In the present study, we observed that calcium+D supplementation for 12 weeks facilitated fat loss in very-low calcium consumers independent of energy restriction, which is concordant with other randomized controlled trials
[14, 16–20], suggesting a beneficial effect of calcium intake on weight management.
To our knowledge, ours is among the few relevant studies to evaluate the effect of combined calcium and vitamin D3 administration in very-low calcium consumers by setting initial calcium intake at <600 mg/day as one of the inclusion criteria. The mean initial calcium intake of subjects was estimated to be 409.7 mg/day, below the threshold previously suggested
 to predict promising outcomes of a weight-loss program. Previously published studies were carried out mostly in Western countries, where recruitment of participants with very-low calcium consumption was difficult because of the moderate level of calcium intake among the majority of Western populations: 856 mg/day for men and 670 mg/day for women in American adults; moreover, half of them use calcium supplements
. Whereas in the Chinese population, the average intake of calcium was around 390 mg/day, according to the Chinese National Nutrition and Health survey in 2002
. Therefore, this population provides a stable sample of very-low calcium consumers for investigating the potential anti-adiposity effect of calcium below the cut-off value of 600 mg/day. As expected, we observed significant augmentation of body fat loss and visceral fat loss in the calcium and vitamin D3 supplemented group after the intervention. In contrast, a 24-month trial
 found no significant difference in anthropometric variables between the calcium-supplemented group and placebo in subjects with initial calcium intake of 882 mg/d. Neither did Manios et al.
 or Wagner et al.
 observed any beneficial effect of calcium (with or without vitamin D) on weight management in subjects with over 650 mg/day of initial calcium intake, which constitutes one explanation for the inconsistency. The dosage used in calcium-supplemented programs was diverse. Zemel and his group
 detected a beneficial effect of calcium carbonate, an additional 800 mg/day, on weight reduction, which was increased by 26% compared with the control subjects. In Faghih’s study
, supplementation of 800 mg/day was also found to be effective in facilitating weight loss. Major et al.
 reported a significantly greater decrease in body weight and fat mass in the calcium+D group (5.8 vs. 1.4 kg and 4.7 vs. 1.2 kg, respectively), receiving 1200 mg calcium carbonate and 400 IU vitamin D daily. In the present study, however, the dose was administered as one tablet (600 mg calcium carbonate, 125 IU vitamin D) daily. We used a relatively lower dose because the initial calcium intake in the majority of Chinese is low. In most relevant studies carried out in Western populations the average calcium intake was around 600 to 800 mg/d (even higher in some studies), and the dose was about 1.5 times the initial calcium intake. And therefore, in the current study, the additional 600 mg/d was administered in subjects with initial calcium intake of around 400 mg/d. Besides, 125 IU of vitamin D3, which is linked with 600 mg of calcium in each tablet, was administered in the present study, since it is an over-the-counter supplement.
The current study recruited obese and overweight subjects with a lower body mass index (BMI) cutoff, which was believed to be required for Chinese population
[26, 27], who has a lower baseline BMI to begin with and the risk of cardiovascular diseases is doubled at BMI of 23.0 to 24.9, and tripled at BMI of 25.0 to 26.9
. In addition, we recruited subjects aged 18 to 25 years from colleges, because these students usually had similar dietary patterns and their compliance with dietary instructions was fairly good. This made it possible for us to evaluate the potential difference between an energy-restricted diet with calcium+D supplementation and energy restriction alone in a short period of 12 weeks. Actually, the compliance to the weight loss program was very good, since at the end of the study, subjects in both groups achieved 5~6% of body weight reduction, suggesting they were motivated by the intervention. In fact, reported energy intake was significantly lower in both groups at endpoint versus baseline. It is worth mentioning that the calcium+D group achieved 55.6% augmentation of fat mass loss compared with the control, despite the fact that there was no significant difference in body weight change between groups. That means the calcium+D group lost more adipose tissue during energy restriction.
The greater decrease in fat mass observed in the calcium+D group of the current study could result from several factors attributing to calcium metabolism. First, a calcium-rich diet is shown to increase fat oxidation
, promote fat cell apoptosis
, and reduce lipid absorption due to the formation of insoluble calcium-fatty acid soaps in the intestine, which are eventually excreted in the feces
. Second, high dietary calcium intake is associated with suppression of 1,25-dihydroxyvitamin D (1,25-(OH)2D) levels which in turn act to decrease calcium influx into the cell. These modifications consequently stimulate lipolysis and inhibit lipogenesis in the adipocyte
[10, 14]. Third, a calcium-specific appetite control, proposed by Tordoff, could have played a role in facilitating fat loss in a calcium-supplemented program
Moreover, the findings of the current study are concordant with the majority of previously published clinical trials showing no significant differences between treatment and control subjects in glucose and insulin profiles
 and in circulating lipids and lipoprotein concentrations
[32–34]. There is only one previous study
 reporting a significantly greater decreases in total:LDL, LDL:HDL (P<0.01 for both) and LDL cholesterol (P<0.05) after 15 weeks of intervention in the active group, receiving a supplementation of 1200 mg/day calcium and 400 IU vitamin D and a caloric deficit of 700 kcal/day, than in the placebo group, receiving 700 kcal/day of energy restriction alone. In addition, the present study showed no significant impact of additional elemental calcium+D on blood pressures. It seems that the antihypertensive effect of calcium may be more pronounced with dairy-derived calcium
[36, 37] than elemental calcium
[32, 34]. The former was examined in studies that carried out over short terms (5 weeks to 16 weeks), while the latter was used in moderate or long-term studies (6 months and 2 years). If that is the case, it is not surprising that we did not find any significant changes in blood pressure in such a short term. Besides, other minerals (potassium and magnesium) and bioactive peptides in dairy, which act as angiotensin converting enzyme inhibitors
, may also explain the antihypertensive effect in intervention trials. It will be interesting to conduct further research on the whey-derived bioactive peptides for blood pressure management.
The primary limitation of our study is that participants in the control group were not given a placebo due to budget constraints. However, in the present study the dietitians, supervising and giving dietary instructions to subjects, were not involved in any other procedures such as randomization allocation or evaluation of outcome measurements. Subjects in the present study made no communications with each other for their participation is confidential and individual. In addition, we avoided reporting any subjective measurements, such as hunger scores, as well, so as to minimize bias that could occur in an open-label trial. Not using dual energy X-ray absorptiometry (DEXA), the gold standard method for assessing body composition, constitutes another limitation. However, BIA is also a validated and reliable method to assess body composition
[13, 39]. Other limitations include the primarily female composition of the study sample, the relatively small dose of vitamin D3 used. From a statistical perspective, the beneficial effects of calcium+D supplementation on fat loss could be attribute to calcium as much as to vitamin D3. However, previously published literature tends to attribute a large contribution to calcium instead of vitamin D due to the controversial results and lack of evidence of the effect of vitamin D on adiposity
. Future research in this area should be oriented toward a better understanding of the dose–response effect of calcium supplementation (with or without vitamin D) on weight management by administering different dosages of this mineral.