency, frequent infection, diabetes, heart disease, prostate cancer, breast cancer, hormone imbalances and osteoporosis.

How Do I Get Vitamin D?

Humans obtain vitamin D from UVB exposure, diet and supplements. UVB rays (290-320 nanometers) convert 7-dehydrocholesterol (7-DHC) in the skin to previtamin D3, which is then converted to vitamin D3. This inactive vitamin D3 travels to the liver and kidneys, where it becomes biologically active.

After limited UVB exposure, (determined by season, time of day, skin type and latitude; approximately five minutes daily for a Caucasian in New York at noontime in summer), cutaneous vitamin D production reaches its maximum, which equals 10-20 percent of the concentration of 7-DHC in the skin. Further UV exposure will progressively increase DNA damage but will not produce more vitamin D. In fact it will actually have the reverse effect, breaking down vitamin D to inactive compounds.

Vitamin D can also be obtained from oily fish (salmon, mackerel, sardines) and cod liver oil as well as from fortified orange juice and milk (both with 100 IU per 8oz), yogurts, and some cereals such as Kashi, Grape Nuts and Total (100 IU per serving). Finally, supplements are readily obtained and inexpensive.

How Much Vitamin D Do We Need?

The Food and Nutrition Board of The National Academies has established daily Adequate Intake (AI) levels for vitamin D at 5 micrograms (mcg), or 200 International Units (IU), for those under age 50; 10 mcg (400 IU) for adults 51-70; and 15 mcg (600 IU) for people 71 and older. On nutritional labels, vitamin D quantity is usually listed as Percent Daily Value (DV). This represents the amount, as a percentage of your vitamin D needs, based on a diet of 2,000 calories.

But even among physicians there is uncertainty about how much Vitamin D is necessary. Several studies suggest that even 20 mcg (800 IU) of vitamin D may be insufficient to prevent low bone density. If your physician approves, consider increasing your intake. The Office of Dietary Supplements has established tolerable upper intake levels for vitamin D at 25 mcg, or 1,000 IU, for babies under one year old; and 50 mcg, or 2,000 IU, for everyone else. While rare, vitamin D toxicity can cause nausea, weakness, and raised blood levels of calcium, which may lead to mental confusion and heart rhythm problems.

Certain medications can impair vitamin D or calcium absorbency. Consult your doctor about vitamin D intake if you take any medications regularly.

Good Sources of Vitamin D

While oily fish are the best food source of Vitamin D (See “Oily Fish: Your Route to Vitamin D“), several other foods supply significant amounts, including the choices below.

Look for products labeled “for bone health” or “with calcium”; these usually contain vitamin D to aid in calcium absorption.

So maximize your health by getting enough vitamin D the safe way your body will thank you!

Food	Serving Size	IUs Per Serving	Percent of Daily Requirement for People Age 51–70*
Cod liver oil	1 tbsp.	1,360	340
Vitamin D-fortified soy milk	8 oz.	Up to 120	Up to 30
Vitamin D-fortified orange juice	8 oz.	98	25
Vitamin D-fortified milk	8 oz.	98	25
Vitamin D-fortified yogurt	6 oz.	Up to 80	Up to 20
Vitamin D-fortified margarine	1 tbsp.	60	15
Vitamin D-fortified cereal	6-8 oz.	40	10
Egg yolk	1 yolk	0	0
Beef liver, cooked	3.5 oz.	15	4

* Based on a 2,000-calorie diet.

If you’re planning to eat locally caught fish, check the EPA’s fish advisories page to make sure your fish are safe to eat. www.epa.gov/waterscience/fish/states.htm

If I Wear Sunscreen, Will I Be Vitamin D-Deficient?

Arguments have been made for unprotected sun exposure because sunscreens with an SPF 8 or higher are alleged to reduce photosynthesis of vitamin D by 95 percent. Data to support this interpretation are lacking. Sunscreens allow constant permeability of a fraction of UV light equal to 1/SPF of the total, e.g. 1/15th, or 7% with SPF 15. Moreover, sunscreen users tend to apply much less than the recommended FDA amount, thus yielding far less actual protection. Incidental sun exposure – walking the dog, etc. – with effectively used SPF 15 still allows adequate vitamin D levels to be achieved, even considering the higher intake levels recently proposed.

One study of elderly patients, who generally synthesize less vitamin D from the sun due to thinning epidermis, showed that exposing just five percent of their skin surface to the sun (less than the surface area of the face and backs of the hands) yielded vitamin D levels well above deficient ranges. Such exposure would be equivalent to the incidental exposure that most humans experience daily.