Calcium supplementation for people with overweight or obesity.

BACKGROUND: Obesity is a major health problem worldwide as it can lead to high blood pressure, heart disease, stroke, diabetes, and insulin resistance. The prevalence of overweight and obesity is increasing worldwide across different age groups. There is evidence of an inverse relationship between calcium intake and body weight. The clinical relevance of a small reduction in body weight has been questioned. However, at a population level, a small effect could mitigate the observed global trends. OBJECTIVES: To assess the effects of calcium supplementation on weight loss in individuals living with overweight or obesity. SEARCH METHODS: We searched CENTRAL, MEDLINE, Embase, LILACS (Latin American and Caribbean Health Science Information database), and two clinical trials registries. The date of the last search of all databases (except Embase) was 10 May 2023. No language restrictions were applied. SELECTION CRITERIA: We included randomised controlled trials evaluating the effect of calcium in participants with overweight or obesity of any age or gender. We excluded studies in participants with absorption problems. We included studies of any dose with a minimum duration of two months. We included the following comparisons: calcium supplementation versus placebo, calcium-fortified food or beverage versus placebo, or calcium-fortified food or beverage versus non-calcium-fortified food or beverage. We excluded studies that evaluated the effect of calcium and vitamin D or mixed minerals compared to placebo. DATA COLLECTION AND ANALYSIS: We used standard methodological procedures expected by Cochrane. Our primary outcomes were body weight, health-related quality of life, and adverse events. Our secondary outcomes were anthropometric measures other than body weight, all-cause mortality, and morbidity. MAIN RESULTS: We found 18 studies that evaluated the effect of calcium compared to placebo or control, with a total of 1873 randomised participants (950 participants in the calcium supplementation groups and 923 in the control groups). All included studies gave oral calcium supplementation as the intervention. We did not find any studies evaluating calcium-fortified foods. We excluded 38 studies, identified four ongoing studies, and listed one study as 'awaiting classification'. Sixteen studies compared calcium supplementation to placebo; two studies compared different doses of calcium supplementation. Doses ranged from very low (0.162 g of calcium/day) to high (1.5 g of calcium/day). Most studies were performed in the USA and Iran, lasted less than six months, and included only women. Low-certainty evidence suggests that calcium supplementation compared to placebo or control may result in little to no difference in body weight (mean difference (MD) -0.15 kg, 95% confidence interval (CI) -0.55 to 0.24; P = 0.45, I2 = 46%; 17 studies, 1317 participants; low-certainty evidence). We downgraded the certainty of the evidence by two levels for risk of bias and heterogeneity. None of the included studies reported health-related quality of life, all-cause mortality, or morbidity/complications as outcomes. Only five studies assessed or reported adverse events. Low-certainty evidence suggests a low frequency of adverse events, with no clear difference between intervention and control groups. Moderate-certainty evidence shows that calcium supplementation compared to placebo or control probably results in a small reduction in body mass index (BMI) (MD -0.18 kg/m2,95% CI -0.22 to -0.13; P < 0.001, I2 = 0%; 9 studies, 731 participants) and waist circumference (MD -0.51 cm, 95% CI -0.72 to -0.29; P < 0.001, I2 = 0%; 6 studies, 273 participants). Low-certainty evidence suggests that calcium supplementation compared to placebo or control may result in a small reduction in body fat mass (MD -0.34 kg, 95% CI -0.73 to 0.05; P < 0.001, I2 = 97%; 12 studies, 812 participants). AUTHORS' CONCLUSIONS: Calcium supplementation for eight weeks to 24 months may result in little to no difference in body weight in people with overweight or obesity. The current evidence is of low certainty, due to concerns regarding risk of bias and statistical heterogeneity. We found that the degree of heterogeneity might be partly explained by calcium dosage, the presence or absence of a co-intervention, and whether an intention-to-treat analysis was pursued. While our analyses suggest that calcium supplementation may result in a small reduction in BMI, waist circumference, and fat mass, this evidence is of low to moderate certainty. Future studies could investigate the effect of calcium supplementation on lean body mass to explore if there is a change in body composition.

Integrated health system intervention aimed at reducing type 2 diabetes risk in women after gestational diabetes in South Africa (IINDIAGO): a randomised controlled trial protocol.

INTRODUCTION: South Africa has a high prevalence of gestational diabetes mellitus (GDM; 15%) and many of these women (48%) progress to type 2 diabetes mellitus (T2DM) within 5 years post partum. A significant proportion (47%) of the women are not aware of their diabetes status after the index pregnancy, which may be in part to low postnatal diabetes screening rates. Therefore, we aim to evaluate a intervention that reduces the subsequent risk of developing T2DM among women with recent GDM. Our objectives are fourfold: (1) compare the completion of the nationally recommended 6-week postpartum oral glucose tolerance test (OGTT) between intervention and control groups; (2) compare the diabetes risk reduction between control and intervention groups at 12 months' post partum; (3) assess the process of implementation; and (4) assess the cost-effectiveness of the proposed intervention package. METHODS AND ANALYSES: Convergent parallel mixed-methods study with the main component being a pragmatic, 2-arm individually randomised controlled trial, which will be carried out at five major referral centres and up to 26 well-baby clinics in the Western Cape and Gauteng provinces of South Africa. Participants (n=370) with GDM (with no prior history of either type 1 or type 2 diabetes) will be recruited into the study at 24-36 weeks' gestational age, at which stage first data collection will take place. Subsequent data collection will take place at 6-8 weeks after delivery and again at 12 months. The primary outcome for the trial is twofold: first, the completion of the recommended 2-hour OGTT at the well-baby clinics 6-8 weeks post partum, and second, a composite diabetes risk reduction indicator at 12 months. Process evaluation will assess fidelity, acceptability, and dose of the intervention. ETHICS AND DISSEMINATION: Ethics approval has been granted from University of Cape Town (829/2016), University of the Witwatersrand, Johannesburg (M170228), University of Stellenbosch (N17/04/032) and the University of Montreal (2019-794). The results of the trial will be disseminated through publication in peer-reviewed journals and presentations to key South African Government stakeholders and health service providers. PROTOCOL VERSION: 1 December 2022 (version #2). Any protocol amendments will be communicated to investigators, Human Ethics Research Committees, trial participants, and trial registries. TRIAL REGISTRATION NUMBER: PAN African Clinical Trials Registry (https://pactr.samrc.ac.za) on 11 June 2018 (identifier PACTR201805003336174).