By TEDDY JONES, R.N., C.S., Ph.D., Family Nurse Practitioner

Three of my recent journals contained articles on vitamin D, which we probably are all familiar with as the “sunshine vitamin.”

The articles suggested many of us might have insufficient amounts of active vitamin D. I looked further into the research behind those articles.

Here’s what I found.

Vitamin D is necessary for proper utilization of calcium in the body and is, therefore, essential for healthy bones.

It also is thought to be a factor in the function of the immune system, muscle strength and possibly some autoimmune diseases.

Humans acquire vitamin D either through sun exposure, food containing vitamin D, or use of supplements.

Vitamin D from food must be converted by chemical processes in the body to become its active form, vitamin D3, which is created by skin tissue upon exposure to sunlight. Supplements are either vitamin D2 or D3.

Vitamin D also is deposited in fat, which is not readily available for use.

Nutritionists are developing new recommendations in May for daily vitamin D requirements. That’s just after this column was written, but the new recommendations were expected to be for greater amounts than earlier, based on newer research.

A deficiency of vitamin D causes rickets and other poor bone development in children, muscle weakness and pain in adults, and osteomalacia (soft bones prone to fracture).

Insufficiency (less than desirable amounts, but not at the level of deficiency) may be a factor in a number of health problems under study, such as increased risk of some types of cancer and autoimmune diseases, elevated blood pressure, and diabetes.

Key Points

• Vitamin D is vital for the growth and health of children and adults.

• Daily vitamin D requirements increase with age after age 50.

• Sun exposure, foods and supplements are sources of vitamin D.

Farmers and ranchers

You might think that as a farmer or rancher you receive enough sun exposure to take care of your vitamin D needs, particularly if you live where the sun shines a lot.

Well, it all depends.

Some of us have a greater likelihood than others to have insufficient, or deficient, amounts of vitamin D. For example, the skin of older people does not “manufacture” as much vitamin D from sun exposure as those who are younger.

Those who are housebound or who seldom remain in the sun when they leave home may not get sufficient exposure. Darker skinned people synthesize less vitamin D than those with light colored skin. People who are obese have less of their vitamin D available for use than those of normal weight.

Those who take medications that limit fat absorption (cholestyramine, for example), or take medications that interact and decrease vitamin D levels (phenytoin, carbamazepine, Phenobarbital, for example) may lack the vitamin. People who have gastric bypass surgery do not absorb the fat in which vitamin D is available in foods.

Current recommendations for daily vitamin D for people who do not have conditions affecting vitamin D metabolism are 200 international units, or IU, for infants and children to 18 years; 200 IU for adults 19 to 50; 400 IU if 51 to 70; and 600 IU if 71 and older.

Who should take it?

Should everyone take a vitamin D supplement daily?

No, not everyone, and not anyone who doesn’t seek the advice of their health care provider. Why?

Two reasons: The first is that it is possible to reach toxic levels from taking too large a continuing dose of supplemental vitamin D; the second is many people can assure sufficient vitamin D by eating vitamin D-containing foods and by selective exposure to sunlight.

You’ve been advised, and rightly so, that too much sun exposure can increase the risk of skin cancer. It won’t require too much sun to get enough vitamin D. Five to 30 minutes of exposure between 10 a.m. and 3 p.m. twice weekly to skin not covered with sunscreen will provide an adequate weekly “dose” of sunshine for normal people.

The UVB rays are necessary to convert the chemical in the skin to vitamin D, so exposure through glass doesn’t count because UVB rays don’t penetrate glass.

But if you have any of the factors mentioned above, or are at an age requiring the higher intakes daily, it’s important to include foods containing vitamin D in your daily diet.

Good sources of vitamin D

Common foods that would do the trick for supplying vitamin D are:

• vitamin D fortified milk, 8 ounces, 98 IU

• salmon, canned, 3 ounces, 530 IU

• vitamin D fortified soy milk, 8 ounces, 100 IU

• canned sardines, 3 ounces, 231 IU

• vitamin D fortified orange juice, 8 ounces, 100 IU

• vitamin D fortified breakfast cereal, 1 cup, 40 to 50 IU

Because of symptoms of risk factors mentioned or you have skin cancer, if you wonder if you need supplementation, ask your health care provider.

The level can be measured with a blood test, and if you need a supplement, you can choose one with your provider’s guidance.

For more information on vitamin D, go online to ods.od.nih.gov/factsheets/VitaminD_pf.asp.

Jones is professor emeritus in the School of Nursing, Texas Tech Health Sciences Center, at Lubbock.

This article published in the June, 2010 edition of THE FARMER-STOCKMAN.

All rights reserved. Copyright Farm Progress Cos. 2010.