Individual components that define MetSyn include atherogenic dyslipidemia (alteration of blood lipid profile favouring atherosclerosis development and being characterized by high fasting blood triglycerides and low fasting blood HDL-cholesterol), elevated fasting blood glucose and (or) insulin resistance (more insulin is need to control/regulate blood glucose levels), elevated blood pressure, abdominal obesity and, most recently recognized, a pro-inflammatory and prothrombotic state [a state favouring inflammation and thrombus (blood clot) formation] (Zimmet et al 2005; Johnson et al 2006; Grundy et al 2006; Feldeisen et al 2007; Alberti et al 2009; Simmons et al 2010; Wree et al 2011).
The increasing number of individuals with MetSyn, in the past 10-15 years, has been associated with several different factors. Although the exact aetiology of the MetSyn still remains unclear, it is known to involve complex interactions between genetic, metabolic and environmental factors. Among environmental factors, diet and physical activity are of central importance in the prevention and treatment of this condition. Some minerals, like calcium, magnesium and potassium, generally deficient in MetSyn-inducing diets, due to a low ingestion of milk, dairy products, fruit, vegetables, whole grains, beans and nuts, like almonds and walnuts, have been proposed protective against the MetSyn (Feldeisen et al 2007).
Minerals and the Metabolic Syndrome. The high intake of sodium on one hand and the low intakes of potassium, calcium and magnesium on the other hand, produce and maintain elevated blood pressure in a big proportion of the population. Conversely, decreased intake of sodium alone, and increased intakes of potassium, calcium and magnesium, each alone, decrease elevated blood pressure. A combination of all these factors, that is, decrease of sodium, and increase of potassium, calcium and magnesium intakes, which are characteristic of the so-called Dietary Approaches to Stop Hypertension (DASH) diets, has an excellent blood pressure lowering effect (Van Leer et al 1995; Whelton et al 1997; Karppanen et al 2005; Geleijnse et al 2005; van Meijl et al 2008).
Research has indicated that low intake of magnesium, low blood magnesium concentrations and/or low intracellular magnesium levels may lead to and are associated with elevated blood pressure, MetSyn, insulin resistance, and/or type 2 diabetes mellitus (Song et al 2004; He et al 2006; Volpe et al 2008; Wells 2008). Experimental and clinical studies suggest that magnesium intake may decrease blood triglyceride and increase HDL-cholesterol levels (He et al 2006). Both individuals who did not have type 2 diabetes mellitus, but with insulin resistance and hypomagnesemia (low blood magnesium level), and individuals with type 2 diabetes mellitus, with hypomagnesemia, showed improved insulin sensitivity and, for type 2 diabetic individuals, improved metabolic control (lower fasting blood glucose and lower glycated haemoglobin levels), after oral magnesium supplementation (Song et al 2004; Volpe et al 2008; Wells 2008). A strong inverse relationship between magnesium levels in serum and the presence of MetSyn has been reported, in a population of overweight or obese individuals (mean age around 66 years), in which serum magnesium levels decreased as the number of components of MetSyn increased (Evangelopoulos et al 2008).
Epidemiological studies have suggested protective effects of dairy product consumption on MetSyn development. Additionally, it has been published that calcium supplements improve the serum lipoprotein profile, particularly by decreasing serum total and LDL-cholesterol concentrations (van Meijl et al 2008). In overweight or obese women (mean age 43 years), who were very low-calcium consumers, decreases in body weight, fat mass and spontaneous dietary lipid intake have been associated with calcium plus vitamin D supplementation, for 15 weeks (Major et al 2009). Based on the Korean National Health and Nutrition Examination Survey (2001 and 2005) calcium intake is inversely associated with the risk of having MetSyn in postmenopausal women (Cho et al 2009).
Drinking water and its mineral content. Several investigations evaluated the relationship between hardness of drinking water, or its content in magnesium and calcium, and the risk for cardiovascular disease or stroke. Results support the hypothesis that a low intake of magnesium in drinking water may increase the risk of dying from, and possibly developing, cardiovascular disease or stroke (Monarca et al 2006; Rylander 2008). An additional parameter to take into account is the acidity of the water (there is considerable evidence that acid-base conditions in the body influence the mineral homeostasis and it is known that acid load influences the reabsorption of calcium and magnesium in renal tubuli). It has been suggested that the health effects related to drinking water found in some studies may have been caused by an increased urinary excretion of minerals induced by acid conditions in the body and that drinking water should contain sufficient amounts of hydrogen carbonate to prevent this effect (Rylander et al 2006; Rylander 2008).
