ZURICH, Switzerland, and DENVER, Colorado—As little as 400 IU/day of extra vitamin D can reduce fracture risk by up to 20%, but vitamin D insufficiency is increasing in the US population and is particularly severe in African Americans and Mexican Americans, according to 2 studies reported in the March 23 issue of Archives of Internal Medicine.^1,2  Other researchers earlier linked low vitamin D levels to chronic pain problems.³

The two new studies show that:

• vitamin D supplements of at least 400 IU/day reduce non-vertebral fractures by 20%
• vitamin D supplements of at least 400 IU/day reduce hip fractures by 18%
• vitamin D doses less than 400 IU/day do not reduce either fracture type
• additional calcium did provide further protection against fractures if vitamin D doses were >400 IU/day
• serum 25(OH)D levels in the US population have been dropping steadily since 1994
• 97% of non-Hispanic African Americans are now vitamin D-insufficient
• 90% of Mexican Americans are vitamin D-insufficient.

Heike Bischoff-Ferrari, DrPH, of the University of Zurich, University Hospital, Zurich, Switzerland and colleagues performed a meta-analysis on 12 previously published clinical trials of oral vitamin D supplements among adults age 65 or older. These double-blind randomized controlled trials involved 42,279 participants (average age 78) and looked at non-vertebral fractures, including 8 trials of 40,886 participants specifically studying hip fractures.

Vitamin D's dose-dependent effect

“Our study shows that the earlier uncertainty regarding the benefit of vitamin D on non-vertebral fracture prevention is explained by its dose-dependent benefit. Low dose vitamin D of 400 IU per day or less does not prevent fractures. However, a daily dose of at least 482 IU, ideally 800 IU per day, of vitamin D reduces non-vertebral fractures significantly by at least 20%,” Dr. Bischoff-Ferrari told MSKreport.com.

“Notably,” Dr. Bischoff-Ferrari added, “at the higher dose, this benefit is not restricted to frail older individuals, as suggested by earlier meta-analyses, but is also present in community-dwelling older individuals. Also, at the higher dose, the vitamin D benefit on fracture prevention appears to be the same with or without additional calcium supplementation and independent of age (65 to 74 or 85+ years). Finally, the benefit of vitamin D may be best if given as vitamin D3 (cholecalciferol) compared to vitamin D2 (ergocalciferol). In the subgroup of community-dwelling older individuals age 65-74, vitamin D3 at the higher dose reduced non-vertebral fractures by 33%,” Dr. Bischoff-Ferrari said.

Vitamin D levels still dropping in US

Average blood levels of vitamin D suggest that current recommendations for vitamin D supplementation may be far too low, conclude researchers led by Adit A. Ginde, MD, MPH, of the University of Colorado Denver School of Medicine, Aurora.

Using data from the Third National Health and Nutrition Examination Survey (NHANES III), Dr. Ginde compared serum samples collected in 1988-1994 to those collected during 2001-2004.

“We found that the mean serum 25(OH)D level in the US population dropped by 6 nanograms from the 1988-1994 to the 2001-2004 data collections. This drop was associated with an overall increase in vitamin D insufficiency to nearly 3 of every 4 adolescent and adult Americans,” Dr. Ginde reported.

Low vitamin D worsens chronic pain

This trend in vitamin D insufficiency has broad clinical implications in addition to the well-known association with osteoporotic fracture risk.

Mayo Clinic researchers led by Michael Turner, MD, reported last year that there is a correlation between inadequate vitamin D levels and the amount of opioid narcotic medication taken by patients who have chronic pain.3

Vitamin D: Translating research into practice

“The implications are: Vitamin D at a dose of more than 400 IU, best 800 IU, is an effective strategy to prevent non-vertebral fractures including those at the hip in individuals age 65 and older. Importantly, it is affordable to everyone and well-tolerated, thus a viable public health strategy,” Dr. Bischoff-Ferrari said.

Dr. Ginde's group concluded that current recommendations for dosage of vitamin D supplements are inadequate to address this growing epidemic of vitamin D insufficiency. They recommend 1,000 IU per day or more, particularly during the winter months and at higher latitudes, and “judicious sun exposure.”

“The primary risk factor of non-vertebral fractures and especially hip fractures at higher age is falling. Thus, effective prevention strategies should target both bone and muscle health. Vitamin D has been shown to reduce fractures both by its benefit on bone, but likely even more important, through its benefit on muscle and fall reduction. Several trials have shown fall reduction with vitamin D. The potential of vitamin D is that it covers a dual pathway (bone and muscle) so important for fracture prevention at higher age,” Dr. Bischoff-Ferrari said.

References

1. Bischoff-Ferrari HA, Willett WC, Wong JB, et al. Prevention of nonvertebral fratures with oral vitamin D and dose dependency. Arch Intern Med 2009;169:551-561.
2. Ginde AA, Liu MC, Camargo CA. Demographic differences and trends of vitamin D insufficiency iin the US population, 1988-2004. Arch Intern Med 2009;169:626-632.
3. Turner MD, Hooten WM, Schmidt JE, et al.  Prevalence and Clinical Correlates of Vitamin D Inadequacy among Patients with Chronic Pain. Pain Medicine 2008;9:979-984.