The review may lead to a review of current recommendations, such as those of the American College of Obstetricians and Gynecologists from 2002, that stated: "Daily calcium supplementation has not been shown to prevent pre-eclampsia and, therefore, is not recommended."
However, data obtained since this statement in 2002 could lead to a revision of this stance.
Lead review author Dr. G. Justus Hofmeyr told NutraIngredients.com: "The findings of the review are that calcium supplementation reduces the risk of hypertension for pregnant women who have inadequate dietary calcium.
"Physicians are likely to recommend that women who are not able take adequate calcium in their diet, should take a calcium supplement."
The new review, published in the Cochrane Database of Systematic Reviews (2006, Issue 3), looks at 12 randomised controlled studies, one involving over 4,000 pregnant women in North America, and one conducted by the WHO involving over 8,000 women internationally.
The reviewers, led by Dr. Hofmeyr, head of the Department of Obstetrics and Gynaecology at East London Hospital Complex in South Africa, found that calcium supplementation was safe and a relatively inexpensive way to reduce blood pressure in women more likely to develop hypertension, as well as in women with low dietary calcium intake.
"Pregnant women from communities with low dietary calcium who received at least 1.5 grams of calcium by mouth [daily] during the second half of pregnancy had a lower risk of hypertension and pre-eclampsia, and of severe complications including death, than women who received placebo treatment," said Dr. Hofmeyr.
But when the reviewers considered women with better nutrition the benefits of increase calcium intake were slightly reduced.
"Women from communities with adequate dietary calcium had a small (10 percent) reduction in the risk of hypertension, but no significant reduction in the risk of preeclampsia or other adverse outcomes," said Hofmeyr.
Pre-eclampsia, affecting two to three per cent of all pregnancies, occurs when a mother's blood pressure rises to the hypertensive range, and excretion of protein in the urine becomes too high. It is estimated to be responsible for about 60000 deaths worldwide.
It is not known why some expectant mothers develop pre-eclampsia, and other attempts to use supplements, most notably the antioxidant vitamin C and E, have resulted in null results.
"Calcium supplementation may be of some benefit in reducing the morbidity associated with preeclampsia, and it does no harm," said independent pre-eclampsia expert, Dr. John Repke, chairman of obstetrics and gynecology at Penn State University College of Medicine.
"There is really almost nothing to lose from trying this approach, and based on this Cochrane Review, potentially something to be gained," added Repke, who was not involved with the review.
While the results of the review are highly promising, Dr. Hofmeyr told NutraIngredients that two questions remain unanswered at present:
"It remains to be answered whether lower doses of calcium supplementation than were used in the trials reviewed (1.5g or more daily), would be effective in reducing the risk of hypertension.
"It also remains to be answered whether assuring adequate calcium intake from before the pregnancy would be more beneficial than supplementation commenced once the woman is already pregnant."
It should also be stressed that expectant mothers, as well as all women of child-bearing age, should continue to eat folic acid-rich or fortified foods and/or take folic acid supplements to reduce the risk of neural tube defects.