In preventing osteoporosis, an understanding of both the innate genetic and acquired environmental factors implicated in its pathogenesis is critically important. These two sets of factors interact with each other so closely that it is difficult to deal with each independently of the other. In our study, heritability for lumbar bone mineral density (BMD) between mother and daughter was estimated as 0.56 before menarche and 0.60 after menarche, suggesting that the genetic factors predominated over the environmental factors. At the same time, these values also suggest a not-so-small role for the environmental factors in determining lumbar BMD. Thus there is an important role suggested for medical intervention aimed at acquisition of BMD through management of lifestyle factors with familial phenotypic similarities in mind. It is suggested that the younger the candidate, the better the chance for intervention, and that consideration needs to be given to how best to intervene in the candidate before and after menarche or menopause during which estrogen secretion is seen to vary greatly.