The effect of lactation on peak adult shaft and ultra-distal forearm bone mass in women.

The effect of long-term vs short-term lactation (three to four children with an average of 10.7 mo vs 2.8 mo duration for each child) on maternal forearm bone-mass sites that are either primarily trabecular or cortical in composition was determined. The habitual calcium intake of each subject exceeded 90% of her recommended dietary allowance (RDA) for nonpregnant, pregnant, and lactating states. Trabecular and cortical bone mass were estimated using single-photon densitometry at ultra-distal and midshift sites on the radius, respectively. Bone mass at both sites was lower in the long-term than in the short-term lactation group and, at the ultra-distal site (trabecular bone), the effect was statistically significant (p less than 0.05). These data indicate that even when women consume the RDA for calcium, long-term lactation can deplete ultra-distal bone mass in the forearm.