Vitamin D in Older Adults

Vitamin D deficiency is common in older adults for physiological, behavioural, and dietary reasons. It matters for two clinically important outcomes: falls and hip fractures, both of which supplementation can measurably reduce.

Why levels drop with age

1. Cutaneous 7-DHC declines ~40% between ages 20 and 80 (MacLaughlin & Holick 1985). Older skin makes less vitamin D₃ per unit UVB.
2. Less outdoor time. Reduced mobility, cognitive change, and institutional living all lower sun exposure.
3. Renal 1α-hydroxylation drops. With age and chronic kidney disease, the conversion of 25(OH)D to active calcitriol is impaired.
4. Impaired absorption. Reduced gastric acid and bile acid production, and higher rates of malabsorption disorders, reduce oral vitamin D uptake.
5. Medications. Glucocorticoids, phenytoin, and other anticonvulsants induce CYP24A1 and accelerate 25(OH)D catabolism.

Fall prevention

Falls are the leading cause of injury and injury death in adults ≥65. Meta-analyses of trials in adults ≥65 show cholecalciferol 700–1,000 IU/day reduces fall risk by ~19% (Bischoff-Ferrari 2009). The effect is mediated by improved lower-limb strength and postural control — vitamin D acts directly on muscle. Very-high-dose bolus regimens (e.g., 500,000 IU annually) have shown paradoxical increases in falls (Sanders 2010) and are not recommended.

Hip fracture prevention

Combined vitamin D (≥ 800 IU/day) plus calcium (1,000–1,200 mg/day) reduces hip fracture risk by ~15% in adults ≥65 (Bischoff-Ferrari 2012). Vitamin D alone at doses below 800 IU/day shows no benefit. The dose response is real: 400 IU/day is not enough, 800–1,000 IU/day is.

Recommended dosing after 65

• RDA: 800 IU/day (IOM 2011).
• Endocrine Society: 1,500–2,000 IU/day for adults ≥65 to maintain serum 25(OH)D ≥ 30 ng/mL.
• Test if uncertain. A single serum 25(OH)D measurement clarifies whether standard or higher dosing is needed.
• Combine with calcium 1,000–1,200 mg/day, preferably from food (dairy, greens, sardines).
• Avoid very high bolus doses. Daily or weekly is preferred over annual or 6-monthly megadoses.

Institutional and home-bound older adults

Nursing-home and long-term-care residents have the highest deficiency rates. Universal supplementation at 800–1,000 IU/day is standard-of-care in most jurisdictions and is supported by cost-effectiveness modelling — one prevented hip fracture more than pays for years of universal supplementation.