Natural mineral waters represent a substantial alkaline load and may influence mineral homeostasis in our body (Rylander 2008). Several papers in the literature point to calcium- and (or) magnesium-rich natural mineral waters as good sources of these ions (in which they are highly bioavailable), contributing to achieve their daily recommended intakes (Bohmer et al 2000; Sabatier et al 2002; Bacciottini et al 2004; Kiss et al 2004; Heaney 2006; Karagülle et al 2006).
It is interesting to mention that, besides the influence on MetSyn components (see below), the mineral content of natural waters may have other preventive/beneficial effects. It has been reported that in a Hungarian city the occurrence of preeclampsia varied pari passu with the magnesium content of the drinking water in different parts of the city (Melles et al 1992). In a different study, the consumption of 1L/day of a high calcium natural mineral water (supplement of 596 mg of calcium), for 6 months, reduced serum parathyroid hormone and indices of bone turnover in postmenopausal women with a low calcium intake (Meunier et al 2005).
Natural mineral waters and the Metabolic Syndrome components. Within the scope of beneficial effects in cardiovascular disease and MetSyn prevention, there are several publications showing that the ingestion of mineral waters with sodium bicarbonate is beneficial in lowering cardiovascular risk factors, including blood pressure (Luft et al 1990; Schorr et al 1996; Capurso et al 1999; Rylander et al 2004; Schoppen et al 2004; Almeida et al 2010a,b; Pérez-Granados et al 2010).
The consumption of 3L/day of a NaHCO3-containing mineral water, for 7 days, decreased systolic blood pressure, in mildly hypertensive men (Luft et al 1990) and the consumption of 1.5L/day of a sodium bicarbonate-rich mineral water, for 4 weeks, decreased mean arterial blood pressure, in elderly normotensive subjects (aged 60-72 years) (Schorr et al 1996). The daily ingestion of 0.5 mL of a portuguese natural mineral water rich in bicarbonate and sodium, Água das Pedras® (and with a higher content in magnesium, calcium and potassium than tap water from Porto city area, where the study took place), for 7 weeks, had no effect on blood pressure, in normotensive adults (aged 24-53 years) (Santos et al 2010). Also, administration of this natural mineral-rich water in an animal model of MetSyn did not increase blood pressure and improved some metabolic parameters (like plasma insulin and triglycerides levels) (Almeida 2010a,b).
Ingestion of a natural mineral water rich in calcium, bicarbonate and magnesium, as well as in sulphate, reduced blood pressure (systolic and diastolic) after 2 weeks (this reduction was kept until the 4 weeks of treatment) in individuals (aged 45 - 64 years) with borderline hypertension and with low urinary excretion of magnesium and calcium (Rylander et al 2004). In moderately hypercholesterolemic young adults (aged 18 - 40 years), ingestion of a bicarbonated natural mineral water (also rich in sodium, chloride and potassium; 1L/day), for 8 weeks, reduced systolic blood pressure (this alteration was observed after 4-weeks consumption, without significant differences between weeks 4 and 8), fasting serum levels of apolipoprotein B, total cholesterol and LDL-cholesterol as well as the ratios [(total cholesterol)/(HDL-cholesterol)] and [(LDL-cholesterol)/(HDL-cholesterol)] (Pérez-Granados et al 2010). In postmenopausal women, ingestion of the previous natural mineral-rich water (1L/day), for 2 months, increased fasting serum levels of HDL-cholesterol and reduced fasting serum levels of two markers of endothelial dysfunction, glucose, total cholesterol and LDL-cholesterol as well as the ratios [(total cholesterol)/(HDL-cholesterol)] and [(LDL-cholesterol)/(HDL-cholesterol)] (Schoppen et al 2004). Conclusion. Presently, with the increase in MetSyn and type 2 diabetes mellitus, associated with a high consumption of calorie-rich and micronutrient-poor foods, ingestion of natural mineral-rich waters may be beneficial. This effect will be even greater if ingestion of sweetened beverages is replaced by natural mineral-rich waters (Schulze et al 2004; Vartanian et al 2007; Feldeisen et al 2007).
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