Magnesium (Mg) is the fourth most abundant mineral in the body, being essential for life. It takes action as a cofactor of enzymes involved in glucose metabolism, protein production and nucleic acid synthesis [1, 2]. Mg balance is regulated by an interaction between intake, intestinal absorption, renal excretion and exchange from bone (not completely available in cases of Mg deprivation) . Because of the daily loss of Mg in faeces, urine and sweat, humans require a continuous supply from exogenous sources by dietary intake – recommended dietary allowance of 420mg/day for adult men and 320mg/day for adult women [3, 4]. In certain periods of life, Mg intake needs are higher (as in pregnancy and lactation) and can vary across age and sex.
Mg deficiency is relatively common in general population [5, 6] and the primary cause of hypomagnesemia is often insufficient dietary intake. In Europe and in the United States, due to the “western” dietary pattern, the daily allowance of Mg is not accomplished in a large proportion of people . Also, the methods of refining and process foods tend to diminish Mg content .
Dietary Mg is mostly absorbed by the duodenum and jejunum via passive paracellular transport. The intestinal absorption is not directly proportional to Mg intake, but depends on body’s Mg status . Serum or plasma Mg concentration is the most common used biomarker to assess Mg metabolism abnormalities in clinical practice (reflecting not only the dietary intake, but also the intestinal absorption, renal reabsorption and excretion, and hormone regulation) . The normal range of serum Mg is 0.76–1.15 mmol/L, approximately 1.52–2.30 mEq/L . Although hypomagnesemia is not always present in cases of Mg deficiency, it is usually indicative of an important systemic Mg deficiency .
Literature suggests an association between Mg and cardiovascular risk. Mg dietary intake is inversely associated with the incidence of several cardio-metabolic conditions, namely type 2 diabetes mellitus (T2DM) [2, 4, 19, 11–18]. This finding suggests that increased consumption of Mg-rich foods or Mg supplements may reduce the risk of T2DM [13–16, 19]. Some authors suggest that Mg supplementation could improve glycaemic control in T2DM patients [20–22], while, at the same time, other studies show no significant effects of Mg supplementation on T2DM [23, 24]. On the other hand, the relation between Mg serum levels and T2DM is more intriguing [10, 25]. T2DM is often accompanied by hypomagnesemia, especially in older patients, with poorly controlled glycaemic profiles, with longer duration of the disease or presence of micro or macrovascular chronic complication [26–30]. The incidence of hypomagnesemia in patients with T2DM ranges from 13.5 to 47.7% compared with 2.5 to 15% in healthy control subjects [23, 31, 32]. In a 2017 study, authors observed a prevalence of 30.6% in T2DM patients .
T2DM and obesity are increasingly common and major global health problems . Obese adults are at increased risk for developing major diseases, such as T2DM, coronary artery disease, stroke, non-alcoholic fatty liver disease, depression and certain cancers [35, 36]. Bariatric surgery (BS) remains the most effective treatment in severe obesity  and also provides T2DM remission or improvement of glucometabolic status (which became a recommendation to BS in individuals unable to achieve adequate glycaemic control with oral or injectable medications) . After Roux-en-Y Gastric Bypass (RYGB), remission rates between 43.2% and 84% have been reported, with heterogeneity regarding the definition of diabetes remission . Several studies have tried to identify predictive factors for T2DM remission after BS. Due to the previously described relationship between Mg and T2DM, the post-bariatric assessment of Mg status has been evaluated recently , and patients with T2DM that achieved remission after RYGB had higher Mg serum values when compared to patients that didn’t achieve remission.
After bariatric surgery, micronutrient deficiencies are one of the most common and compelling problems and supplementation is recommended . On the other hand, the majority of studies show a decrease in hypomagnesemia in post-bariatric patients [42–48].
As mentioned previously, in general, higher Mg intake is associated with lower risk of T2DM and better glycaemic control and, on the other hand, hypomagnesemia occurs, typically, in patients with poor glycaemic control. Taking into account that numerous micronutrient deficiencies are more common after BS, the aim of this study is to evaluate the association between Mg supplementation post-BS and Mg serum levels, prior and post-surgery, with T2DM glucometabolic status and remission. To the best of our knowledge, this is the first study aiming to assess the relationship between Mg supplementation post-BS and T2DM glycaemic control and remission in post-bariatric patients.