Nov. 29, 1999 (Atlanta) -- For pregnant women receiving low amounts of calcium in their diet, taking calcium supplements averaging 1,300 mg a day during the second and third trimesters of pregnancy can increase the bone mineral content of their fetus by about 15%. However, according to a study in the October issue of the journal Obstetrics & Gynecology, for women who receive adequate calcium in their diets, calcium supplements are unlikely to result in much improvement in fetal bone mineralization. Babies born with better mineralization have stronger bones and a boost to their development.
This new study, done at the University of Tennessee in Memphis, involved 256 women in their fourth month of pregnancy. Half the women were given up to two grams of supplemental calcium carbonate per day while the others were given a placebo. The women were checked for the effects of the supplementation up until they gave birth. One week after birth, the infants underwent x-ray studies of their whole bodies to check for bone mineral content.
The results found that for mothers with the lowest rate of calcium intake (less than 600 mg per day), the total skeletal bone mineral content was significantly higher in infants of calcium-supplemented mothers compared to the calcium-deficient placebo group. The babies from mothers with adequate calcium in their diet, who were given supplements, had about the same mineral content as the mothers in their corresponding placebo group.
According to the lead author, Winston W. K. Koo, MD, now at Wayne State University/Hutzel Hospital in Michigan, supplementation's minimal effect on fetal bone mineralization in women with adequate dietary calcium intake may be due to a "maternal homeostatic response." In other words, the mother's body may protect the fetus by decreasing the absorption and retention of calcium at very high rates.
The results of the study do not mean women shouldn't take the supplements. Pregnant women do have additional calcium needs and the supplements provide for those needs. Rather, this new research shows that if the mother's diet provides adequate amounts of calcium and she also takes supplements, there is little or no effect on the fetus.
Koo notes that low maternal calcium intake appears to critically affect fetal bone mineralization, and warns that calcium-poor diets can occur even in societies where food is plentiful. Other research shows that calcium deficiencies can also lead to preeclampsia, a condition during pregnancy characterized by high blood pressure, swelling, and weight gain greater than one pound per day. Studies show the risk of preeclampsia is between 45% and 74% lower for women who received calcium supplementation.
Koo says the best way to assure normal fetal bone mineralization is for the mother to eat sufficient amounts of calcium-rich foods. "Calcium-rich foods are also rich in other nutrients critical to bone health [such as vitamin D]," says Koo.
Calcium is found primarily in milk and milk products, although broccoli and canned fish are also good sources. For women who are lactose intolerant, green leafy vegetables, tofu, canned salmon and sardines (with bones) are good sources of calcium.
A number of studies show that between 30% and 50% of women fail to consume enough calcium to meet the new RDA of 1,200 mg each day. "We often find that women calcium-deficient in their diets can't tolerate or simply don't like calcium-rich foods, especially dairy products," Ray L. Howell, MD, at East Atlanta Obstetrics and Gynecology Associates in Conyers, Ga., tells WebMD. "Even if everything else they eat is fine, their calcium levels are below where they should be."
- In pregnant women who do not consume enough calcium in their diet, taking supplements can increase the bone mineral content of their children, but for those who do get enough calcium, additional supplements do not have this effect.
- Pregnant women should continue taking supplements as they have additional calcium needs that provide maternal and fetal benefits.
- Low intake of calcium during pregnancy is associated with poor fetal bone mineralization and increased risk of preeclampsia.