Vitamin D Insufficiency: Is there enough evidence for clinical recommendations?

Readers of this blog over the last year, have seen many of my posts on the plethora of studies and recommendations about vitamin D. Now there’s some new data I think you’ll be interested in.While vitamin D deficiency is defined by the presence of bone disease (either rickets or osteomalacia), the term “vitamin D insufficiency” has been used to describe suboptimal blood or serum levels of vitamin D that are often associated with other skeletal and nonskeletal health outcomes. Interest in the nonskeletal effects of vitamin D dramatically over the last few years.

The physiologic interest is due to the discovery of vitamin D receptors and an enzyme (called the 1α-hydroxylase enzyme) in multiple tissues throughout the body, including cells of the pancreas, immune system, macrophages, vascular endothelium, stomach, epidermis, colon, and placenta.

However, unlike the well-established skeletal benefits of vitamin D, the evidence for other presumed effects is based mainly on observational studies or population studies.

Now, a study published in the Mayo Clinic Proceedings examines the evidence for making clinical decisions based on the strongest research to date for the potential benefits of vitamin D associated with numerous outcomes.

As I’ve discussed in past blogs, these associations include, but are not limited to, lower mortality rate; lower cardiovascular mortality; less musculoskeletal pain; and reduced risk of:

  • diabetes mellitus,
  • cancer (of various types),
  • multiple sclerosis,
  • allergy and asthma,
  • infection,
  • mental illness, and
  • renal disease.

As a result, vitamin D has become one of the hottest selling supplements in America over the last year. Here’s a report on natural medication use in the U.S. from ConsumerLab.com:

Among people who use dietary supplements, the most popular products at the end of 2010 were fish oil, multivitamins, vitamin D, calcium and CoQ10 according to a survey by ConsumerLab.com. Use of vitamin D surged in 2010 to 56.2% of those surveyed, up from 36.9% in 2008 – a 52% increase over the two-year period.  Fish oil continued its rise in popularity, used by 75% of those surveyed, (while) multivitamin use declined.

The folks who published the Mayo Proceedings article looked at ALL of the studies on vitamin D and ranked them in order of importance using this hierarchy:

  • meta-analyses of randomized controlled trials (RCTs),
  • RCTs,
  • nonrandomized intervention studies,
  • meta-analyses of observational studies (cohort and case-control studies), and
  • observational studies.

For the available RCTs, the authors reported the following data:

  • Mortality: There was a 7% lower risk of mortality in postmenopausal women who received supplemental vitamin D (meta-analysis of 18 RCTs). However, mortality assessment was not the primary aim of these trials, and trials that showed such an effect would be more likely to report this outcome, leading to potential reporting bias that could negate the findings.
  • Colorectal or breast cancer: Two separate RCTs that were part of the Women’s Health Initiative trial found no significant effect of combined supplementation with calcium and vitamin D on the risk of colorectal or breast cancer.
  • Depression: One randomized, double-blind trial showed that high-dose vitamin D (20,000 or 40,000 IU) weekly for 1 year significantly improved depression scores in overweight or obese patients vs placebo.
  • Musculoskeletal pain: Two RCTs were examined. One found no benefit of vitamin D supplementation vs placebo for reducing musculoskeletal pain (including pain due to osteoarthritis). Another double-blind RCT found that patients with vitamin D levels of 10-25 ng/mL who received high-dose vitamin D (50,000 IU) weekly for 8 weeks showed improvement on fibromyalgia scores vs placebo. So, the data are mixed.

Overall, the authors concluded that most of the current data on vitamin D is mainly based on observational, epidemiological outcomes, which are “useful for generating hypotheses but not for proving causality.”

Therefore, the evidence for benefits beyond bone health is NOT strong. However, the data for positive effect is there, and the data for harm in minimal.

So, here’s my current protocol:

  • Offer a 25-hydroxy vitamin D (25OH vit D) blood test for all patients during their preventive medicine exams.
  • If the 25OH vit D level is below 30, the patient may either:
  • 1) Take a prescription tablet containing 50,000 IU of vitamin D2 weekly for 12 weeks, or
  • 2) Take 2000 IU of over-the-counter vitamin D3 daily for 12 weeks,
  • Then recheck the level, aiming for a level above 30.

 

 

Reference

Thacher TD, Clarke BL. Vitamin D insufficiency. Mayo Clin Proc. 2011;86(1):50-60.

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