Dr. Jacqueline Gerhart: Why Is My Vitamin D Level So Low?
Madison, Wisconsin - UW Health Family Medicine physician Jacqueline Gerhart writes a column that appears Tuesdays on madison.com and in the Wisconsin State Journal. Columns are re-published here with permission.
Dear Dr. Gerhart: I recently was told I have vitamin D deficiency and was put on prescription-strength vitamin D. Will I need to take this for life? I eat a balanced diet with plenty of fruits and vegetables. Why is my vitamin D level so low?
Dear Reader: According to the Centers for Disease Control, about one third of the U.S. population has low vitamin D. Vitamin D comes from three major sources: sunlight, food and supplementation. You likely are, unknowingly, not getting enough from these sources. Let me explain.
UV-B rays from the sun hit the skin, and this triggers vitamin D production. To get the amount of UV rays you need from the sun to make adequate vitamin D, you need 15 minutes of direct sunlight to your face, arms, shoulders, upper and lower body, three times per week. This does not include sitting inside and being exposed to sunlight through a window.
In Wisconsin, two things hinder us. First, none of us are outside in the winter in swimsuits. Second, even if we were in swimsuits, according to an article in the Wisconsin Medical Journal, our state lacks the intensity of sunlight from November through February that is needed to get enough vitamin D from the sun.
Dietary vitamin D
The good news is that our state is big on dairy, which is one main source of vitamin D. Foods like milk, cheese, butter and soy milk have vitamin D. Salmon and tuna also are high in vitamin D.
For those who are lactose intolerant or who don't like soy or fish, check out foods that are "fortified" with vitamin D. The process of fortification of vitamin D was discovered in Wisconsin. In 1923, UW-Madison biochemist Harry Steenbock showed that irradiation of foods with UV light caused rats to be cured of rickets, a bone disease from low vitamin D. He patented the process of forifying food with vitamin D, and as a result, rickets is essentially non-existent in the U.S.
But, it seems that even with fortified foods and high dairy, Wisconsin residents lack vitamin D. Recent studies show that 57 percent of postmenopausal women in Wisconsin have suboptimal vitamin D levels, putting them at high risk for osteoporosis and fractures.
The Institute of Medicine reported in 2010 that children and adults under the age of 70 should get 600 international units of vitamin D daily. Adults over 70 should get 800 IU. However, other consensus guidelines indicate that 1,000 IU per day is more appropriate for all adults.
If your vitamin D is very low, you may need "prescription strength" vitamin D, as you note in your question. Speak to your physician about your optimal vitamin D intake. The correct level for you may depend on your age, sex, ethnicity, sun exposure, medical history and current medications. These factors also determine how long you will need vitamin D supplementation. People with low calcium or low bone density may need to take this for most of their lives to prevent osteoporosis, or to slow its worsening, and to decrease fracture risk.
But instead of taking supplementation "forever" as you ask in your question, remember that you can help to improve your vitamin D levels through foods or climate. Yes, this is your doctor telling you to take a vacation to a warmer climate to destress, eat some salmon and soak up some vitamin D!
Date Published: 02/14/2012