'D' is for Dilemma: Two Vitamin Guidelines, Two Recommendations

Best Evidence Review

Charles P. Vega, MD


January 05, 2011

In This Article

Best Evidence Reference

Hanley DA, Cranney A, Jones G, et al. Vitamin D in adult health and disease: a review and guideline statement from Osteoporosis Canada. CMAJ. 2010;182:E610-8.

This study was selected from Medscape Best Evidence, which uses the McMaster Online Rating of Evidence System. Of a possible top score of 7, this study was ranked as 5 for newsworthiness and 7 for relevance by clinicians who used this system.


Also, as a key part of this review, we have included the following:
Dietary Reference Intakes for Calcium and Vitamin D, Institute of Medicine of the National Academies. National Academic Press. Washington, DC. Available at:


Many adults are deficient in vitamin D, placing them at elevated risk for fracture. But what is the ideal way to prevent this deficiency? And does the method used matter in terms of health outcomes? Osteoporosis Canada recently reviewed these issues and offers bold new recommendations for vitamin D supplementation. But their recommendations are quite different from those offered by the Institute of Medicine.

Vitamin D is important in the prevention of disease, but the degree of benefit associated with vitamin D is a matter of debate. Although the most obvious role of vitamin D is maintenance of bone health, research has suggested that it may also be important as a means to prevent cancer and falls among older adults. Moreover, many adults lack adequate levels of vitamin D. Recognizing this significant public health issue, Osteoporosis Canada recently released its recommendations for the assessment and management of vitamin D deficiency.

Vitamin D deficiency is more common than many physicians might believe. In a clinically relevant population of postmenopausal women, the prevalence of vitamin D deficiency was as low as 1.6% among community-dwelling women to as high as 86% among institutionalized women.[1] Significant vitamin D deficiency was present in up to 76% of women with osteoporosis and 50%-70% of women with a history of fracture.

One of the challenges of reducing vitamin D deficiency across populations is determining the most appropriate source of the hormone. Most adults get the majority of their vitamin D stores from exposure to ultraviolet B radiation from the sun. This results in considerable variability in serum vitamin D levels among adults based on climate, latitude, and skin pigmentation. As a rough guide, the authors note that a young white person needs approximately 4 minutes of direct exposure to sunlight on the arms and legs to generate approximately 1000 IU of vitamin D3.

The fact that sunlight is the principal source of vitamin D creates a conflict for patients, particularly those with light skin: How to get enough sunlight to promote higher levels of vitamin D without increasing the risk for skin cancer? No clear consensus exists on this issue. One means to mitigate the potentially harmful effects of sunlight is the use of sunscreen. Although some research has suggested that sunscreen reduces the synthesis of vitamin D, a randomized trial of 113 Australian citizens found that serum levels of 25-hydroxyvitamin D3 (25-OH-D) increased by similar amounts over 1 summer whether sunscreen or a placebo was used.[2]


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