Why is vitamin D status important in older adults?
- Vitamin D supplementation has been found to reduce the incidence of osteoporotic fractures in the elderly. This may occur via increased bone mineralization and/or improved muscle function and reduction in falls.
- According to the Institute of Medicine, vitamin D deficiency is defined as a serum 25-hydroxyvitamin D (25[OH]D) level < 20 ng/mL (50 nmol/L). National and international groups have suggested that a 25(OH)D level ≥ 30 ng/mL (75 nmol/L) is needed to minimize fracture and fall risk. There are insufficient data to recommend a safe upper limit of 25(OH)D.
- It has been estimated that > 40% of community-dwelling older women and men in the United States are vitamin D deficient, and the prevalence is even higher in nursing home residents.
- There are multiple causes of vitamin D deficiency in older adults, including decreased sun exposure; decreased skin synthesis; decreased intake; impaired absorption, transport, or liver hydroxylation of oral vitamin D; medications altering vitamin D metabolism (e.g., drugs that induce p450 enzymatic activity leading to decreased circulating levels of 25[OH]D); chronic illnesses associated with malabsorption; and liver and kidney diseases.
- Bone mineral density is adversely affected when serum 25(OH)D levels are < 30 ng/mL.
- Although vitamin D 3 supplementation has been found to raise serum 25(OH)D levels above 30 ng/mL, recent meta-analyses did not find that vitamin D 3 (alone or in combination with calcium) supplementation reduced fracture risk among community-dwelling older adults without known vitamin D 3 deficiency, osteoporosis or prior fracture. There is currently no evidence for antifracture efficacy of vitamin D 2 supplementation.
- Vitamin D deficiency also causes muscle weakness.
- Proximal muscle strength is linearly related to serum 25(OH)D when levels are < 30 ng/mL. Vitamin D supplementation has been associated with a 22% reduction in falls. Nursing home residents randomized to receive 800 IU/day of vitamin D 2 plus calcium had a 72% reduction in falls.
- In addition to its important role in muscle and bone metabolism, vitamin D deficiency is postulated to influence immune function, cancer risk, parathyroid hormone and renin production, and insulin secretion.
- Epidemiological studies demonstrate higher mortality in patients with insufficient or deficient levels of 25(OH)D.