25(OH) vitamin D and functional outcomes in older adults admitted to rehabilitation units: the safari study

Abstract

Vitamin D (25(OH)D) deficiency is associated with poor physical performance; little is known about its impact on geriatric rehabilitation. We found a positive non-linear relationship between 25(OH)D and functional gain, stronger in levels < 16 ng/ml (below the cutoff for "deficiency"). An early 25(OH)D dosage may be advisable for this population.

Introduction: Vitamin D (25(OH)D) deficiency is highly prevalent in older people, and it is associated with poor muscular strength and physical performance. Its impact on functional outcomes during geriatric rehabilitation has been poorly studied. We aim to analyze the association between 25(OH)D and functional recovery in geriatric rehabilitation units.

Methods: We conducted a prospective multi-center cohort study including patients ≥ 65 years old admitted to 3 geriatric rehabilitation units in Italy and Spain, after orthopedic events or stroke. Outcomes were absolute functional gain (AFG, discharge-admission Barthel index) and ability to walk (AW) at 3 months after admission. The association between 25(OH)D quartiles (Q1-Q2-Q3-Q4) and outcomes was explored using linear or logistic regression models.

Results: We included 420 patients (mean age = 81.2 years [SD = 7.7], 66.4% females, mean 25(OH)D concentration = 13.5 ng/ml [SD = 8.7]) (to convert to nmol/l multiply by 2.496). A non-linear relationship between 25(OH)D and AFG was found, with a stronger association for 25(OH)D levels < 16 ng/ml. Compared to Q1 (25(OH)D ≤ 6 ng/ml), participants in Q3 (25(OH)D 11.5-18.2 ng/ml) had the best AFG and AW (mean AFG [SD], Q1 = 28.9 [27.8], Q2 = 32.5 [23.5], Q3 = 43.1 [21.9], Q4 = 34.5 [29.3], R² = 7.3%; AW, Q1-Q2 = 80%, Q3 = 91%, Q4 = 86%). Regression models adjusted for potential confounders confirmed these results (AGF Q2, β = 2.614, p = 0.49; Q3, β = 9.723, p < 0.01; Q4, β = 4.406, p = 0.22; AW Q2, OR [95% CI] = 1.84 [0.67-5.33]; Q3, OR [95% CI] = 4.01 [1.35-13.48]; Q4, OR [95% CI] = 2.18 [0.81-6.21]).

Conclusions: In our study, 25(OH)D concentration showed a positive association with functional outcomes at 3 months. The association is stronger below the usual cutoff for "deficiency." Dosage of 25(OH)D concentration may help identify geriatric rehabilitation patients at risk for a worse functional recovery.

Keywords: Aged; Barthel index; Functional recovery; Rehabilitation; Vitamin D.