Vitamin D: A Rapid Review

Mark A. Moyad, MD, MPH


Dermatology Nursing. 2009;21(1) 

In This Article

Why Most People Are Vitamin D Deficient

It has become difficult to identify a population of individuals that has sufficient blood levels of vitamin D. Why are so many people vitamin D deficient? A review of the various factors that can cause vitamin D deficiency are found in Table 1 (Wolpowitz & Gilchrest, 2006).

Table 1 demonstrates how easy it is to become deficient in this vitamin. For example, just getting older can reduce vitamin D levels because the mechanisms needed to synthesize its structure from cholesterol become less efficient through time, as is the case with most intrinsic synthesizing methods in the human body. It is obvious that human beings age externally (such as with wrinkles, gray hair). However, it is less obvious that humans also age internally, and inadequate vitamin D synthesis is just one example of this internal aging issue. Low levels of vitamin D are also found in individuals with larger amounts of belly fat or visceral obesity (Aasheim, Hofso, Hjelmesaeth, Birkeland, & Bohmer, 2008). Numerous theories abound as to why this is the case, such as hemodilution from greater blood volumes or the finding that adipose tissue is a greater storage site for vitamin D. Higher cholesterol levels may be associated with lower vitamin D blood levels, and conversely, cholesterol-lowering medications, such as statins, may increase vitamin D synthesis (Perez-Castrillon et al., 2008).

The lack of reliable dietary sources that contain consistently higher levels of vitamin D has been an issue. It is of interest that the highest concentration of vitamin D is found in some heart-healthy fish, so patients can get "two for the price of one" by consuming fish high in omega-3 and vitamin D, such as salmon. Fortification of some foods and beverages have not solved the vitamin D deficiency problem, and recent studies suggest that the regular intake of vitamin D may increase blood levels greater than weekly or monthly oral intakes of equivalent doses (Chel, Wijnhoven, Smit, Ooms, & Lips, 2008). Sunscreen has the ability to block ultraviolet B (UVB) light, and this form of light stimulates vitamin D synthesis in skin tissue. Thus, wearing sunscreen, and sun-protective clothing, or avoiding sunlight all have the ability to result in lower blood levels of vitamin D. However, no clinician should recommend trading one condition for another, and it is a concern that some clinicians advise regular sun exposure several times a week. Why increase a person’s risk for melanoma just to improve vitamin D levels, when supplementation is generally simplistic and cost effective? Melanoma kills, and death rates have not decreased over the last decade; the responsible recommendation lies in proper sun protection and potential vitamin D supplementation. Another thought in some medical circles is that individuals residing in areas with greater sun exposure experience higher blood levels of vitamin D. Theoretically, this makes sense; however, it has not been substantiated through recent research demonstrating low blood levels of vitamin D in individuals residing in Florida and southern Arizona (Jacobs et al., 2008; Levis et al., 2005). Perhaps regular sun avoidance, aging, and obesity are independently or synergistically involved in lowering vitamin D levels in some of these geographic areas.


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