Calcium may prevent polyps, but effect on cancer still not known, study finds

July 19, 2005

Although calcium supplements might prevent development of polyps that sometimes lead to colon cancer, there is not enough evidence that the mineral can prevent colorectal cancer itself, according to a new study.

The study, a review of two earlier well-designed randomized controlled trials, found a moderate protective effect on development of colorectal adenomatous polyps, the small, generally benign types that about 30 percent of middle-aged and older Americans have. But "this does not constitute sufficient evidence to recommend the general use of calcium supplements to prevent colorectal cancer," says an Israeli team of researchers headed by Michael Asher Weingarten of Rabin Medical Centre.

Polyps can lead to colorectal cancer if unchecked. Because it is difficult to conduct studies on the effect of preventive doses of calcium on colorectal cancer itself -- due to the relatively small number of cases and the length of time they could be watched -- the reviewers looked instead at prevention of polyps, which occur frequently in the population, as a potential predictor of later cancer.

Previous experiments in animals and surveys of people who had high calcium diets have indicated a possible protective effect. In looking at the two best studies done so far, Weingarten and colleagues found results that "suggest a clinically relevant protective effect of dietary calcium supplementation on the development of colorectal adenomatous polyps."

"Although it is likely to be safe, this ... would need to be more clearly demonstrated in further controlled studies before any attempt at widespread introduction into clinical practice," they say.

The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

Dr. Anca Zalmanovici, one of the review's authors, says "calcium supplementation is relatively cheap, likely to be safe, readily available and has other positive metabolic effects on conditions that occur with aging," such as osteoporosis, high blood pressure, kidney stones and weight gain.

If further studies confirm calcium as effective, the review says it could be given to people who had polyps before and who are thus are at higher risk of getting colorectal cancer.

The review cautions that higher doses of calcium taken over longer periods of time, while perhaps needed, also may not be well tolerated by some subjects. At the same time, it notes that no evidence exists that calcium supplements up to 2,000 mg a day would be detrimental to those taking such supplements. As a general rule, people need about 1,750 mg of calcium a day. Standard dosages for over-the-counter elemental calcium supplements range from 500 mg to 1,500 mg a day.

Doubts about the importance of dietary calcium have surfaced in a number of studies, according to the review, which points out that early findings of polyp- and cancer-inhibiting effects of calcium have not been confirmed by recent studies. The review also identified a major fecal occult blood-screening program that found no association between colon cancer and reported calcium intake.

The review focused on two double blind, placebo controlled trials involving 1,346 people, including participants with previous adenomas. A U.S.-based study involving six clinical centers used 1,200 mg of elemental calcium. A second study, conducted in nine European countries and Israel, used calcium supplements of 2,000 mg per day for three years.

Colon cancer is one of the leading cancers in men and women, and dietary factors - including calcium, fiber, sugar, fat, vegetables and meat -- have been considered involved in the increasing incidence of the disease in industrialized countries. The risk begins to increase after age 40 and rises sharply between 50 and 55 years old.

Calcium has been suggested as a protective agent against colorectal cancer because it is thought to inhibit processes considered critical to the growth of colon cancer cells. While calcium has been shown to have a protective effect in some animal and epidemiological studies, according to Dr. Weingarten, the evidence from other studies gave inconsistent results.

The review notes that a large randomized controlled trial by the Women's Health Initiative, which was begun in the early 1990s, will be deserving of attention when its findings are made known. The trial is expected to conclude in 2007. The trial is focused, in part, on the impact of calcium supplements on colorectal cancer and adenomas.
-end-
FOR MORE INFORMATION
Health Behavior News Service: 202-387-2829 or www.hbns.org.
Interviews: Contact Michael Asher Weingarten at 972-3-937-7340 or weingml@post.tau.ac.il
To receive a full copy of the review, contact Julia Lampam at 44-124-377-0668 or jlampam@wiley.co.uk

Weingarten MA, Zalmanovici A, Yaphe J. Dietary calcium supplementation for preventing colorectal cancer and adenomatous polyps. The Cochrane Database of Systematic Reviews 2005, Issue 3.

The Cochrane Collaboration is an international nonprofit, independent organization that produces and disseminates systematic reviews of health care interventions and promotes the search for evidence in the form of clinical trials and other studies of interventions. Visit http://www.cochrane.org for more information.

Center for Advancing Health

Related Cancer Articles from Brightsurf:

New blood cancer treatment works by selectively interfering with cancer cell signalling
University of Alberta scientists have identified the mechanism of action behind a new type of precision cancer drug for blood cancers that is set for human trials, according to research published in Nature Communications.

UCI researchers uncover cancer cell vulnerabilities; may lead to better cancer therapies
A new University of California, Irvine-led study reveals a protein responsible for genetic changes resulting in a variety of cancers, may also be the key to more effective, targeted cancer therapy.

Breast cancer treatment costs highest among young women with metastic cancer
In a fight for their lives, young women, age 18-44, spend double the amount of older women to survive metastatic breast cancer, according to a large statewide study by the University of North Carolina at Chapel Hill.

Cancer mortality continues steady decline, driven by progress against lung cancer
The cancer death rate declined by 29% from 1991 to 2017, including a 2.2% drop from 2016 to 2017, the largest single-year drop in cancer mortality ever reported.

Stress in cervical cancer patients associated with higher risk of cancer-specific mortality
Psychological stress was associated with a higher risk of cancer-specific mortality in women diagnosed with cervical cancer.

Cancer-sniffing dogs 97% accurate in identifying lung cancer, according to study in JAOA
The next step will be to further fractionate the samples based on chemical and physical properties, presenting them back to the dogs until the specific biomarkers for each cancer are identified.

Moffitt Cancer Center researchers identify one way T cell function may fail in cancer
Moffitt Cancer Center researchers have discovered a mechanism by which one type of immune cell, CD8+ T cells, can become dysfunctional, impeding its ability to seek and kill cancer cells.

More cancer survivors, fewer cancer specialists point to challenge in meeting care needs
An aging population, a growing number of cancer survivors, and a projected shortage of cancer care providers will result in a challenge in delivering the care for cancer survivors in the United States if systemic changes are not made.

New cancer vaccine platform a potential tool for efficacious targeted cancer therapy
Researchers at the University of Helsinki have discovered a solution in the form of a cancer vaccine platform for improving the efficacy of oncolytic viruses used in cancer treatment.

American Cancer Society outlines blueprint for cancer control in the 21st century
The American Cancer Society is outlining its vision for cancer control in the decades ahead in a series of articles that forms the basis of a national cancer control plan.

Read More: Cancer News and Cancer Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.