The Sunshine Vitamin and Health: Optimal Vitamin D Levels

By Russell H. Greenfield, MD, Dr. Greenfield is Clinical Assistant Professor, School of Medicine, University of North Carolina, Chapel Hill, NC, and Visiting Assistant Professor, University of Arizona, College of Medicine, Tucson, AZ; he reports no consultant, stockholder, speaker's bureau, research, or other financial relationships with companies having ties to this field of study.

Source: Bischoff-Ferrari HA, et al. Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr 2006;84:18-28. Erratum in: Am J Clin Nutr 2006;84:1253; dosage error in abstract.

Abstract: In an attempt to quantify the optimal level of 25-hydroxyvitamin D [25-(OH)D] needed to enhance health, a rigorous literature review was performed. The common definition of an optimal 25(OH)D serum concentration is generally regarded as that which maximally suppresses parathyroid hormone (PTH, which promotes bone loss), but estimates in this regard vary widely as PTH levels fluctuate with time of day, diet, physical activity, and renal function. In this paper, results from randomized controlled studies, dose-response trials, and prospective and epidemiologic data were summarized for the effect of a given level of 25(OH)D on multiple health endpoints other than PTH suppression or optimal calcium absorption, including bone mineral density, anti-fracture efficacy, lower extremity function, falls, dental health, and prevention of colorectal cancer. For all examined endpoints, optimal 25(OH)D serum concentrations started at 75 nmol/L (30 ng/mL), but the best outcomes were found with serum levels that ranged from 90 to 100 nmol/L (36-40 ng/mL). The current recommended daily intake of vitamin D depends upon age and ranges from 200 to 600 IU/d; unfortunately, optimal 25(OH)D levels cannot be attained in most people with the present suggested levels of intake. Thus, an increase in the currently recommended daily intake of vitamin D to more than 1,000 IU (40 mg) seems warranted for all ethnic and racial groups.

Comments: Results of literature reviews do not typically merit a change in therapy, but this well-done paper does just that. A seeming explosion in the amount of data pointing toward a previously under-recognized importance of optimal vitamin D levels for health has been taking place. Potential benefits have been identified with the endpoints used in the article, but study results also suggest benefits of optimal 25(OH)D levels in the setting of other maladies such as multiple sclerosis, hypertension, tuberculosis, insulin resistance, osteoarthritis, and for chemoprevention against additional cancers. The majority of people in the United States have 25(OH)D serum levels significantly below the 90-100 nmol/L (36-40 ng/mL) optimum established by this review, especially the elderly. Baseline 25(OH)D levels can vary with latitude and degree of food fortification, but most all people will be relatively vitamin D-deficient during the cold winter months. Concerns continue to exist with respect to sun exposure and skin cancer risk, but data on proper dietary intake and use of supplemental vitamin D are strongly suggestive of health benefit. With regard to supplemental vitamin D, cholecalciferol (D3) is a more efficient agent than is ergocalciferol (D2), though the latter is not harmful. The results summarized in this article consistently point to the need for a vitamin D intake of more than 700-800 IU/d. Many experts now point to a safe maximal daily intake of 2,000 IU vitamin D. Of note are data showing that intakes of 4,000-10,000 IU/d are safe for young adults, and that hypercalcemia develops in most people only with serum 25(OH)D concentrations higher than 220 nmol/L. This literature review did not address optimal vitamin D intake for children.

Conclusion: Our conservative nature as practitioners typically gives us pause when considering a significant increase in the recommended dosage for any agent, let alone a fat-soluble vitamin like vitamin D; however, the sheer volume of data suggesting benefit of optimal 25(OH)D levels for the prevention and, in some instances, treatment of disease is compelling. Considering that the vast majority of people do not have adequate intake of vitamin D to attain levels of 25(OH)D that appear to enhance health, and with a gradually expanding safe therapeutic range, it appears clear that practitioners should be recommending higher levels of vitamin D intake. This is a paper you might consider making hard copies of and sharing with your colleagues.