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Calcium: the “Weighty” Mineral
October 5, 2009
An evaluation of the link between higher calcium intake and lower body weight and/or less weight gain over time…
Affecting various body systems and aiding in a multitude of body functions, calcium is an essential macromineral and, not surprisingly, the most plentiful mineral in the body. While much is known about the role of calcium in body functions, there remains substantial speculation as to its possible role in both the promotion of health and the prevention and treatment of disease. One such speculation examines the promising link between higher calcium intake and lower body weight and/or less weight gain over time. With rates of obesity steadily rising and the prospect of a predominantly overweight nation looming, heightened efforts are being taken in order to counter the weight gain or to improve weight loss capabilities. Thus the proposed link between higher calcium intake and lower body weight and/or less weight gain over time has attracted, and will continue to attract, the interest of many. Several studies have been undertaken in order to evaluate the link and while results have been mixed, they are not insignificant.
What is Calcium?
Calcium is a naturally occurring mineral found in both the human body and foods. It may also be found in dietary supplements, most often in the forms of citrate or carbonate, as an additive in some foods, or even in some medications. Although calcium is primarily stored within bones and teeth, it may also exist within muscles, intercellular fluids, and blood. Affecting body systems such the circulatory, endocrine, nervous, and skeletal systems, calcium aids in a multitude of body functions. These functions include the support of bone and teeth structure, the transmission of impulses, the secretion of enzymes and hormones, the expansion and contraction of blood vessels, and the contraction of muscles (http://ods.od.nih.gov/factsheets/calcium.asp).
Calcium and a Healthy Diet
For adults and children age four and older, the daily value of calcium is set at 1,000 mg by the U.S. Food and Drug Administration. There are three main sources— food, dietary supplements, and medicine— of calcium and adults and children may satisfy their daily value from any combination of these sources (http://ods.od.nih.gov/factsheets/calcium.asp).
Common food sources of calcium include dairy and nondairy products. Low fat yogurts, cheeses, milks, and cottage cheese are all common diary product sources of calcium whereas sardines, calcium-fortified orange juice, kale, and calcium-fortified cereal are all common nondairy product sources of calcium (http://ods.od.nih.gov/factsheets/calcium.asp).
Dietary supplements contain elemental calcium, most often in the forms of carbonate or citrate. Both forms are well absorbed but absorption is dependent on total amount of elemental calcium consumed at one time. As the amount contained in supplements varies it is important to note the calcium by weight. In addition, supplements may induce adverse side affects such as constipation or bloating (http://ods.od.nih.gov/factsheets/calcium.asp).
Image from: http://www.tums.com/abouttums.aspx
Many antacid products contain calcium carbonate as it serves to neutralize stomach acid. Products such as Rolaids and Tums may contain as little as 200 mg or as much as 400 mg of elemental calcium and thus medicines are a viable source of calcium for some individuals (http://dietary-supplements.info.nih.gov/factsheets/calcium.asp).
The Link Between Higher Calcium Intake and Lower Body Weight and/or Less Weight Gain Over Time
There are several explanations that have arisen as to the mechanism by which this link operates. According to an article by Shrager (2005), there are two main hypothesized explanations that are serving as the driving force behind the attempts to confirm the link. The first of these explanations is that dietary calcium has an intracellular effect on the levels of calcium contained within adipocytes. The higher intake of calcium ceases the production of two hormones that are responsible for the stimulation of lipogenesis (formation and storage of fat) and the inhibition of lipolysis (breakdown of fat). The diminishing of these hormones has a reversal effect on lipogenesis and lipolysis and thus the adipocytes may break down the fat instead of forming and storing it. The second explanation relies on the inhibitory effect of calcium on fatty acid absorption in the gastrointestinal tract. Calcium intake is correlated with the binding of fatty acids and higher intakes may result in more binding. When fatty acids are bound, they are excreted, as opposed to absorbed, and therefore increased calcium intake would result in more excretion and less absorption of fatty acids (Shrager, 2005). A multitude of studies have been undertaken in order to evaluate the supposed link and results have been mixed. Capitalizing on the results from studies supporting the link are several companies, primarily based in diary production, that have begun marketing their products under slogans or campaigns that highlight the supposed link. Caution should be taken when analyzing any of the studies and/or products as bias and sales profits are often underlying such statements. Furthermore, as recognized in a review by Heaney et al. (2000), weight loss is a “highly multifactorial variable” and thus it is hard to link one factor, such as higher calcium intake, to something that is so susceptible to confounding variables (Heaney et al., 2000).
