How Does Vitamin D Affect Bone Health and Fracture Risk in Older Adults?

The short answer

Vitamin D is essential for calcium absorption in the gut — without adequate vitamin D, the body absorbs only 10–15% of dietary calcium, compared to 30–40% with sufficient vitamin D. Deficiency leads to secondary hyperparathyroidism, bone resorption, and increased fracture risk. Supplementation reduces fracture risk by 20–30% in deficient older adults when combined with calcium.

What the evidence actually shows

A 2005 meta-analysis by Bischoff-Ferrari et al. in JAMA, pooling 7 RCTs, found that vitamin D supplementation (700–800 IU/day) reduced hip fracture risk by 26% and any non-vertebral fracture risk by 23% in older adults. A 2010 individual patient data meta-analysis by the DIPART Group, pooling 68,500 patients from 11 RCTs, found that combined vitamin D and calcium supplementation reduced total fracture risk by 8% and hip fracture risk by 16%. The benefits were most pronounced in institutionalised older adults with baseline deficiency. Holick (2007) established that vitamin D deficiency (serum 25-hydroxyvitamin D below 20 ng/mL) is extremely common in older adults, affecting 40–60% of those over 65 in northern latitudes.

"Vitamin D supplementation of 700–800 IU/day reduced hip fracture risk by 26% in older adults."

— Bischoff-Ferrari et al., JAMA 2005

What the major health authorities say

MedlinePlus and the NIH Office of Dietary Supplements recommend 600 IU of vitamin D per day for adults aged 19–70, and 800 IU for those aged 71 and older. The NIA notes that older adults, people with dark skin, and those who spend little time outdoors are at particular risk of deficiency. Testing serum 25-hydroxyvitamin D levels is recommended for at-risk individuals. The NIH notes that vitamin D is fat-soluble and is better absorbed when taken with a meal containing fat.

Practical implications

For adults over 65, particularly those with limited sun exposure, supplementing with 800–1,000 IU of vitamin D3 per day is a reasonable precaution. Testing serum 25-hydroxyvitamin D is the most accurate way to determine whether supplementation is needed — a level below 20 ng/mL indicates deficiency, and levels of 30–50 ng/mL are considered optimal for bone health. Vitamin D3 (cholecalciferol) raises serum levels more effectively than D2 (ergocalciferol). Calcium intake should also be adequate (1,000–1,200 mg/day from food and supplements combined) for maximum bone benefit.

Where reasonable people still disagree

• The optimal serum 25-hydroxyvitamin D target for bone health and overall longevity — whether 30 ng/mL or 50 ng/mL is the appropriate goal.
• Whether vitamin D supplementation provides meaningful fracture risk reduction in individuals who are not deficient at baseline.
• The cardiovascular and cancer prevention benefits of vitamin D supplementation, which remain contested despite promising observational data.