Low Vitamin D Levels May Contribute to Stress Fracture Risk

Tara Haelle

December 30, 2015

At least half of patients with stress fractures who had their vitamin D levels tested had insufficient levels, according to a retrospective cohort study published in the January–February issue of the Journal of Foot & Ankle Surgery.

"An individual's vitamin D concentration is intimately linked to the absorption of dietary calcium and phosphorus," write lead author Jason R Miller, DPM, of Premier Orthopedics and Sports Medicine in Malvern, Pennsylvania, and colleagues.

They note that individuals with vitamin D deficiency only absorb approximately 10% to 15% of dietary calcium and 50% to 60% of dietary phosphorus; "thus, a decrease in bone mineralization and structural integrity can develop," with a decrease in calcium levels.

The authors also say, however, that the varying thresholds for vitamin D insufficiency are estimates among the type of patients they studied — fit, active individuals. "No minimum serum 25-hydroxyvitamin D [25(OH)D] level has been defined that can guarantee adequate skeletal health in a patient with an increased functional demand," they note.

Nevertheless, "we wish to encourage a discussion of the possibility that a higher 'norm' concentration of serum vitamin D should be recommended for active patients who may be at risk of stress fractures."

Study Confirms Previous Findings

Stress fractures, a relatively common sports-related injury, occur when stress on a bone exceeds its capacity to withstand those forces.

The researchers retrospectively reviewed the medical records of patients with confirmed stress fractures seen in Dr Miller's practice from July 2011 through August 2014. Independent review of radiographs and/or MRI confirmed the stress-fracture diagnosis in 124 patients.

The 53 patients who had their vitamin D levels measured within 3 months of their fracture diagnosis had an average serum 25(OH)D level of 31.1 ng/mL. Of these, 44 patients (83%) had levels below 40 ng/mL, considered insufficient based on standards of the Vitamin D Council. And about half, 28 patients (52.8%), had levels below 30 ng/mL, considered insufficient based on recommendations by the US Endocrine Society.

About a third (33.9%) of patients had a stress fracture in the second foot bone (metatarsal), the most common bone seen with a stress fracture, and 17.7% had one in the third metatarsal.

"The association between serum 25(OH)D levels and the occurrence of stress fractures has been previously documented in published studies, extensive investigation has been performed, and association has been reported in young and active military recruits," the authors note.

They recommend minimum serum vitamin D levels of at least 40 ng/mL to prevent stress fractures, "especially for active patients with a moderate or high functional demand."

Because 17% of patients had levels of at least 40 ng/mL, the authors describe other risk factors for stress fractures, also previously identified, including white race, female gender, nicotine and alcohol abuse, steroid use, low bone density, low body mass index, and bisphosphonate therapy.

Supplement When Vitamin D Sufficiency Accompanies Stress Fracture

When vitamin D insufficiency or deficiency exists alongside a stress fracture, the researchers recommend supplementation based largely on the Endocrine Society's guidelines for vitamin D deficient patients.

"We would advocate high-dosage supplementation for individuals with a 25(OH)D of < 35 ng/mL, introducing a 4- to 8-week regimen of a 50,000-IU weekly dose until fracture healing has occurred," they write.

"For those with a serum concentration of 35 to 40 ng/mL, we would recommend 3000 to 5000 IU daily."

After vitamin D levels are adequate, patients can take a maintenance dose of at least 2000 IU daily, they conclude.

No external funding or disclosures were reported.

J Foot Ankle Surg. 2016;55:117-120. Abstract

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