What Claims are Being Made?
The predominance of claims being made can be traced to companies based in dairy production such as Yoplait and the support of the “got milk?” campaign. Featured in Yoplait’s “Spotlight on Health” is the consumption of Yoplait Light yogurt as part of the “Boost Your Weight Loss Plan”. The early studies of Dr. Michael Zemel, in which he found support for the link between higher calcium intake and lower body weight, are cited and although his study was based upon general dairy intake, Yoplait Light yogurt has been superimposed on the dairy aspect of the study. In doing so Yoplait not only suggests a positive correlation between higher calcium (dairy) intake and weight loss, but also suggests that Yoplait products are responsible for the weight loss (http://www.yoplaitusa.com/health_archive_boost.aspx).
The “got milk?” campaign mirrors that of the Yoplait. Using the images of well-known models, athletes, musicians, and actors to appeal to the public consumer, the “got milk?” campaign seeks to promote milk drinking and, consequently, profits for the industry. Considering that an entire link of the www.whymilk.com website is devoted to studies, it is not surprising that a multitude of studies supporting the link between higher calcium intake and weight loss and/or less weight gain over time are noted. Coupled with the milk mustache images of the above-mentioned, well-known individuals, the public is left with the impression that milk is directly, and positively, associated with thinness, health, and all other qualities that the “got milk?” representatives embody (http://www.whymilk.com/healthy_weight.php). But do the relevant clinical trials support these claims?
Do Relevant Clinical Trials Support These Claims?
Much of the initial examination of the link was supported by studies employing animal subject models. In a study by Bursey et al. (1989), the weight of both lean and fatty Zucker rats was lowered by a high-calcium diet and a more recent study by Zemel et al. (2000) produced comparable results (Bursey et al., 1989). In the study by Zemel et al. (2000), energy-restricted aP2-transgenic augoti mice served as models and were separated into high and low calcium diet treatments. From this trial, four main conclusions were drawn regarding the link and hypotheses were formed concerning the mechanisms by which it functions. The first conclusion was that “a basal low calcium diet caused an increase in body weight, fat pad mass and basal andipocyte [Ca2+]”. The second was that “high-calcium diets caused a reduction in body weight, fat-pad mass, and basal adipocyte [Ca2+]”. The third was that “high-calcium diets suppressed lipogenesis and stimulated lipolysis” and the fourth was that “high calcium diets promoted thermogenesis” (Zemel et al., 2000). It was also observed that, although administered in like fashions, the effect of dairy calcium was of a far greater quantity. Thus from this study it can be concluded that “high-calcium diets suppressed adipocyte [Ca2+], stimulated lipolysis, inhibited lipogenesis, and caused an increased white adipose tissue UCP2 expression and a corresponding increase in core temperature. Consequently, dietary calcium facilitates reduction of fat tissue mass and body weight in kilocalorie restriction by modulating energy metabolism, which serves to reduce energy storage and increase thermogenesis” (Zemel et al., 2000).
