by Ruth Ann Clayton, RD

Drinking milk and spending 15 minutes in the sun everyday gives you all the vitamin D you need. Or does it?  Estimates are that 40-80% of adults are thought to be deficient in Vitamin D.  Why is it important, why such a variance in the data, and how much should we get?

Vitamin D is a hormone not a vitamin but it is so commonly called a vitamin I will use that term for this discussion. Vitamin D refers to both D2 (ergocalciferol) and D3 (cholecalciferol) forms. D2 and D3 can be found in some foods and supplements, but D3 is preferred because it is produced through the skin from sunshine. Either of these forms must be converted via the liver and kidneys into a form the body can utilize.

D is essential for life and regulates some 1,000 human genes. A deficiency can cause osteoporosis and in the extreme case, rickets.  (Remember the old cod liver oil days?  Blame rickets.)  Persons at risk for low D levels include breast-fed infants, the elderly, those with malabsorption issues, dark skinned individuals and the obese.

Yet the importance of Vitamin D goes well beyond teeth and bone development.  Without it your body is handicapped in its fight against several diseases including autoimmune disorders, diabetes, hypertension, depression, cardiovascular issues, several cancers, allergies, and asthma. It is needed for blood clotting, heartbeat regulation, thyroid function and more.

D3 is found in only a few foods naturally and in others through fortification. Natural food sources of Vitamin D3 include cod liver oil and fatty fish such as salmon, mackerel, sardines and tuna.  Small amounts are found in beef liver and egg yolks. Fortified sources include milk, cereals and orange juice. D3 is also available in supplemental form.

So where do you get sufficient amounts of this all-important vitamin?  In a perfect world your body would do the work. When your skin receives ultraviolet radiation (UVB) exposure from sunshine it triggers the production of D3 from within. Your best exposure to UVB is midday when the sun is high enough that your shadow is shorter than you.  Of course, absorption rates can vary and some individuals must avoid the sun altogether.

Therein lies the problem with the data. Generations before us worked and played extensively in the sun but now much more is done inside. Even children don’t play outside as much. Other factors, which lessen UVB exposure are fall and winter seasons, cloud cover, skin melanin, sunscreen and even car windows. But how much should we get?

In 2010 the Institute of Medicine (IOM), focusing principally on skeletal health, very conservatively increased the Dietary Allowance of Vitamin D to 400 IU for infants, 600 IU for ages 1-70 and 800 IU for those 71 and older.  The safe upper limit was set at 4,000 IU/day.  A great deal of controversy surrounds these numbers. The Council for Responsible Nutrition recommends 2,000 IU per day for adults and other experts suggest 1,000-5,000 IU or higher, depending on blood levels.

For your body to function well your vitamin D level must be maximized.  If you think you need higher amounts than recommended, talk with a medical professional. Doctors can determine your serum Vitamin D levels with a blood test.  For low blood levels consider more midday sun exposure, using supplements, and eating more fortified foods.

Ruth Ann Clayton is the Registered Dietitian at Nature’s Way.  Reach her at  This information is not intended to diagnose, treat, or cure any disease.

Ruth Ann Clayton, Registered Dietitian, is active in both the American Dietetics Association and Dietitians in Integrative and Functional Medicine Dietetic Practice Group. Her nationally accredited Dietetic Internship and her years of experience in public health and hospital settings reflect her commitment to your health and well being.

As the co-owner of Nature’s Way, she uses her comprehensive background to research products, read labels, investigate manufacturers and provide information for her customers.