Does Vitamin D Supplementation Improve Lower Extremity Power and Function in Community-Dwelling Older Adults?

In more recent years, the role of vitamin D supplementation in primary care has become controversial,⁷ as observed in a recent paradigm shift of moving away from routine supplementation for fall and fracture prevention in clinical practice.⁸ In a recent meta-analysis of 33 RCTs in older community-dwelling adults, supplementation with vitamin D with or without calcium did not result in a reduction of hip fracture or total number of fractures.⁹ Moreover, the United States Preventive Services Task Force (USPSTF) recently published updated recommendations on the use of vitamin D supplementation for primary prevention of fractures¹⁰ and prevention of falls¹¹ in community-dwelling adults. In these updated recommendations, the USPSTF indicated that insufficient evidence exists to recommend vitamin D supplementation to prevent fractures in men and premenopausal women, and recommends against vitamin D supplementation for prevention of falls. Finally, USPSTF recommends against low-dose vitamin D (400 IU or less) supplementation for primary prevention of fractures in community-dwelling, postmenopausal women.¹⁰ Nevertheless, these statements are not applicable for individuals with a prior history of osteoporotic fractures, increased risk of falls, or a diagnosis of vitamin D deficiency or osteoporosis. Therefore, vitamin D supplementation for prevention of fall and fractures should be practiced with caution.

Vitamin D supplementation is no longer routinely recommended for fall and fracture prevention. However, if we believe that poor lower extremity muscle strength is a risk factor for falls,¹² then the question of whether vitamin D has a beneficial role in improving lower extremity strength in older adults needs to be addressed. Results regarding the effect of vitamin D supplementation on muscle function have so far been mixed. For example, in a randomized, double-blinded, placebo-controlled trial of 160 postmenopausal women with low vitamin D level (< 20 ng/mL), vitamin D₃ supplementation at 1000 IU/day for 9 months showed a significant increase in lower extremity muscle strength.¹³ However, in another randomized double-blinded, placebo-controlled trial of 130 men aged 65 to 90 years with low vitamin D level (< 30 ng/mL) and an SPPB score of ≤ 9 (mild-moderate limitation in mobility), daily supplementation with 4000 IU of vitamin D₃ for 9 months did not result in improved SPPB score or gait speed.¹⁴ In the study reported by Shea et al, the authors showed that 800 IU of daily vitamin D supplementation (consistent with the Institute of Medicine [IOM] recommendations for older adults¹⁵) in community-dwelling older adults with vitamin D deficiency (< 20 ng/mL) did not improve lower extremity muscle strength. This finding is significant in that it adds further evidence to support the rationale against using vitamin D supplementation for the sole purpose of improving lower extremity muscle function in older adults with vitamin D deficiency.

Valuable strengths of this study include its randomized, double-blinded, placebo-controlled trial design testing the IOM recommended dose of daily vitamin D supplementation for older adults. In addition, compared to some of the prior studies mentioned above, the study population included both males and females, although the final study population resulted in some gender bias (with male predominance). Moreover, participants were followed for a sufficient amount of time (1 year), with an excellent adherence rate (only 3 were lost to follow-up) and with corresponding improvement in vitamin D levels. Finally, the use of SPPB as a readout for primary outcome should also be commended, as this assessment is a well-validated method for measuring lower extremity function with scaled scores that predict poor outcomes.¹⁶ However, some limitations include the aforementioned predominance of male participants and Caucasian race in both intervention and control groups, as well as discrepancies between the measurement methods for serum vitamin D levels (ie, finger-stick cards versus clinical lab measurement) that may have underestimated the actual serum 25(OH)D levels.

Applications for Clinical Practice

While the null findings from the Shea and colleagues study are applicable to healthier community-dwelling older adults, they may not be generalizable to the care of more frail older patients due to their increased risks for falls and high vulnerability to adverse outcomes. Thus, further studies that account for baseline sarcopenia, frailty, and other fall-risk factors (eg, polypharmacy) are needed to better evaluate the value of vitamin D supplementation in this most vulnerable population.

— Caroline Park, MD, PhD, and Fred Ko, MD
Icahn School of Medicine at Mount Sinai, New York, NY