Following the success of the above studies, the findings were then applied to human subjects. In a second study by Zemel et al. (2004), the link between higher calcium intake and lower body weight was examined. 41 obese (initial BMI’s between 30.0 to 39.9 kg/m2), adults, ranging in age from 18 to 60, were enrolled and subjected to two weeks of baseline data collection. Following the physiological and dietary data collection in which an estimate of caloric needs was established, 32 men and women continued to the 24-week portion of the randomized, placebo-controlled trial. Included on the criteria of their initial BMI’s, low-calcium diets (500-600 mg/d), less than 3 kg weight change over the preceding 3 months, and lack of change in exercise intensity or treatment over the preceding 3 months, the participants were then randomly assigned to one of three treatment groups. Treatment 1 (low-calcium) consisted of 10 participants who received zero to one serving of dairy products each day and 400-500 mg of calcium each day in addition to a daily placebo supplement. Treatment 2 (high-calcium) consisted of 11 participants whose treatment was identical to that of treatment 1, except with the placebo replaced by an additional 800 mg of calcium for a total of 1200-1300 mg of calcium each day. Treatment 3 (high-dairy) consisted of 11 participants who received three servings of dairy products each day for a total of 1200-1300 mg of calcium each day. The diets of all treatment groups provided for a 500 kcal/d deficit and were monitored via review of daily diet diaries and pill counts and physical activity and tobacco use were kept at the same levels of that during the two weeks of baseline data collection. All participants experienced weight and fat loss due to the 500 kcal/d deficit but the losses “were markedly increased on the high-dairy diet, with intermediate, but still significant, effects on the high-calcium diet” (Zemel et al., 2004). Treatment 1 lost 6.4 ± 2.5 % of their body weight, treatment 2 lost 8.6 ± 1.1%, and treatment 3 lost 10.9 ± 1.6 % of their body weight and fat loss mirrored this trend in each treatment group. As the two treatment groups receiving higher intakes of calcium lost more body weight, this study supports the link between higher calcium intake and lower body secondary to caloric restriction. In addition, it begins to examine the difference between dietary and supplemental sources of calcium, lending evidence that dietary sources may have a greater effect than supplemental sources (Zemel et al., 2004).
The second speculated link, that between higher calcium intake and less weight gain over time, was examined in a study by Yanovski et al. (2009). 340 overweight (BMI’s between 25 and 30 kg/m2) adults were determined eligible according to the criteria of an age between 18 and 80, a BMI greater than 25 kg/m2 and freedom from significant medical diseases. After initial assessment in which weight, height, abdominal and hip circumference, tricep skinfold thickness, blood pressure, total body fat mass, intact parathyroid hormone contractions, serum 25-hydroxy-vitamin D, baseline dietary calcium intake, and energy intake were evaluated, the participants were randomly assigned to one of two treatment groups for a two-year period of study. Treatment 1 received 1500 mg of elemental calcium, in the form of calcium carbonate, and treatment 2 received placebo. Both treatments were administered as capsules to be taken twice daily with meals. Every 3 months the participants completed questionnaires regarding medication adherence, assessment of general health, and self-reports of physical activity, hunger, stress, and mood. Every 6 months unused study medications were exchanged for new supplies, which also assessed adherence, and at the conclusion of the study, a survey regarding treatment assignment was administered. Body weight and body fat mass were measured at the end of each year as were fasting anthropometric measurements, body composition (by DEXA), blood pressure, and a questionnaire regarding dietary and supplemental calcium intake was administered. 75% of participants completed the two-year period of study and among all participants (from both treatment groups) there was +1.31±6.5kg change in body weight and +0.82±4.3kg change in fat mass. The between-group differences were +0.02kg for change in body weight and +0.39kg for fat mass and were rendered not statistically or clinically significant with or without adjustment analysis for age, race and sex. In addition, any changes in abdominal and hip circumference, tricep skinfold thickness, and other body compositions were also not statistically or clinically significant. Thus it was concluded “dietary supplementation with 1500 mg/d of elemental calcium for 2 years had no statistically or clinically significant effects on weight in overweight and obese adults. Calcium supplementation is unlikely to have clinically significant efficacy as a weight gain preventive measure in such patients” (Yanovski et al., 2009). Limitations that should be taken into consideration for this study include the majority of female participants (245 of the 340), and the portion of funding provided by the Office of Dietary Supplements, which may have biased results. In addition, the study did not include subjects randomized to a high dairy calcium diet and according to the Zemel et al. (2004) study, dietary sources may have a greater effect than supplemental sources (Yanovski et al., 2009).
A study of similar design examined the effects of higher calcium intake on weight gain over time in pubertal girls. In a study by Lappe et al. (2004), 59 girls participated in a two-year pilot study in which they were assigned to either the treatment or control group. The treatment group of 27 girls, 9 years of age, was instructed to follow a diet that supplied at least 1500 mg of calcium per day while the control group of 32 girls, 9 years of age, was instructed to follow their usual diet. The usual diet had been assessed during screening and thus the girls participating in the study have usual diets consisting of less than 1100 mg of calcium per day. 3-day food diaries were completed once every 3 months and assessed quarterly as was height, weight, BMI, lean and fat mass, and pubertal status. Following the completion of the 2-year study, mean calcium intake was reported as 731±105 mg/day for the control group and 1,366±193 mg/day for the treatment group. Despite the treatment group consuming almost double the amount of calcium as the control group, weight and lean and fat mass did not significantly differ. For the treatment group there was a 34% increase in weight, a 31% increase in lean mass, and a 38% increase in fat mass. For control group mean increases were: weight 33%, lean mass 31%, and fat mass 33%. Based on these results it was determined that a high-calcium diet does not significantly impact weight gain over time (Lappe et al., 2004).
