Based on the results of a pooled analysis of 11 unrelated randomized clinical trials investigating vitamin D supplementation and fracture risk in more than 31,000 older adults, Bess Dawson-Hughes, MD, director of the Bone Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging (USDA HNRCA) at Tufts University, says higher doses of Vitamin D may be the most beneficial in reducing bone fractures in this age group.

As part of the study, published today in The New England Journal of Medicine, Dawson-Hughes and colleagues divided the subjects into quartiles ranging from 0 to 2,000 International Units (IUs) of daily vitamin D intake. In the top quartile, there was a 30% reduction in hip fracture risk and a 14% reduced risk of fracturing other bones, compared to the control groups.

"Taking between 800 IUs and 2,000 IUs of vitamin D per day significantly reduced the risk of most fractures, including hip, wrist and forearm in both men and women age 65 and older," said Dawson-Hughes, the study's senior author. "Importantly, we saw there was no benefit to taking Vitamin D supplements in doses below 800 IUs per day for fracture prevention."

Dawson-Hughes and colleagues analyzed each participant's vitamin D supplementation within and independent of the study protocol, controlling for age, vitamin D blood levels at baseline, additional calcium supplementation and whether the person lived independently or under medical care.

"Evaluation of individual-level data is the gold-standard of meta-analysis," said lead author Heike Bischoff-Ferrari, MD, D.Ph., director of the Centre on Aging and Mobility at the University of Zurich and Waid City Hospital and a visiting scientist in the Bone Metabolism Laboratory at the USDA HNRCA. "Our results make a compelling contribution to the existing data on Vitamin D and fracture risk in men and women age 65 and older, whose vulnerability to bone density loss and osteoporosis leave them prone to fractures resulting from thinning bones."

The current Dietary Reference Intake (DRI) for vitamin D in older adults set by the Institute of Medicine (IOM) is a minimum of 600 IUs per day for adults between 51 and 70 years-old and 800 IUs in adults over 70.

"Vitamin D supplementation is an efficient intervention for a costly injury that affects thousands of older adults each year," said Dawson-Hughes, who is also a professor at Tufts University School of Medicine. "The average recovery is long and painful and deeply impacts quality of life. After a fracture, older patients may only regain partial mobility, resulting in a loss of independence that is personally demoralizing and that can place added stress on family members and caregivers"

Financially, Vitamin D supplements cost pennies a day, Dawson-Hughes said, whereas the American Academy of Orthopaedic Surgeons estimated the cost of treating a hip fracture was $26,912 in 2007.

Dawson-Hughes adds that older adults, unless they are exposed to bright, year-round sunlight, require supplementation to meet their vitamin D needs. Typically, adults consume 150 IUs per day from food sources such as tuna or salmon or fortified milk. On average, multivitamins contain 400 IUs of vitamin D and there are individual vitamin D supplements with 400, 800 or 1,000 IUs. While vitamin D toxicity is rare, the IOM suggests capping intake at 4,000 IUs per day.

Dawson-Hughes said the results of the current study would be strengthened by large interventional trials investigating the impact of vitamin D supplementation on fracture risk. She and the authors also call for further investigation of the impact of combining calcium supplementation with high doses of vitamin D, as their data was inconclusive.

This study was supported by a Swiss National Foundations Professorship Grant and grants from the European Commission Framework 7 Program and DSM Nutritional Products.