Magnesium is a critical mineral that is involved in over 600 enzymatic reactions, including those important for brain, heart, and skeletal muscle functions.1 Interestingly, about 60% of Americans are deficient in magnesium, including up to 60% of patients who are critically ill.

In regard to cancer, magnesium intake has been associated with the incidence of some cancers and has been studied as a protective agent against chemotherapy-induced nephrotoxicity and neurotoxicity.

Cancer Risk

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Colorectal Cancer

Several studies have demonstrated an association between high magnesium intake and reduced risk of colorectal cancer (CRC).

An analysis of the prospective, Swedish Mammography Cohort, evaluated 61,433 women aged 40 to 75 without a history of cancer for a mean follow-up of 14.8 years.2 The highest quintile of magnesium intake was associated with a significantly lower risk of CRC compared with the lowest quintile (multivariate rate ratio [RR], 0.59; 95% CI, 0.40-0.87). This benefit was observed for both colon (RR, 0.66; 95% CI, 0.41-1.07) and rectal (RR, 0.45; 95% CI, 0.22-0.89) cancers.

A case-control study evaluated 2204 subjects from the Tennessee Colorectal Polyp Study, which demonstrated that increasing total magnesium intake was significantly associated with decreasing risk of CRC (highest tertile odds ratio [OR], 0.54; 95% CI, 0.36-0.82; P < .01).3 The highest tertile of dietary magnesium intake (>298 mg/day) was significantly associated with reduced risk of CRC in an age-adjusted model (OR, 0.75; 95% CI, 0.60-0.95; P = .02).

A study of 140,601 postmenopausal women from the Women’s Health Initiative with an mean follow-up of 13 years demonstrated a significant reduction in CRC risk with the highest quintile of total magnesium intake compared with the lowest quintile of magnesium intake (hazard ratio [HR], 0.79; 95% CI, 0.67-0.94; P < .0001).4 The benefit was driven by colon cancer (HR, 0.80; 95% CI, 0.66-0.97; P < .0001), with a trend for rectal cancer (HR, 0.76; 95% CI, 0.51-1.13; P < .001).

Another study, however, found no association between magnesium intake and incidence of CRC.

A study with a mean follow-up of 11 years of the Women’s Health Study cohort demonstrated no association between total magnesium intake and CRC incidence, even when potentially confounding factors such as body mass index, physical activity, or smoking status, were considered.5

Pancreatic Cancer

A study of 66,806 subjects aged 50 to 76 at baseline from the Vitamins and Lifestyle cohort evaluated magnesium intake and the incidence of pancreatic cancer during a mean follow-up of 6.8 years.6 Subjects with magnesium intake below the recommended dietary allowance were more likely to develop pancreatic cancer, particularly in those whose intake was less than 75% of the recommended dietary allowance (HR, 1.76; 95% CI, 1.04-2.96). In this study, a 100 mg/day decrease in magnesium intake resulted in a 24% increase in risk of pancreatic cancer (HR, 1.24; 95% CI, 1.02-1.50; P = .03).