Can iron improve BMD and reduce LBW births?

Dietary iron may be almost as important as calcium in preserving bone mineral density (BMD), and it may help reduce the risk of low birthweight (LBW) deliveries. At least that's the suggestion gleaned from two recent studies.

Researchers used dual energy x-ray absorptiometry (DEXA) to assess BMD at five sites (lumbar spine, trochanter, femur neck, Ward's triangle, and total body) in 242 healthy nonsmoking postmenopausal women participating in the Bone, Estrogen, and Strength Training (BEST) Study.

They found that increases in dietary iron intake were significantly associated with increases in BMD at every site (P< 0.01), even after adjusting for protein and/or calcium. BMD among women with the highest iron intake was as much as 14% higher than was observed among those with the lowest intake. The investigators also found a synergistic effect at several bone sites between iron (>20 mg) and calcium (800­1,200 mg/d), although no such association was evident in women taking more or less calcium.

In a separate investigation, researchers randomized 275 low-income pregnant women in Cleveland with a hemoglobin concentration > 110 g/L and a ferritin concentration > 20 µg/L (i.e., iron-replete and not anemic) to take either 30 mg of iron as ferrous sulfate or placebo daily until 28 weeks' gestation. At 28 and 38 weeks' gestation, women with a ferritin concentration of 12 to <20 µg/L or <12 µg/L received 30 and 60 mg Fe/d, respectively.

While the iron capsules didn't significantly affect the overall prevalence of maternal anemia in the third trimester or the incidence of preterm births, infants born to woman taking iron were on average 206 g heavier at birth (206 ± 565 g; P=0.01). Similarly the incidence of LBW at term was 4%, compared with 17% in the placebo group (P=0.003), and there was a significantly lower incidence of preterm LBW (3% vs. 10%; P=0.017).

Harris MM, Houtkooper LB, Stanford VA, et al. Dietary iron is associated with bone mineral density in healthy postmenopausal women. J Nutr. 2003;133:3598-3602.

Cogswell ME, Parvanta I, Ickes L, et al. Iron supplementation during pregnancy, anemia, and birth weight: a randomized controlled trial. Am J Clin Nutr. 2003;78:773-781.