According to the world?s foremost medical expert on calcium and vitamin D, Professor Heaney (also see bio below), of all the nutrients associated with chronic disease, none have the potential payoff of vitamin D. Dr. Heaney says that 25-hydroxyvitamin D (calcidiol) levels below 32 ng/ml constitute vitamin D deficiency. In 2003 he discovered that normal humans utilize about 10 times the RDA of 400 IU a day. So we need about 4,000 IU, not 400, of vitamin D a day, which suggests that vitamin D deficiency in the United States (and much of the world) is common, not the exception. Even the nation?s premier hospital, Massachusetts General, is seriously afflicted--85 percent of their patients were found to be vitamin D deficient.
Only relatively recently has reliable measurement of vitamin D been available, and most of the physiology of vitamin D had been worked out before that time and thus was unconnected to specific levels of vitamin D supplementation. For example, although the Food and Nutrition Board had no difficulty in identifying 25(OH)D as the functional indicator for vitamin D status, they were not able, with the data that existed at that time, to assign numerical values to the lower limit of the normal range or to assign cutoff values for various vitamin D activities.
As a result, current measurements are usually related to laboratory "reference" ranges. This is inevitably a circular argument inasmuch as such ranges record what is observed in people who are considered "normal" only because they do not have recognizable rickets or osteomalacia. The evidence is also irrefutable that vitamin D costs just pennies a day. It is important to know that for most of you, cod liver oil is NOT sufficient. While it will certainly help, I find most of my patients, well over half, require additional vitamin D supplementation beyond cod liver oil. Some require as much as 10,000 units per day for one to two months. At this dose it is important to monitor vitamin D blood levels to prevent any toxicity from vitamin D overdosing.
Robert P. Heaney, M.D., F.A.C.P., F.A.C.N., is a John A. Creighton University Professor of Medicine, Department of Medicine of Creighton University has published more than 300 original papers, chapters, monographs, and reviews in scientific journals. He is a frequently invited editorial writer for the major medical journals, including JAMA, Annals of Internal Medicine, American Journal of Clinical Nutrition and the Journal of Clinical Endocrinology and Metabolism. He serves on numerous nutrition and scientific advisory panels. Dr. Heaney was a member of the 1997 Institute of Medicine?s Food and Nutrition Board involved in the development of recommendations for both calcium and vitamin D nutrition.
American Journal of Clinical Nutrition November 2003 Vol. 78, No. 5, 912-919,