# Evidence that calcium helps build strong bones

Physician scientists do experiments to answer questions like "Does calcium make the bones stronger?" There are several kinds of experiments that can be done. The best experiment is called a randomized double-blind clinical trial. A large number of people (in this case, children and teenagers) are divided into two groups. The larger the number, the more definite the results of the study. Each person is assigned to a group randomly, for example, by flipping a coin (actually, computers make a random number). All the kids in one group take a pill that has calcium in it; all the kids in the other group take a pill that looks exactly the same, but does not have calcium in it. This pill is called a placebo. Neither the kids nor the doctors doing the study know which person is taking the real pill and which one is taking the placebo. Only a statistician (somebody who does statistics, who does not ever see the kids and who keeps the information secret) knows which kids are taking the calcium. At the beginning of the study all the kids have a measurement of their bone strength called bone density. Then they take their pill during the study, which can last for several years. At the end of the study everyone has another measurement of the bone density. Finally, the statistician tells the doctors and the kids who was taking the real calcium and who was taking the placebo. They can tell if the average bone density was better in the group taking calcium than in the group taking placebo.

This graph shows the results of several such studies of calcium in young people. Each bar on the graph is a different study, and the height of the bar represents how much better the bone density was (% increase since beginning of study) in the calcium group than in the placebo group. You can see that all of the studies found that the bone density in the calcium group was better than the placebo group.

The best study (the first bar on the graph) was done by a doctor named Conrad Johnston, from Indiana. His team studied 140 kids aged 6 to 14. This study was really clever, because all of the kids were identical twins. One twin got the calcium pill and the other twin got the placebo. After three years the bone density was better in the twins taking the calcium. The reason this was such a good study is that the groups had exactly the same age, and almost exactly the same height and weight, because the kids were identical twins. Another indication that it was a good study is that the National Institutes of Health paid for the study, and not the company which makes the calcium pills.

These results are then published in medical journals so doctors can read all the details of the study. Of course, the best studies are published in the best journals. The summaries of the studies are now available to anyone on-line through the National Library of Medicine. Click on the link if you want to read the summary of Dr. Johnston's study. To read the entire study you would have to go to a medical library to find the journal.