Calcium and vitamin D are both necessary for strong bones, but does one have a greater impact on reducing the risk of osteoporosis and subsequent fractures than the other? Vitamin D received a boost from Harvard University researchers who found that D - but not calcium - was associated with lower hip fracture risk in a group of older women. The study was published in the American Journal of Clinical Nutrition.

Diet analysis

The participants were 72,337 healthy, postmenopausal women from the ongoing, prospective Nurses' Health Study (NHS), who had no history of osteoporosis or hip fracture. Every 2 years for 14 years, the volunteers provided information about their diet, health, and lifestyle, such as use of vitamin and mineral supplements, physical activity, smoking status, and hormone replacement therapy use. The women were followed for up to 18 years; the outcome of interest was fracture of the proximal femur following slight to moderate trauma.

D made a difference

The only nutrient that had a significant relationship with fracture risk was vitamin D. The highest vitamin D intake (>/= 12 µg/day from food and supplements) was associated with a 37% lower risk of hip fracture compared with the lowest vitamin D intake level, less than 3.50 µg/day (relative risk, or RR = 0.63; 95% CI: 0.42, 0.94; p for trend = 0.09).

Data analysis

These researchers conclude that vitamin D plays a more crucial role than calcium in preventing hip fractures, even though calcium is often promoted as the vital nutrient for strong bones and osteoporosis prevention. But that conclusion may be a bit premature, as numerous earlier studies have shown that adequate calcium intake can reduce bone loss and fracture risk. Most health professionals are in agreement that without an ample supply of vitamin D and sufficient calcium to replace obligatory losses, an increased rate of bone resorption can result in weak bones that are more susceptible to osteoporosis and fractures.

Advice to patients

While researchers will continue to study the effect of calcium and vitamin D on bone density, the message to patients is clear: both nutrients are needed for healthy bones. Many older adults do not get the recommended amounts of either nutrient, and these individuals might benefit from a daily supplement that includes both calcium and vitamin D.