Extra Calcium Does Not Prevent Weight Gain Among Overweight/Obese Patients

Abstract & Commentary

By David Kiefer, MD. Dr. Kiefer is Clinical Instructor, Family Medicine, University of Washington, Seattle; Clinical Assistant Professor of Medicine, University of Arizona, Tucson; and Adjunct Faculty, Bastyr University, Seattle; he reports no financial relationship to this field of study.

Synopsis: This randomized, double-blind, placebo-controlled trial measured the effect of 1,500 mg of calcium carbonate daily on total body weight and body fat mass in 340 overweight and obese individuals. After two years, both the placebo group and the calcium group showed equal gains in total body weight and body fat mass, leading the researchers to conclude that supplemental calcium is not effective in preventing weight gain in this population.

Source: Yanovski JA, et al. Effects of calcium supplementation on body weight and adiposity in overweight and obese adults: A randomized trial. Ann Intern Med 2009;150:821-829.

The search continues for dietary changes or supplements that can help spur improvements in the obesity epidemic.1 This research trial was an attempt to extrapolate from previous research connecting calcium and weight loss, and determine whether calcium supplementation would prevent weight gain in already obese or overweight adults. Previous research had shown that in some cases people on lower-calcium diets may gain more weight than people consuming higher amounts of calcium, and that calcium may help both dieters and non-dieters to lose weight, all of which could be accounted for by calcium's ability to decrease fatty acid absorption while increasing adipocyte triglyceride deposition.2

The authors of this clinical trial recruited volunteers aged 18-80 from the Washington D.C. area who had a body mass index (BMI) of at least 25 kg/m2. Potential participants were excluded from the study for any of a variety of medical conditions, if they used daily supplemental calcium or vitamin D in excess of 300 mg or 400 IU, respectively, or if they were women and had been told by their health care provider to take calcium supplementation for any reason. At the end of the screening process, a total of 340 individuals (72% women) were randomized to either calcium carbonate (1,500 mg of elemental calcium) or placebo, taken in divided doses twice daily with meals, and followed for two years. Study parameters followed included body weight, fat mass, blood pressure, food diaries, and levels of serum 25-hydroxyvitamin D and serum parathyroid hormone.

At baseline, 39% of the participants were overweight (BMI = 25-29.9 kg/m2), 61% were obese (BMI ≥ 30 kg/m2), and 75% had dietary calcium intake less than the recommended 1,200 mg daily. Seventy-five percent finished the two-year trial (equal numbers in the treatment and placebo groups), and the results were analyzed using intention-to-treat statistical analyses.

Over two years, participants gained an average of 1.31 kg total body weight (0.82 kg in body fat mass), showing no difference between the calcium group and the placebo group. There was also no difference in BMI, abdominal circumference, hip circumference, triceps skinfold thickness, dietary or supplemental calcium intake, mood, or energy level. Subgroup analyses by race and gender also found no differences. Of note, serum parathyroid concentration decreased in the calcium group compared to the placebo group (P < 0.001), which the researchers interpreted as further corroborating the compliance that was noted during pill counts. The authors concluded that 1,500 mg daily of elemental calcium failed to alter weight or fat gain over two years in overweight or obese individuals.

Concerns about this trial were mentioned by the authors. Past trials showing small decreases in weight gain paired supplemental vitamin D with calcium, though this trial noted similar serum 25-hydroxyvitamin D levels in each group, possibly debunking the role that vitamin D played in these results. As with many dietary recall questionnaires, small relevant changes in substances or foods ingested may have been missed; in particular, baseline dairy calcium intakes may have confounded the effects of supplementation. In addition, the researchers pointed out that because the vast majority of study participants were women, the broad applicability of these results is lessened.

Commentary

Industrialized countries are facing an epidemic of obesity and obesity-related health problems, and the race is on to find any and all possible "cures." The medical literature is rife with the weight-loss effects of low-carbohydrate diets or low-fat diets (and all combinations thereof), diets that emphasize low glycemic index foods, several pharmaceuticals, and a variety of dietary supplements purported to block dietary fat absorption, increase metabolism, or change fat mass to lean muscle mass. Some researchers are examining subsets of patients who are insulin-resistant, realizing that weight-loss recommendations for them may be different than for individuals who are insulin-sensitive. There are also some people, more so in the lay press than scientific community, calling into question the premise that weight and weight loss are merely an "energy in, energy out" phenomenon. (Do we merely have to tell our patients to exercise more?) This complexity and the evolving science make it easy to understand why a simple supplemental nutrient, such as calcium, would be an attractive magic bullet to put an end to, in the case of this trial, undesired weight gain.

The "negative" results of this double-blind, placebo-controlled trial are on one level no surprise; the failure to show benefits of calcium supplementation on future weight gain in an "at-risk" population (overweight and obese individuals tend to gain more weight over time than people at normal BMI) could probably have been predicted. For example, neither continued weight gain with low-calcium diets (as demonstrated in some past studies), nor augmented weight loss during calcium-supplemented dieting, are even in the same ball park as the hypothesis proposed by these researchers. It is possible that entirely different mechanisms are at work in low-calcium vs. high-calcium states, and weight loss vs. prevention of weight gain scenarios in dieting or non-dieting people.

The myriad exclusions in the recruitment of people for randomization in this trial is also a major problem. To exclude any women who received recommendations for calcium supplementation from their health care providers surely leaves an interesting subset, especially given how common knowledge is regarding the importance of calcium supplementation. There potentially is some lifestyle, dietary, or behavioral correlate not measured by these researchers that could have affected how such a non-calcium-using group responded or didn't respond to this intervention. Not to mention the lack of applicability given that most of our female patients presumably are taking calcium (hopefully on our professional recommendations).

Another issue is that dovetailing these results with prior research proves difficult. Past trials have followed either dairy calcium levels or calcium supplementation or both, and tried to correlate this with body composition changes, or changes in weight, in a variety of different populations. It is possible that calcium from dairy behaves differently physiologically from calcium supplements, or that certain demographics (as briefly discussed above) respond differently to certain inter-ventions. In addition, there is the issue of calcium form (carbonate, citrate, gluconate, etc.) and absorption, and which one(s) may best achieve desired clinical outcomes.

Finally, it seems the authors had low expectations for already overweight and obese individuals, merely hoping to curtail their weight gain, rather than fostering weight loss. Of course, the latter is the therapeutic goal in improving risk for the many weight-related comorbidities already identified.

References

1. Kiefer D. Supplements commonly used for weight loss: What's the skinny? Altern Med Alert 2006;9:90-94.

2. Trowman R, et al. A systematic review of the effect of calcium supplementation on body weight. Br J Nutr 2006;95:1033-1038.