Chapter 6 114 to magnesium citrate. Finally, we addressed the effects of a relatively high dose of various magnesium supplements on blood pressure, plasma magnesium and 24-urinary magnesium excretion as secondary outcomes. Methods Study population We recruited overweight and slightly obese participants via posters in the hospital and advertisements in local newspapers. Furthermore, we approached volunteers who participated in an earlier study in the University Medical Center Groningen (UMCG). Details of the in- and exclusion criteria have been described previously 15. In brief, subjects were 45-75 year-old non-smokers, with a stable body weight (weight gain or loss ≤ 3 kg in the past three months) and a body mass index (BMI) between 2535 kg/m2. We included overweight and slightly obese subjects, because they were expected to have increased arterial stiffness and blood pressure at baseline, allowing for improvement by the intervention 10,19. Furthermore, we excluded pre-menopausal women to reduce possible variations in the study outcomes due to hormonal effects (<2 years after last menstruation). Individuals with a high dietary magnesium intake (urinary magnesium excretion ≥7.0 mmol/24 h for men and ≥5.9 mmol/24 h for women), or high fasting levels of plasma glucose (≥7.0 mmol/L), total cholesterol (≥8.0 mmol/L) and triglycerides (≥2.2 mmol/L) were also not eligible for the study. Participants were instructed to continue any pre-existing medication without alterations throughout the study. All subjects provided written informed consent before the screening visit. The study was conducted according to the Declaration of Helsinki and ethics committee approval was obtained from the UMCG, The Netherlands (METc2017/220). The study was registered at clinicaltrials.gov as NCT03632590. The procedures followed were in accordance with the UMCG guidelines. The data that support the findings of this study are available from the corresponding author upon reasonable request. Study design In this randomized, double-blind, placebo-controlled, parallel-group trial, 164 study participants were randomly assigned to either receive a magnesium citrate supplement, a magnesium oxide supplement, a magnesium sulfate supplement or placebo, all in capsules with identical appearance, smell and taste. The capsules were provided by Laboratorium Medisan (Heerenveen, The Netherlands), which also conducted the
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