To the Editor.
—We read with interest the article by Dr Sowers and colleagues1 on changes in bone mass of women who breast-feed their infants, in which they report that bone mass decreases at 6 months of lactation and is recovered at 1 year post partum. Although we consider their longitudinal study to be an important contribution, we would like to communicate two observations from our own experience.Changes in bone mass in women are influenced significantly by weight changes,2 weight being the main determinant of bone mass in women.3 Given the possibility of weight changes over a 1-year follow-up in longitudinal studies, as noted by other authors as well,4 changes in other body components should be considered when evaluating variations in bone mass.Bone mass varies seasonally and independently of weight. It decreases in winter and increases in summer.5 Therefore, 6-month variations should not
Rico H, Revilla M. Factors Affecting Bone Mass. JAMA. 1994;272(13):1003. doi:10.1001/jama.1994.03520130037022