A number of reviews have also been published which seek to reevaluate the results of several studies in order to form a well-researched conclusion regarding the link between higher calcium intake and lower body weight and/or less weight gain over time. A review by Heaney et al. (2000), reevaluated five clinical studies (4 observational and 1 double-blind, placebo-controlled, randomized) that encompassed 780 women of varying age groups. Negative associations of the relationship between body weight and calcium intake were recognized and an estimation of 1000 mg calcium intake difference was mapped to an 8 kg difference in mean body weight. However it was estimated that calcium intake explains only ~3% of the variance in body weight. Thus it was concluded that “body weight is a highly multifactorial variable, and it is unlikely that a very large fraction of its variability could be attributed to any single factor. Also the imprecision of the methods for estimating calcium and protein intakes renders estimates of the independent variable inherently uncertain” (Heaney et al., 2000).
A follow up, extended review by Heaney et al. (2002) examined six observational studies and three controlled trials and concluded that there is a “consistent effect of higher calcium intakes, expressed as lower body fat and/or body weight, and reduced weight gain at midlife” (Heaney et al., 2002). The results of the studies were normalized to produce the following statistic correlation. According to Heaney et al. (2002), “with each 300 mg increment in regular calcium intake there is an association with ~1 kg less body fat in children and 2.5–3.0 kg lower body weight in adults”, implying support for the link (Heaney et al., 2002).
A meta-analysis performed by Shapses et al. (2004) combined data from three clinical trials. All trials were 25 weeks, randomized, placebo-controlled, and double-blind. In the trials, 100 premenopausal and postmenopausal women received either the treatment of 1000 mg per day calcium supplementation or the control placebo. Body weight and fat mass were assessed as the dependent variable and the means for the combined data were as follows. For the women receiving treatment, body weight change was -6.2±0.7 and fat mass was -4.5±0.6. For the women receiving placebo, body weight change was -7.0±0.7 kg and fat mass was -5.5±0.6 kg. The differences were not deemed significant and thus this meta-analysis does not lend support for the speculated link. However, the study did note that “over a longer period of time and with a larger number of subjects, a reliable effect might be observed” (Shapses et al., 2004).
One of the most inclusive reviews, by Lanou and Barnard (2008), examined 49 clinical trials and based upon classification of the trials by energy restriction and dairy or calcium treatment, concluded that 41 of the trials had no effect. Furthermore, of the 8 showing effect, two demonstrated weight gain, one showed a lower rate of gain, and ﬁve showed weight loss. Based upon these mixed results, it was concluded that “the majority of the current evidence from clinical trials does not support the hypothesis that calcium or dairy consumption aids in weight or fat loss” (Lanou and Barnard, 2008). The review does offer a possible explanation as to the inconsistency of the results. It recognizes the “associations between higher consumption of dairy products and dietary or lifestyle habits, such as exercise, increased ﬁber or fruit and vegetable intake, decreased soda intake, etc., that aid in achieving and maintaining lower weights and body fat levels” (Lanou and Barnard, 2008). More simply, there are confounding variables that may be influenced by calcium intake and therefore the variables, not calcium intake, may truly be associated with weight loss.
Conclusion: Does Higher Calcium Intake Lower Body Weight and/or Less Weight Gain Over Time?
Calcium clearly plays an important role in many body functions. As for its role in weight loss and/or less weight gain over time, the function becomes a bit unclear. While some studies support the link, others refute it. This is not surprising considering weight loss is influenced by hundreds of variables that can change from person to person. Thus until more consistency is found between studies and a direct relationship is defined, higher calcium intake should not be employed as a primary weight loss mechanism. Perhaps it may be most beneficial as a supplemental, secondary mechanism but even so considerations should be taken.
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