Screening for vitamin D deficiency - is it worth it?
With over 90% of Americans not getting enough vitamin D in their diet, vitamin D deficiency is one of the biggest issues in nutrition today. With this in mind, the US Preventive Services Task Force (USPSTF), recently released a recommendation on screening for vitamin D deficiency, stating that there is insufficient evidence to make a conclusion. What should we take away from this report?
The goal of the USPSTF report was to answer the question: is there direct evidence that screening for vitamin D deficiency results in improved health outcomes? And upon conducting a very thorough systematic review, they found that “no study evaluated clinical outcomes or harms in persons screened versus not screened for vitamin D deficiency” – in other words, no scientists have ever asked that as a formal research question before. Is their conclusion fair? Absolutely. But is that really the only way to assess the value of screening for vitamin D deficiency?
The USPSTF report also asked the question “does treatment of vitamin D deficiency result in improved health outcomes?” While they looked at outcomes including mortality, risk of falls and fractures, In this report, they cite a number of limitations of the studies related to health outcomes variability in baseline 25(OH)D levels was on the list.
Regular readers are probably well aware that we at Talking Nutrition are very big proponents of increasing the use of nutrient status markers (i.e., the concentration of nutrients in the blood) for a variety of reasons. Chief among these reasons is that randomized controlled trials often do not account for nutrient status during recruitment, and this may explain some of the null results that have been published over the years (see here and here for additional information). Simply put, studies often recruit people who are replete for the nutrient of interest (i.e., their status is adequate or even high), and raising their status results in no additional benefit. But if they recruit people who have a low nutrient status and they bring it back to repletion through dietary intervention, benefits can be observed. In the case of the USPSTF report, few trials that were considered recruited people with inadequate vitamin D status, which makes finding conclusions difficult when faced with a such a limited data set.
So should we be screening more for vitamin D deficiency? Well, we know that inadequate vitamin D intake is the norm and not the exception. We know that nearly 1 out of 10 Americans have deficient blood concentrations of vitamin D (and that number would be even higher if you used the deficiency cutoff defined by the USPSTF!). We know that not accounting for vitamin D status in clinical trials has led to inaccurate interpretations of study results. We know that the USPSTF report – and even some interesting data released just data last month - report that vitamin D deficiency is linked to mortality in certain populations. With these facts in mind, yes, I believe that we should make measuring vitamin D status a bigger public health priority. And even if you can’t get screened, meeting your needs for vitamin D remains an effective way to maintain your health.
LeBlanc ES, Zakher B, Daeges M, et al. Screening for vitamin D deficiency: a systematic review for the US Preventive Services Task Force. Ann Intern Med 2014 (epub ahead of print).
Heaney RP. Guidelines for optimizing design and analysis of clinical studies of nutrient effects. Nutr Rev 2014; 72(1): 48-54.
Fulgoni VL 3rd, Keast DR, Bailey RL, Dwyer J. Foods, fortificants, and supplements: where do Americans get their nutrients? J Nutr 2011; 141: 1847-1854.