I love to read what Robert Heaney writes. Professor Heaney recently applied his insightful clinical experience and extensive knowledge of vitamin D to respond to the U.S. Preventive Services Task Force’s (USPSTF) statement that there is not enough information – one way or the other – to issue a recommendation about testing for vitamin D deficiency.
First, Heaney takes the task force to task for relying on studies that are simply meaningless, at least as far as vitamin D is concerned. An example of such a study is the very large Women’s Health Initiative (designed 20 years ago, when knowledge of vitamin D was scarce), which used a dose of vitamin D that did not significantly change vitamin D levels. Why would they include a study that did not change vitamin D levels (especially such a large one) in a review or meta-analysis?
Next, he talks about biomarkers. Biomarkers are a measurable condition in an organism that provides insight into the health of that organism. Certain biomarkers change in relationship to vitamin D levels such that one can see what vitamin D level is needed to obtain maximum benefit in relation to any of these biomarkers.
The usual biomarker measured in relation to vitamin D levels is parathyroid hormone (PTH). For example, PTH is increased in vitamin D deficient individuals and generally does not fully decrease in concentration until vitamin D levels reach about 30 ng/ml. So PTH is a biomarker that says 30 ng/ml is an adequate level. However, Professor Heaney talks about another biomarker, the vitamin D content of human breast milk.
A crucial question is what circulating vitamin D blood levels does a lactating woman have to achieve so that her breast milk has adequate amounts of vitamin D? Heaney points out that research shows that 6,000 IU/day are needed to obtain adequate amounts of vitamin D in a mother’s breast milk so the suckling infant gets enough vitamin D.
Finally, Heaney draws on his clinical experience to point out logic that only a practicing physician would know. When patients know their vitamin D levels, they become very interested in obtaining “healthy levels,” whatever level the treating physician decides is healthy. Patients who do not know their 25(OH)D levels are often not interested in them, thinking that if such levels were important, their doctor would have measured them.
As Dr. Heaney concludes,
“Usually, testing improves patient adherence because it provides patient-specific, personally applicable information. General assurances that one probably needs extra vitamin D are not as compelling a motivator as knowing one’s number. Thus, whether the practitioner adheres to the widely divergent guidelines of the IOM, the Endocrine Society, or the American Geriatrics Society, measuring vitamin D status seems to be warranted, not so much to diagnose deficiency but to determine patient status relative to the selected guideline.”