Biology of Humans 6th Edition by Judith Goodenough,Betty McGuire

Exercise 1

Women, especially postmenopausal women, are often encouraged to take daily calcium supplements to keep their bones dense. However, as we will see in Chapter 6, calcium is also important in muscle contraction, including that of heart muscle. For this reason, Mark Bolland and his colleagues investigated the effect of calcium supplements on cardiovascular disease. In this study1, the participants were randomly assigned to a placebo group or to a group that took calcium and vitamin D supplements. The authors conclude, "Calcium supplements (without coadministered vitamin D) are associated with an increased risk of myocardial infarction [heart attack]. As calcium supplements are widely used these modest increases in risk of cardiovascular disease might translate into a large burden of disease in the population. A reassessment of the role of calcium supplements in the management of osteoporosis is warranted."
In the study discussed above, the participants self-reported any cardiovascular events. However, in a second study2, which was conducted by the same author team, researchers verified cardiovascular events from hospital discharges. In this study, there was only a modest increase in cardiovascular events. Why might this change in procedure have influenced the results