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New research clarifies roles of calcium, vitamin D, and protein in bone health, fracture risk

June 06, 2006

New research shows calcium in food might do more to protect bones than supplemental calcium in pill form, according to results presented at the IOF World Congress on Osteoporosis in Toronto, Canada. Bones lose calcium as they age, making them vulnerable to osteoporosis and fractures.

"We found that people who take just dietary calcium, or a combination of dietary calcium with supplements, have better bone density than those who take supplements alone," explained Dr. Reina Armamento-Villareal of the Washington University School of Medicine, St. Louis, MO (conference abstract P696). "So we think dietary sources are better than supplemental sources by themselves."

In separate presentations, researchers from the Netherlands report that vitamin D supplements reduce fracture risk only in the presence of additional calcium; a new study finds vitamin D deficiency is widespread among European women; and researchers from California add to a growing consensus that high protein foods also promote bone health.

IOF's Bone Appetit campaign, a global initiative focused on the role of nutrition and food in bone health, to be launched on World Osteoporosis Day 2006, 20 October, make these findings especially timely.

Dietary calcium more beneficial than calcium supplements

Clues to Armamento-Villareal's discovery were identified in women split into three groups: one that got calcium from supplements only; another that got it from food only; and a third that got calcium from both supplements and food. Dietary sources were associated with high levels of active estrogen metabolites in urine, which is important because estrogen builds bone mass during youth and prevents bone loss during aging. "And we believe that if urinary levels of estrogen metabolites are high then estrogen levels in the body are also high," Armamento-Villareal said.

According to Armamento-Villareal, dietary calcium appears to be optimally absorbed by the body. But Armamento-Villareal cautioned the study didn't reflect calcium intake patterns over a lifetime, so some uncertainties about the long-term differences between dietary and supplemental calcium remain.

"Our future plan is to conduct a two to three year study comparing their effects during growing years to determine if one source of calcium is better than the other in building bones," she said.

Bone fracture, vitamin D, and calcium

Calcium's bone strengthening benefits don't accrue in isolation—vitamin D also promotes healthy bone mass by enhancing calcium absorption. Now, researchers from Belgium and the Netherlands report that high dose vitamin D supplements taken for osteoporosis prevention and treatment need sufficient calcium to be effective (conference abstract OC21).

The discovery builds on findings by Heike Bischoff-Ferrari from the Geneva University Hospital in Switzerland, who showed previously that supplemental vitamin D at doses of 800 international units or more protects against bone fractures. The Bischoff-Ferrari, et al. study was unable to assess the role of calcium in that protection, however.

Dr. Steven Boonen of the Leuven University Center for Metabolic Bone Diseases, in Belgium, and colleagues from Brussels University and Amsterdam University in the Netherlands, followed up with a broad literature search addressing the role of both calcium and vitamin D protection against hip fracture risk. The investigation showed that even at 800 international units per day, vitamin D could not protect against hip fracture in the absence of additional calcium. "Our meta-analysis shows there are two requirements for vitamin D to be effective," Boonen said. "First, you need the appropriate dose of vitamin D, as indicated by Ferrari, et al., and second you have to combine that dose with calcium."

Not Enough Vitamin D

In a different study, Dr. Olivier Bruyere of the University of Liege, Belgium, and his colleagues showed that most post-menopausal women living in Europe may be deficient in vitamin D, putting them at elevated risk of bone loss and fractures (conference abstract P142SA). Experts suggest the body needs at least 50 to 80 nanamoles per liter of vitamin D in blood serum for optimal bone health.

Bruyere and his colleagues analyzed vitamin D levels in 8,532 European postmenopausal women. Among the women, nearly 80% had circulating vitamin D levels below the high end of the acceptable range. Roughly one third of the women had levels lower than 50 nanamoles per liter, suggesting they have a serious risk of osteoporotic fractures.

Bruyere said the findings were consistent regardless of whether the women lived in sun-drenched countries or not. This is remarkable because vitamin D is produced in the skin by a reaction that requires sunlight. "That's one of the interesting outcomes of our study,"

Bruyere says. "We tested women from France, Belgium, Denmark, Italy, Holland, Hungary, Spain, the UK, and Germany but the findings were independent of latitude. So, based on that, we could hypothesize that vitamin D levels might be low all over the world."

The researchers observed identical levels of vitamin D deficiency in women aged lower than 70. Bruyere suggests these complimentary findings indicate that age has little bearing on the degree of deficiency. "Even young post-menopausal women should take some form of vitamin D supplementation," he said. "Supplements should not be restricted just to the elderly."

Is Protein Good for your Bones?

While the protective effects of calcium and vitamin D have been repeatedly demonstrated, the role of dietary protein is less clear. Some studies suggest too much protein heightens fracture risk, in part by causing calcium to leach from the bones. But insufficient protein might also increase fracture risk by reducing bone mass.

In new research, Donna Thorpe and colleagues from Loma Linda University, California report that protein protects against wrist fracture in post-menopausal women (conference abstract P111). The study compared dietary preferences disclosed by 1,865 women during the mid-1970s, with their incidence of wrist fracture over the next 25 years. In what Thorpe describes as the study's strongest finding, high-protein vegetable sources—including nuts, beans, soy, and commercial vegetarian dishes—protected vegetarian women from wrist fracture. Therefore, Thorpe said, as long as vegetarian women get enough dietary protein, they won't increase their risk of osteoporosis, as some have suggested. Cheese and meat consumed three times a week or more were also found to be protective." As women age, they tend to eat less protein, so this study tells me we that we have to get sufficient dietary protein to those who are at high risk for fracture," Thorpe said.

International Osteoporosis Foundation