ROSEMONT, Ill., April 16, 2018 /PRNewswire-USNewswire/ -- Vitamin D contributes to many important functions in the body, including the absorption of calcium and improvement of bone strength. According to a new review article published in the April 15, 2018, issue of the Journal of the American Academy of Orthopaedic Surgeons (JAAOS), vitamin D supplements help to increase muscle strength in athletes who are vitamin D deficient. Higher vitamin D levels have also been linked to reducing injury and improving athletic performance.

"Vitamin D deficiency commonly affects many people around the world," said lead study author and orthopaedic surgeon Geoffrey D. Abrams, MD. "With higher serum levels of vitamin D playing a role in muscle strength, injury prevention, and sports performance, it's essential for individuals to take necessary steps to ensure they're getting an adequate amount of vitamin D intake, whether through direct sunlight or other sources including fish, eggs, fortified dairy products, and dietary supplements. Studies also have shown that daily vitamin D supplements are proven to be more effective than weekly or monthly doses."

Vitamin D is measured using the 25-hydroxy vitamin D test using nanomoles per liter (nmol/L) or nanograms per milliliter (ng/mL). According to the Endocrine Society's clinical practice guideline for the evaluation, prevention, and treatment of vitamin D deficiency,

• less than 20 ng/mL (50 nmol/L) is deficient,
• 21 to 29 ng/mL (50 to 75 nmol/L) is insufficient, and
• 30 ng/mL (75 nmol/L) is considered a normal level.

People with very low vitamin D blood levels may be more likely to experience muscle cramps, bone pain, or joint pain. The review article authors highlight findings across several studies to determine the effect of vitamin D in three categories:

• Muscle Strength. One study examined 310 participants with an average age of 24 years. Participants had a mean vitamin D level of 12.3 ng/mL and received either vitamin D₃ or placebo supplements. Their upper and lower body strength were assessed with isokinetic dynamometers, a tool used to test the performance of different muscle groups. Results found that vitamin D supplementation in these athletes resulted in increased upper and lower body strength.
• Sports Performance. Another study investigated the effect of vitamin D on sports performance by looking at 80 American professional football players and their ability to obtain a professional contract. Seventy-seven percent of these athletes were vitamin D deficient or insufficient. The authors of that study found a statistically significant correlation between lower vitamin D levels and the athlete's release from a team due to poor performance or injury before the start of the regular season. An additional study assessed the effect of vitamin D on a group of athletes who received 5,000 International Units (IU) per day of vitamin D over an 8-week period. Seventy percent of these athletes had a vitamin D level of less than 20 ng/mL. Findings for this study showed that the group receiving vitamin D supplementation had increased vertical jump heights throughout the study, whereas the placebo group experienced no change.
• The risk of injury. Another study looked at 1,000 Royal Marine recruits in the United Kingdom to evaluate the association between vitamin D levels and risk of stress fracture. The study identified 92 stress fractures and found that recruits with vitamin D levels of less than 20 ng/mL had a 60 percent higher incidence of stress fractures than recruits with greater vitamin D concentrations.

"While vitamin D supplementation improves function and decreases fracture risk in people who are vitamin D deficient, it's important for individuals to be aware of the safe dosage amount, which varies with age and the status of an individual's current vitamin D level," explains Dr. Abrams. "We are not advocating for athletes to take additional vitamin D without first speaking with a doctor."

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Disclosures
From the Department of Orthopaedic Surgery (Dr. Abrams and Dr. Safran) and the Department of Medicine, Division of Endocrinology, Gerontology, and Metabolism (Dr. Feldman), Stanford University School of Medicine, Palo Alto, CA, and VA Palo Alto Healthcare System, Palo Alto (Dr. Abrams). J Am Acad Orthop Surg 2018;26(8):278–285 DOI: 10.5435/JAAOS-D-16-00464 Copyright 2018 by the American Academy of Orthopaedic Surgeons.

SOURCE American Academy of Orthopaedic Surgeons

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