For at least a decade, I have been touting to the importance of vitamin D. When I received my Master of Science degree in human nutrition from the University of New Haven in Connecticut in 1996, I carried with me some ideas and hypotheses that were considered well outside the mainstream of conventional scientific thinking at the time. I was convinced that the role vitamin D played in bone health was but the tip of an iceberg. Vitamin D’s depth and complexity was yet to be explored or understood. As a novice in the burgeoning field of ‘nutrition’, it was a challenge to be taken seriously. In the eyes of conventional medicine, nutrition has long been viewed a ‘soft science’ worthy of just a couple of hours of course work (perhaps only an elective). In addition, I was just starting out.
I began taking a vitamin D supplement of 1,000 IUs per day in 2001 in addition to the 800 IUs I was getting in a multivitamin. My primary care physician tested my own serum levels of vitamin D for the first in 2007. I was surprised to learn that in spite of what many would consider high doses of vitamin D, my serum levels of D had not reach the ‘sufficiency’ state.
In the last decade there has been increasing awareness concerning the widespread role of vitamin D in health and disease. It seems almost every week there is some new positive information about the health benefits of sufficient levels of vitamin D. The scientific and medical communities have finally recognized that vitamin D is not just important in bone and skeletal health. Vitamin D plays a role in a wide range of metabolic and cellular functions. In addition to preventing childhood rickets, adult osteomalacia, muscle weakness and osteoporosis, optimal levels of vitamin D play a role in preventing autoimmune diseases, cardiovascular diseases, deadly cancers, type II diabetes, infectious diseases and neurological disorders. And yet, more the half the world’s population has a vitamin D insufficiency.
History of vitamin D
By definition a vitamin is an essential biological compound that cannot be synthesized in the body and must be consumed in the diet. In the 1920’s a substance found in cod liver oil (separate from vitamin A) was identified as the ‘antirachetic’ factor that cured the bone deforming disease rickets. At that time this factor was named vitamin D. Later it was established a ‘pre-vitamin D’ compound is synthesized in the skin upon exposure to ultraviolet light. That compound is transformed in the kidneys and liver to active vitamin D. Vitamin D’s role in calcium and phosphorous metabolism is well known. However vitamin D receptors have been found in every tissue and cell in the body including immune, brain, colon, prostate, and breast cells, among many others making it clear vitamin D has global hormonal activities. Ensuring optimal vitamin D levels will contribute to the reduction and frequency of so many chronic diseases and illnesses it is high time we reevaluate the Dietary Reference Intake (RDI) for vitamin D and redefine the sufficiency range for serum 25-hydroxyvitamin D (25[OH]D).
RDI for Vitamin D
Just to keep us on our toes, the USDA has changed the terminology used to establish the recommended dietary intake again. We’ve gone from RDAs (recommended allowances), to RDIs (intakes) and now to Dietary Reference Intakes (DRI)s. Registered Dieticians and some medical professionals are fond of saying “if one eats a variety of healthy foods, including fruits, vegetables, dairy products, meats, poultry and fish you will get all the vitamins and minerals one needs.” Few would suggest this is possible in the case of vitamin D. The only naturals food sources of vitamin D consist of oily fish, cod liver oil, and mushrooms exposed to sunlight or UV light. Dairy products in the US are commonly fortified with vitamin D. Last year the Institute of Medicine appointed a panel to review RDIs for vitamin D and calcium. That panel raised the DRI for vitamin D from 400 IUs to 600 IUs and the tolerable upper limit of intake from 2,000 IUs to 4,000 IUs. Few scientists agree with this miniscule increase in the recommended intake. The best way to ensure sufficient levels of vitamin D is to expose one’s skin to the sun without the interference of sunscreen. However, sun exposure is no longer considered a reliable or safe way to maintain sufficient levels of vitamin D.
Successful conversion of vitamin D in the skin depends upon one’s age, skin color, and one’s proximity to the equator. It also requires going out in fairly strong sunshine without the protection of sunscreen (which may increase the risk of skin cancer). Walter Willett, MD, MPH, principal researcher of the very large population based NHANES (National Health and Nutrition Examination Study) points out that the IOM’s recommendations are not high enough to reach the optimal level for bone health and fall and fracture risk reduction.
Serum 25(OH)D levels
Vitamin D status can be accurately and inexpensively determined by a simple blood test: 25 hydroxy-vitamin D [25(OH)D]. It has been suggested that a vitamin D deficiency occurs at less than 20 ng/mL and a vitamin D insufficiency is 21-29 ng/mL. These represent the levels required for effective calcium metabolism and maintenance of bone and skeletal health. There is evidence that higher serum levels are required to get the non-skeletal benefits of vitamin D. Women with blood levels of about 48 ng/mL had a 50% reduction in breast cancer risk. Healthy adults living in Boston, MA received 1,000 IUs of vitamin D a day for 3 months during the winter. At the outset of the experiment the average 25(OH)D level was 18 ng/mL. By the end of the treatment period, the average 25(OH)D level rose to 28ng/mL and therefore did not achieve a vitamin D sufficiency. One of the most effective ways to quickly achieve a vitamin D sufficiency state is to administer vitamin D2 in a pharmacologic dose of 50,000 IUs once a week for 8 weeks. This is the equivalent of giving approximately 6,000 IUs per day. To maintain this sufficiency state, the 50,000 IUs should be continued every other week indefinitely.
Vitamin D Toxicity
The occurrence of vitamin D toxicity is extremely rare. Too much vitamin D can result in excess calcium in the blood or urine which increases the risk of developing kidney stones. A vitamin D toxicity is easily reversed upon discontinuation of the vitamin.
The fact that there is a widespread vitamin D deficiency and insufficiency is far more concerning. A simple blood test enables us to determine a vitamin D deficiency and insufficiency. The global consequences of a vitamin D insufficiency have profound implications. Anthony Norman, PhD, an international expert in vitamin D, suggests there should be a major policy change regarding people’s vitamin D intake because achieving sufficient levels will reduce the frequency of so many diseases including childhood rickets, adult osteomalacia, cancer, autoimmune disease, hypertension, cardiovascular disease, and obesity. “A reduction in the frequency of these diseases would increase the quality and longevity of life and significantly reduce the cost of medical care worldwide.”
Holick MF. Vitamin D: evolutionary, physiological and health perspectives. Curr Drug Targets. 2011 Jan:12;(1):4-18
Holick MF. The Vitamin D Deficiency Pandemic: a Forgotten Hormone Important for Health. Public Health Reviews. 2010 Vol. 32, No 1, 267-283
 Garland CF, Gorham ED, Mohr SB, Grant WB, Giovannucci EL, Lipkin M, et al. Vitamin D and prevention of breast cancer: pooled analysis. J Steroid Biochem Mol Biol. 2007;103:708-711.
 Holick MF, Biancuzzo RM, Chen TC, Klein EK, Young A, Bibuld D, et al. Vitamin D2 is as effective as vitamin D in maintaining circulating concentrations of 25-hydroxyvitaminD. J Clin Endocrinol Metabol 2008;93:677-81.
 Holick MF. The Vitamin D deficiency pandemic: a forgotten hormone important for health. Publ Health Rev.2010; Vol 32. (1).267-283