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Because of the high risk of vitamin D deficiency and insufficiency among bariatric surgery patients, both referring physicians and bariatric specialists need to take a greater role in personalizing vitamin D supplementation regimens in these patients. Most referring physicians aren't aware of the importance of early vitamin D intervention or may not be addressing the issue in the most effective manner. And even with the latest medical research, doctors specializing in bariatric surgery do not yet know the best vitamin D supplementation regimen for these patients. As a result, the referring physicians and bariatric specialists should be working together to closely monitor and tailor an individualized supplement regimen for each patient.

Traditionally, vitamin D deficiency after bariatric surgery was thought to be entirely due to side effects of the procedure, such as poor absorption of fat-soluble nutrients. But, now it appears that , with as many as 98% of bariatric surgery candidates having either vitamin D deficiency or insufficiency. Malnutrition persists after surgery despite supplementation and weight loss (which theoretically releases vitamin D stored in the fat).

The primary concern over vitamin D deficiency is that when these patients may be less able to absorb vitamin D, and, thus, treatment prior to surgery may be more effective. Improving vitamin D status prior to surgery may also improve healing and shorten the length of stay in the hospital following bariatric surgery.

What is an optimized vitamin D level in a patient prior to or following bariatric surgery? According to the , physicians should bring blood concentrations to greater than 30 ng/mL of 25-hydroxyvitamin D, the circulating form of vitamin D. The society recommends achieving these readings by delivering the standard daily dose of at least 3,000 IU, test the patient's blood, adjust the dose, test again and repeat until the patient's vitamin D readings are optimized. A physician may consider giving high doses of vitamin D -- 50,000 IU one to three times weekly or even daily -- if necessary for patients following surgery. The recommendations from the society sound like a ringing endorsement for personalized medicine.

A key consideration in vitamin D supplementation that physicians need to be aware of is the form of vitamin D given. Vitamin D3 is made in the skin during sun exposure and is found in over-the-counter supplements, whereas vitamin D2 is uncommon in the diet and found in high-dose prescription vitamin D supplements. In a meta-analysis of 57 studies, patients given vitamin D3 had an 8.08-ng/mL larger improvement in 25(OH)D readings over the same dose of vitamin D2 -- meaning vitamin D3 proved more effective. Despite this, many doctors inadvertently prescribe vitamin D2 to their bariatric surgery patients. Many doctors do not realize that writing a prescription for vitamin D will likely yield vitamin D2, and many also do not know the difference in effectiveness between these two forms. I recently showed that 87% of our bariatric surgery candidates prescribed high-dose vitamin D were given vitamin D2, despite that many patients only get a short window for preoperative treatment.

As for the appropriate dosing regimen, of 25 separate studies testing different regimens, reported consistently optimized vitamin D readings in patients. These studies ranged from a daily multivitamin to high doses of vitamin D (50,000 IU monthly or weekly) and various combinations of daily and high doses. These findings from my recent review echo the society's recommendations, yet no studies giving dosages up to 5,000 IU daily reached optimized vitamin D readings universally. However, some patients did reach blood concentrations over the recommended 30 ng/mL. Would the best course of treatment really be to increase the standard dose for all, or should we only increase the dosage for those patients who are still below the recommended concentration?

Only one of the 25 studies piloted a semipersonalized approach. In that study, the physicians used a four-tiered design where all patients received a dose of at least 800 IU of vitamin D3 daily, and received increasing amounts depending on their initial vitamin D readings. This semipersonalized approach appeared safe and effective, but it did not universally produce optimized vitamin D readings, which climbed as high as 87 ng/mL in one patient. While no adverse events occurred in this study, two patients had mild hypercalcemia (elevated blood calcium), and two had hypercalciuria (elevated urine calcium). Thus, this protocol undertreated some patients and overtreated others.

There may be several reasons why this semipersonalized approach didn't work as expected, and why strict personalization may be required for this patient population. For instance, the tiers might need to cover smaller concentration ranges to properly treat all patients in each tier.

Also, 90% of an individual's vitamin D comes from sun exposure, so the season in which the vitamin D testing occurred could have skewed the assessment of status too low in winter (least sun) or too high in summer (most sun).

Plus, individuals appear to react differently to identical doses of vitamin D. The fact that individuals have different reactions to the same dose is becoming clearer and likely has multiple causes. , which affect the amount of free vitamin D -- that which is available for the body to use.

Additionally, a larger response is seen in individuals who are given supplements with moderate vitamin D readings than in those with low or high readings.

The on vitamin D levels is another reason to argue for personalized treatment, as the dose could be optimized for the time when vitamin D is lowest in the body, in January to March (or even early April).

The best method of treating vitamin D malnutrition pre- and post-bariatric surgery is to deliver a higher daily dose of vitamin D and then adjust to the appropriate blood 25(OH)D readings, which will require personalized medicine and treatment from both referring physicians and bariatric specialists. Personalized vitamin D supplementation will prevent both under- and overtreatment in bariatric surgery patients and is likely also important for many other patient populations who are at risk for vitamin D deficiency, including people who have obesity or in those who are overweight.

, is a postdoctoral fellow in the Department of Surgery at the Johns Hopkins University School of Medicine, where she studies the effect of nutrition on surgical outcomes as part of the Johns Hopkins Center for Bariatric Surgery. Follow her on Twitter or Facebook at .

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