Women who have habitually low levels of calcium in their diet undergo significant changes in bone calcium turnover during pregnancy and lactation, according to the results of a new study.

Dr. Janet C. King, of Children’s Hospital Oakland Research Institute, California, and colleagues examined calcium levels during pregnancy and early lactation in 10 Brazilian women. The average level of dietary calcium was 463 milligrams per day, the researchers report in the American Journal of Clinical Nutrition.

The women were given a form of calcium that could be easily detected as it moved through the body, so bone calcium turnover could be monitored in different compartments. Evaluations were performed during early pregnancy (10 to 12 weeks), late pregnancy (34 to 36 weeks), and early lactation (7 to 8 weeks after birth).

A significant increase in the rate of bone calcium deposition was observed from early to late pregnancy, the researchers found. Compared with early pregnancy, the rates of bone calcium resorption were higher during late pregnancy and early lactation.

They also observed a positive relationship between bone calcium turnover and dietary calcium from early pregnancy to early lactation. Dietary levels of calcium and levels of insulin-like growth factor 1 explained 68 to 94 percent of the variability in bone calcium balance.

Summing up their findings, King and colleagues say that a positive bone calcium balance occurred only during late pregnancy, whereas calcium losses of about 90 milligrams per day was seen during early pregnancy and early lactation.

The researchers believe that further studies should address the effects of higher levels of calcium in the diet or calcium supplements on maternal and fetal bone mass, long-term changes in bone mass and calcium levels during pregnancy, lactation and after lactation in other groups of women who have low dietary calcium levels.

SOURCE: American Journal Clinical Nutrition, February 2006.