BOSTON, MASSACHUSETTS. Hip fractures caused by osteoporosis are a serious problem especially among postmenopausal women. Conventional wisdom has it that a high daily intake of milk and/or calcium from food and supplements will go a long way towards avoiding such fractures. Several trials of calcium supplementation have indeed shown that a high calcium intake increases bone density, but longer term studies have not found that this translates into a reduced risk of hip fractures. It is also clear that any possible benefits of calcium supplementation are reversed fairly quickly if supplementation is discontinued.
Researchers at the Harvard Medical School have just completed a study to determine the relative benefits of milk consumption and calcium and vitamin D supplementation. Their study involved 72,337 postmenopausal nurses who were enrolled in 1980 and followed for 18 years. During this time 603 (0.8%) of the nurses experienced a hip fracture. The study participants had completed food frequency questionnaires and supplied data regarding their supplement intake every two years since enrollment. After correcting for other variables affecting hip fracture risk, the researchers found no statistically significant protective effect of a high daily intake of milk or of a high intake of calcium from food or supplements. They did, however, observe that women who consumed more than 500 IU (12.5 mcg) per day of vitamin D from food or supplements had a 37% lower risk of hip fracture than did women whose daily vitamin D intake was less than 140 IU (3.5 mcg). The researchers point out that about 60% of the women in the survey had vitamin D intakes below those recommended by the Food and Nutrition Board (400 IU for women between the ages of 51 and 70 years and 600 IU for women older than 70 years). They also point out that the amount of vitamin D produced by exposure to sunlight decreases significantly with age (due to thinning of the skin) and the use of sunscreens. They further suggest that the reason why milk showed no significant protective effect may be due to its content of vitamin A which recently has come under scrutiny in regard to its possible role as a negative factor in bone health.
The researchers conclude that women should ensure an adequate daily intake of vitamin D either through
the use of supplements or through increased consumption of dark fish such as swordfish, salmon, bluefish,
mackerel or sardines.