Critical thinking about three meta-analyses: can vitamin D alone or with calcium prevent fractures?

Critical thinking is crucially important in both research and practice. This article demonstrates that a lack of critical thinking in two meta-analyses resulted in a conclusion that contradicts another meta-analysis and popular opinions. Kahwati et al. and Zhao et al. drew a conclusion that "Vitamin D supplementation alone or with calcium was not associated with reduced fracture incidence among community-dwelling adults without known vitamin D deficiency, osteoporosis, or prior fracture", which apparently contradicted that of Tang et al. Kahwati et al. and Zhao et al. meta-analyzed vitamin D and/or calcium supplementation, which can decrease fracture risk factors, in a population with no known disorders of bone metabolism or vitamin D deficiency. They concluded that supplementation did not reduce fracture incidence. It is important to note that osteoporosis, which supplementation can prevent, and fractures are two distinct concepts. Zhao et al. presented their conclusion without including the conditions under which their conclusion was true. Subsequently, their conclusion was misleadingly interpreted by the public media as "Vitamin D and Calcium Don't Prevent Bone Fractures" and "Vitamin D Does Not Prevent Falls, Calcium Does Not Prevent Fractures-A $2 Billion Waste of Money". If study conclusions do not specify the applicable conditions, guidelines on medications, including supplements, are clinically unacceptable. Researchers must critically think about every step of their studies, including the way their conclusions are presented.