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Higher Vitamin D Levels Associated With Improved Lower Extremity
Function

Yael Waknine

Aug. 31, 2004 — Serum 25-hydroxyvitamin D (25[OH]D) concentrations
higher than 40 nmol/L are associated with improved lower extremity
function in ambulatory patients aged 60 years and older, regardless of
activity level, ***, age, race or ethnicity, and calcium intake,
according to the results of a population-based survey published in the
September issue of the American Journal of Clinical Nutrition.

"The protective effect of vitamin D on fractures has been attributed
to the established moderate benefit of vitamin D for calcium
homeostasis and bone mineral density," writes Heike A.
Bischoff-Ferrari, MD, from the Robert B. Brigham Arthritis and
Musculoskeletal Diseases Clinical Research Center at Brigham and
Women's Hospital in Boston, Massachusetts, and colleagues.

"However, an alternative explanation might be that vitamin D affects
factors directly related to muscle strength and function, thus
reducing fracture risk through fall prevention, in addition to its
benefits on calcium homeostasis."

The investigators explored the relationship between vitamin D levels
and muscle strength and function in 4,100 subjects aged 60 to more
than 90 years (mean age, 71.4 ± 7.9 years; 49% women). Serum
concentrations of 25(OH)D were measured in all subjects by
radioimmunoassay.

Lower extremity function was assessed using the timed eight-foot walk
test and the repeated sit-to-stand test. Decreased performance time
was associated with increased lower extremity functionality.

Subjects classified as active (75%) had walked one mile without
stopping, swam, jogged, bicycled, danced, exercised, or gardened in
the previous month. Inactive subjects (25%) had not.

After controlling for activity level (active or inactive), ***, age,
race or ethnicity, and calcium intake, regression ****ysis showed that
subjects in the highest 25(OH)D quintile had a mean 5% decrease in
time of 0.27 seconds in the eight-foot walk test compared with those
in the lowest quintile of 25(OH)D concentration (95% confidence
interval [CI], -0.44 s to -0.09 s; P < .001).

In addition, subjects in the highest 25(OH)D quintile had a mean 3.9%
decrease of 0.67 seconds in the sit-to-stand test compared with those
in the lowest quintile (95% CI, -1.11s to -0.23 s; P = .017).

25(OH)D concentration was positively associated with improved lower
extremity function throughout the reference range (22.5 - 94.0
nmol/L), with most of the improvement occurring at levels between 22.5
and ~ 40.0 nmol/L. Further improvement of less magnitude continued in
the 40.0 to 94.0 nmol/L range.

"[i]n both active and inactive ambulatory U.S. women and children aged

musculoskeletal function in the lower extremities," the authors write,
noting that while concentrations of 40 nmol/L or greater are desirable
for optimal function, concentrations as high as 100 nmol/L appear
advantageous.

"Given the high prevalence of low 25(OH)D concentrations and
inactivity in this national survey and the positive association
between 25(OH)D and lower-extremity function, vitamin D
supplementation may offer a way to improve lower-extremity function in
both active and inactive subjects aged >/= 60 y," the authors
conclude.

The study was supported by the Harvard Hartford Foundation, the
Kirkland Scholar Award, the Irene and Fredrick State Nutrition
Education Fund, the Swiss Foundation for Nutrition Research, and the
International Foundation for the Promotion of Nutrition Research and
Nutrition Education.

Am J Clin Nutr. 2004;80:752-758

Reviewed by Gary D. Vogin, MD

Vitamin D Supplementation and Fracture Prevention
Clinical Articles

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Performance, and Falls in Older Persons: A Systematic Review

http://www.medscape.com/viewarticle/488280?src=mp