The USDA’s Agricultural Research Service (ARS) has focused a good deal of effort on learning more about the role nutrition plays in boosting bone health. For instance, some ARS collaborative research found young girls who think they are lactose intolerant have curtailed their milk intake, resulting in decreased calcium intake and significantly decreased bone mineral density (BMD), compared to their peers who drank a steady amount of fortified milk. Further, actual tests showed some of the girls who thought they had intolerance did not, while other girls who had lactose intolerance didn’t realize it.
“We’re concerned that misperceptions about lactose intolerance can lead girls—in early adolescence—to cut back on milk,” said ARS physiologist Marta D. Van Loan, Ph.D., who authored research on the subject in 2007. “To do that during this phase of their critical bone-forming years could have lifetime consequences on the health of their bones.”
Van Loan and her team also looked at the effect of physical activity on bone strength and bone geometry in postmenopausal women, who are prone to osteoporosis due to decreased estrogen production following menopause. They found at least 30 minutes a day—or even four hours a week—of weight-bearing leisure-time activity such as walking, jogging or minor weightlifting helped maintain two important bone health parameters: cortical bone density (the thickness of bone’s hard outer layer) and functional geometry (such as the inner and outer diameter of the bone).
However, Van Loan and ARS have been less convinced on soy’s role in bone health, although research has stepped up since findings surfaced on the negative effects of traditional hormone replacement therapy. ARS and its collaborators have focused on soy isoflavones and protection against bone loss in postmenopausal women.
They published one trial in early 2010 in the American Journal of Clinical Nutrition (Jan;91(1):218-30) on two doses of soy isoflavone (80 mg/d and 120 mg/d) in postmenopausal women. The results from the trial, the longest of its kind, showed no significant positive effect on bone loss, compared to placebo. However, when factoring in lifestyle parameters, the 120 mg/d isoflavone dose appeared to modestly benefit bone loss prevention.
““The body’s response to isoflavones extracted from soy proteins may be different from its response to isoflavones in their natural matrix of soy protein or soy foods or in a soy-protein supplement,” Van Loan said. “It’s also possible that some soy-protein compound other than the extracted isoflavones was responsible for the bone-protecting effects seen in some studies. Or the doses of the isoflavones in our study may not have been high enough to produce a bone-sparing effect.”
Overall, ARS is investigating the calcium requirements of adults for adequate bone mass, relative to factors such as vitamin D intake and smoking. Former ARS biologist Curtiss Hunt has reported the recommended daily intake for calcium may be more than is necessary. His modeling of data collected from men and women at the Grand Forks USDA Human Nutrition Research Center, North Dakota,
suggested 741 mg/d is the average amount of dietary calcium needed to maintain a neutral calcium balance—when the amount of calcium consumed equals the amount of calcium lost through elimination. “The same model suggests that a calcium intake of 1,035 mg per day would cover the needs of 95 percent of the American adult population,” said LuAnn Johnson, statistician on the study. Ultimately, the subjects’ bodies were more efficient in keeping calcium when fed the lower amounts of calcium, whereas excess calcium was simply eliminated in those with higher calcium intake.
