While low levels of vitamin D are linked with several diseases, ingesting too much vitamin D increases risks for other health conditions. In counseling patients on supplementation, one must take into consideration patient characteristics such as individual medical conditions and race.
Because exposure to ultraviolet light is one pathway for generating vitamin D, the question arises whether a recommendation for vitamin D supplementation should accompany advice about sun avoidance.
Guidance for counseling patients on this issue may follow the concept of “everything in moderation”, Martin A. Weinstock, M.D., Ph.D., told colleagues recently at the 74th Annual meeting of the American Academy of Dermatology in Washington D.C.
“There has been a lot of publicity in the lay press about the harms associated with not getting enough vitamin D, but there are also risks of getting too much,” says Dr. Weinstock, professor, department of dermatology, Brown University, Providence, R.I.
Adequate levels of vitamin D are important for maintaining musculoskeletal health. There have also been studies linking low levels of vitamin D to a variety of diseases, including cancer, cardiovascular disease, autoimmune disease, and infection, although that work is controversial and does not necessarily imply a causal relationship for vitamin D.
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On the other hand, it is well-documented based on outcomes of randomized controlled trials that ingestion of mega doses of vitamin D may adversely affect musculoskeletal health and the kidneys. Some data also suggest excessive vitamin D supplementation increases risks of overall mortality, cancer, and cardiovascular disease, although the evidence on those associations is not definitive, Dr. Weinstock says.
According to the Institute of Medicine, the recommended dietary allowance for vitamin D is 600 IU/day for persons up to age 70 and 800 IU/day for older individuals. These levels were developed based on the assumption of minimal sun exposure.
“Many Americans do not achieve the recommended intake of vitamin D through diet alone, and use of a vitamin supplement containing the recommended dietary allowance is probably reasonable for most people considering that 4,000 IU/day is what the Institute of Medicine recommends as the upper intake level for anyone aged 9 and older,” Dr. Weinstock said.
“Individual recommendations, however, may vary depending on medical considerations. Certain individuals may need a higher intake of vitamin D while 600 to 800 IU/day may be too much for some persons.”
The usual test for determining vitamin D sufficiency is an assay of serum 25-hydroxyvitamin D, although the test is not perfect and a low level may be misleading in some circumstances. For example, patients with sarcoidosis may have a low 25-hydroxyvitamin D level but in fact have adequate vitamin D stores. In addition, there is racial variation in 25-hydroxy vitamin D levels such that African Americans tend to have lower levels which is explained by their having lower levels of binding proteins rather than a low level of vitamin D.