A randomised, double-blind, placebo-controlled, parallel-arm study comparing the daily intake of 1500 mL - 1800 mL of magnesium bicarbonate supplemented spring water with non supplemented spring water (placebo) was undertaken in postmenopausal women, while on their usual diet, over an 84 day period. The study was conducted from 31 August 2005 to 3 November 2006 and approved by the St Vincent's Hospital Human Research Ethics Committee.
Ninety-one subjects attended the Clinical Trials Centre for screening for eligibility. All screened subjects provided written informed consent to participate in the study prior to commencement of screening procedures.
Only postmenopausal subjects aged 50 -70 years and with a body mass index (BMI) 20-35 kg/m 2were eligible. Subjects were excluded if physical and mental health status, including laboratory abnormalities, indicated serious or chronic illness (abnormal liver function tests (LFTs) or electrolytes, creatinine clearance < 60 mL/min, haemoglobin < 10 g/L), if they were intolerant to magnesium-containing products, taking certain medications (antacids other than proton pump inhibitors or H 2agonists, diuretics, calcium or magnesium supplements) or planned medication changes. Subjects using hormone replacement therapy (HRT) were to have been on a stable dose for at least one month prior to screening and continue this dose through the study. Subjects on special diets (including vegan, weight loss or high protein), those with a history of frequent use of magnesium based laxatives and substance abuse (including nicotine) were excluded.
Protocol - treatment
Of the 91 screened, 23 failed to satisfy the entry criteria and one was excluded due to poor venous access. The remaining 67 postmenopausal women were randomised in a 1:1 ratio to receive between 1500 mL and 1800 mL daily of magnesium bicarbonate supplemented spring water (650 mg/L bicarbonate, 120 mg/L magnesium, pH 8.3-8.5) (supplemented water group) or spring water without supplements (control water group) over three months (84 days). For those consuming the supplemented water, this volume resulted in a daily dose of 975 - 1170 mg bicarbonate and 180 - 216 mg of magnesium. There was no bicarbonate and negligible amounts of magnesium (< 5 mg/L) in the spring water given to the control group. Analysis of the spring water (control) was conducted by National Association of Testing Authorities (NATA) accredited (#1884) SONIC HEALTHCARE laboratory NSW and the constituents are listed in Additional file 1.
The water was supplied in 600 mL identical bottles so that subjects were blinded to the type of water they received. Subjects were at liberty to choose the time at which they consumed the water and were discouraged from drinking the study product with meals. The water could be chilled but not heated to be used in beverages such as tea or coffee, or for cooking. All study water consumed was recorded by subjects in the drink diary and bottle caps returned at each study visit to evaluate compliance, where 100% compliance was defined as daily consumption of between 1500 mL and 1800 mL of water. Subjects were requested to maintain consistency of nutritional habits and lifestyle behaviours throughout the study period.
Subjects were seen at Baseline and at Days 14, 42 and 84. Any changes in diet were noted. Blood and urine samples were collected at every visit to measure markers of bone turnover (PTH, 1,25-dihydroxyvitamin D and osteocalcin, urinary telopeptides, hydroxyproline) and pH. Serum fasting lipids (total cholesterol, HDL, LDL, triglycerides), serum biochemistry (albumin, alkaline phosphatase, alanine amino transferase [ALT], aspartate amino transferase [AST], bicarbonate, total bilirubin, chloride, calcium, creatine kinase, creatinine, fasting glucose, lactate dehydrogenase [LDH], magnesium, potassium, sodium, total protein, urea and uric acid) and haematology were measured at each visit. Urine was collected for 24 h for the measurement of calcium, phosphate, creatinine and free cortisol concentrations and excretion. Physical examinations were performed; including blood pressure (supine and standing); body weight recorded and adverse event reports were elicited at each visit.
All biochemical, haematology and urinalysis testing was performed by NATA accredited (#2115) Institute of Laboratory Medicine (SydPath) St Vincent's Hospital NSW.
The change from Baseline (Day 0) to each study visit at Days 14, 42 and 84 was compared between treatment groups for all biochemical, blood lipid, blood pressure, pH measures, haematological, urinalysis and bone turnover markers. Tables and figures present the mean and standard deviation (SD) for each parameter at baseline and at each visit. Continuous measures were compared across treatments using independent, two-sample, unpaired t-tests if the data were normally distributed, otherwise the Wilcoxon Rank Sum Test was used. Categorical measures were compared using Chi square or Fisher's Exact test. No adjustments were made for multiple testing as this was an exploratory study and it is acknowledged that there is an increased risk of making Type I errors given the number of tests performed.
Repeated measures analyses of variance were performed for all outcome variables, incorporating all visits from baseline to Day 14, Day 42 and Day 84 together with treatment group as factors in the analysis. If the p-value for the change in the variable was less than or equal to 0.10 then a generalised linear mixed model with a random intercept term (for subject) was fitted. The outcome in the model was the measure of interest at Days 0, 14, 42 and 84 and the model included the main effects of group and visit. The p-value from the test of the interaction between group and time was the result of interest and p < 0.05 was considered statistically significant.