From The October 1999 Issue of Nutrition Science News
Customers who think of strengthening bones probably think of calcium, not fruit, vegetables and whole grains. But one theory explaining osteoporosisthe disease process that reduces bone masssuggests that the body buffers acid created during food metabolism by removing calcium from bone, which ultimately depletes the skeleton. Potassium and magnesium, both found in fruits and vegetables, help buffer acid and therefore may protect bone.
This theory led Katherine Tucker, Ph.D., of the U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, to study bone density as it relates to potassium and magnesium, and fruit and vegetable intake in people older than 70. Tucker used data from the ongoing Framingham Heart Study, a longitudinal study of people in Framingham, Mass., in which participants have been examined every two years since 1948.
For the 1988 examination, 345 men and 562 women with an average age of 75 filled out a food-frequency questionnaire and had their bone density measured in four sites: three hip areas and the arm. Tucker and colleagues looked for a correlation between the participants' food intake and their bone density. Four years later, bone density measurements were repeated on 229 men and 399 women. Their 1988 diet was correlated with the change in bone density that had occurred during the subsequent four years.
Men and women whose diets contained more potassium, magnesium, fruits and vegetables had higher bone mineral density. Bone mineral density increased between 2 and 5 percent with each 1,000 mg/day increase in potassium or 100 mg/day increase in magnesium. Men with higher initial intakes of potassium, magnesium, a combination of the minerals, or fruits and vegetables also had a smaller decline in bone mineral density during the four-year study. Researchers were puzzled, though, because food intake did not predict women's rate of bone loss.
Tucker also found that the average intake of calcium, magnesium and vitamin D among participants was considerably lower than government recommendations of 800 mg, 280-350 mg and 200 IU, respectively. There is no RDA for potassium. The most significant source of potassium in the study was potatoes. Whole wheat bread provided the most magnesium. Orange juice, skim milk and bananas were important sources of both minerals.
Potassium, Magnesium, and Fruit and Vegetable Intakes are Associated with Greater Bone Mineral Density in Elderly Men and Women
American Journal of Clinical Nutrition 1999 (Apr); 69 (4): 727-736