Printer Friendly

No bones about it: calcium is confusing.

For decades, women have heard: "Make sure to get enough calcium; maybe even take a daily calcium supplement!" Calcium is key to building and maintaining strong bones and, for women, there is particular focus on preventing osteoporosis and broken bones (especially broken hips), making us a key audience for companies selling calcium supplements. The real story on calcium is not so simple, however, and scientists are still trying to sort out the good and bad of both dietary calcium and calcium supplementation.

Severe calcium deficiencies are often caused by diseases like parathyroid problems, and have negative health effects like muscle and heart issues. (1) Inadequate calcium intake causes deficiencies that, while less severe, can lead to bone problems when the body takes the calcium it needs from the skeleton. (This is why women often hear they should get enough calcium to help prevent osteoporosis.)

We also know about some of the negative effects caused by high calcium levels. For example, high intake of calcium supplements may increase the risk of kidney stones. (2) The Women's Health Initiative (WHI) and Nurses' Health Study both found associations between taking calcium supplements and kidney stones, although the risk seems to be higher from calcium supplements than calcium from food.'

While we often hear about calcium's importance for strong bones, researchers are also exploring whether the mineral might help decrease cancer risks. Some studies suggest that higher calcium intake may reduce the risk of colorectal cancer, although the National Cancer Institute (NCI) says these results "have not always been consistent," and thus does not recommend increasing calcium to help prevent this cancer. (3) It is unclear if higher calcium intake could help reduce the risk of breast or ovarian cancers. Study results vary; moreover, some studies explore dietary rather than supplemental calcium, while others find different results in pre-menopausal and post-menopausal women, making it hard to generalize about calcium's potential benefits.

Another question is whether calcium supplementation during pregnancy can reduce the risk of gestational hypertension and/or preclampsia. Here again, the scientific evidence is limited and conflicting. Some authors have suggested that calcium supplementation might be useful in reducing these risks, but others have failed to find a benefit. A systematic review of this topic conduced by the Federal Agency for Healthcare Research and Quality (AHRQ) (4) noted that a Cochrane review (5) found calcium supplementation lowered the risk for preeclampsia during pregnancy by half But, this effect did not appear in the other studies reviewed, including the larger, randomized controlled trials. The authors conclude that "the effects of calcium supplementation on preeclampsia are unclear," and "there is no clear answer to whether calcium supplementation is effective for preventing high blood pressure (with or without proteinuria) in pregnancy" (1)

Based on its own review, the Food and Drug Administration (FDA) said it was "highly unlikely that consuming calcium supplements during pregnancy would reduce the risk of pregnancy-induced hypertension or preeclampsia." (6) Other authors conclude, "because all pregnant women require at least 1 g[ram] of calcium per day, calcium supplementation is important for all women with low dietary calcium irrespective of its effects on HDP [hypertensive disorders of pregnancy], pre-eclampsia and preterm birth." (7)

Most recently, controversy about calcium has centered around heart disease. This area is confusing to begin with because calcium is a component of the plaque that builds up in our arteries, and coronary calcium scans look at this calcium as an indicator of heart disease. (8) Women who are familiar with coronary calcium scans may assume that extra calcium from supplements is worse for the heart--but the topic is more complex than that.

Although it's been proposed that calcium might help reduce hypertension, heart disease, and stroke, some researchers have found either no or negative effects. (1) In 2010, a meta-analysis using WHI data reported that taking calcium supplements was associated with about a 30% increase in the incidence of heart attacks, which attracted a lot of attention. (9) The authors explained that none of the included trials were intended to look primarily at cardiovascular outcomes, however, and there was no finding of increased stroke or death among participants who took calcium supplements. Others criticized the meta-analysis for not addressing the common combination of calcium and vitamin D in supplements, which may have affected the results because vitamin D affects how much calcium can be absorbed. (1)

One of the meta-analysis' authors later reanalyzed the data to try to account for participants' personal calcium and vitamin D supplementation and assess whether they affected the meta-analysis results. The re-analysis concluded that "calcium supplements with or without vitamin D modestly increase the risk of cardiovascular events," especially heart attack. The authors called for "a reassessment of the role of calcium supplements in osteoporosis management" due to this increased risk. (10) The Federal Office of Dietary Supplements, however, examined the topic in general and the re-analysis specifically and (while noting the need for further investigation), stated: "overall, the totality of evidence to date does not support a link between calcium and cardiovascular disease risk." (1)

Confused? It would be hard not to be! Right now, just about every resource states that more research is needed, and hopefully new studies will clarify the situation.

We are usually advised to get our nutrients primarily from foods rather than from supplements, so we may find that getting more calcium from food has fewer risks than taking supplements. While many women get less calcium than is recommended, and supplements may be needed sometimes, there is a lot of uncertainty about how calcium supplements affects women's cancer and heart disease risks. (1) Until we know more, you may want to talk to your health care provider about what nutrients you might lack, and the best way to add them into your diet.

References are available online or from editor@nwhn.org

Rachel R. Walden, MLIS is a medical librarian and blogger for Women's Health News and Our Bodies Our Blog.
COPYRIGHT 2011 National Women's Health Network
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2011 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Walden, Rachel
Publication:Women's Health Activist
Date:Nov 1, 2011
Words:993
Previous Article:Unplanned and unwanted pregnancies account for up to half of all U.S. pregnancies.
Next Article:Why is science under fire?
Topics:

Terms of use | Privacy policy | Copyright © 2018 Farlex, Inc. | Feedback | For webmasters