How Much Magnesium Is Enough: RDA and EAR
The proposed normal range for serum magnesium is approximately 1.7 to 2.2 mg/dL.49 The RDA (recommended daily allowance) and EAR (estimated average requirement) to maintain healthy levels of magnesium vary based on age, sex, and reproductive status (Table 2).50-52
Table 2. Estimated average requirements (EAR) and recommended daily allowances (RDA) for magnesium intake in adults.50-52
|Age (years)||EAR (mg/day)||RDA (mg/day)|
The Problem: Insufficient Dietary Magnesium Intake
With declining nutrient content in foods and broad consumption of SAD-style diets, deficiencies in essential nutrients such as magnesium have become extremely common. An analysis of 2005-2006 NHANES data identified dietary magnesium intake below EAR (estimated average requirement) in 48% of 8437 participants.6 In this study, about 60% of surveyed adults did not consume the established RDA (recommended daily allowance) for magnesium. A diet-modeling study based on 8944 participants in NHANES (2007-2010) revealed that the percentage of individuals consuming below the EAR for magnesium ranged from 51.7%-88.5% for adult males and 34.5%-75.8% for adult women.5 Accordingly, the 2015-2020 Dietary Guidelines for Americans designate magnesium as an under-consumed nutrient relative to the EAR in the diets of both males and females aged 2 years of age and older.52
Improving Dietary Magnesium Intake: Whole Foods
Dietary sources of magnesium include many whole foods, such as nuts, seeds, legumes, whole-grain cereals, and many vegetables (Table 3).53-57 Conversely, consumption of processed foods, sugars, saturated fats, and refined grains – all of which are common in the SAD – is associated with reduced intake of magnesium and other essential nutrients.58
Table 3. Dietary sources of magnesium.53
|Food group||Examples||Mg content (mg/100g)|
|Nuts and seeds||Pumpkin seeds||592|
|Potatoes with skin||43|
|Whole grains||Buckwheat flour||251|
In a worrying trend, studies have described declining concentrations of micronutrients in food since the first half of the 20th century. For example, investigators have identified magnesium reductions of 4%-8% in beef, 4% in chicken, 38% in cheddar cheese, 70% in parmesan cheese, 21% in whole milk, and 24% in vegetables over decades.59 The magnesium content of wheat has dropped almost 20% since the 1960s, likely due to changes in the soil (e.g., acidification, mineral depletion) and modern cultivation practices (e.g., selective breeding, chemical fertilizers).60 The processing and refinement of food leads to further substantial losses of magnesium. In fact, most processed foods and highly refined grains (e.g., white flour, sugar) are essentially devoid of magnesium.
An analysis of NHANES data (2007-2010) suggested that even with adequate dairy intake (a common source of magnesium), magnesium deficiencies would remain highly prevalent in Americans (34%-75% of males, 17%-51% of females).5
Magnesium levels vary by type of plant, cultivar, and plant anatomy. Magnesium is mobile in the phloem and can be found in high concentrations in rapidly growing structures with good access to phloem, such as roots, seeds, tubers, and fruit. Some species with higher concentrations of magnesium in the leaves include beets, chard, and spinach.61 Magnesium concentrations also vary by cultivar. One review identified magnesium levels ranging from 45.8-69.3 mg/100 g across varieties of kale and 8.7-12.3 mg/100 g among types of carrots.61
Given the wide range of magnesium levels within and between plants, consuming a variety of plants may be the best strategy to optimize dietary magnesium intake.
The Benefits of Magnesium Supplementation
With the declining levels of magnesium in available foods, many people may be challenged to maintain adequate magnesium levels through diet alone. Magnesium supplements are another option to support healthy magnesium status. Compared to food alone, the addition of dietary supplements significantly increases intake of nutrients, including magnesium, and reduces nutrient inadequacies in adults.62
The benefits of magnesium supplementation have been widely demonstrated. Several such studies are illustrated in Table 1. Additional studies have linked magnesium supplementation to reduced stress and depressive symptoms. For example, a study from France evaluated the effect of supplementation with magnesium, probiotics, and vitamins in 242 subjects with psychological stress.63 Following 1 month of supplementation, measures of subjects’ psychological stress decreased significantly (P<0.0001); fatigue scores also decreased significantly (P<0.0001). An open-label, randomized study evaluated the effect of magnesium supplementation in 126 adults with mild-to-moderate depression.64 After 6 weeks of magnesium chloride supplementation, depressive symptoms improved significantly over baseline (6.0 point improvement in Patient Health Questionnaire-9 scores, P<0.001). Anxiety scores also improved significantly. The supplement was well tolerated, and 61% of participants said they would use magnesium in the future.
Many people are in need of some level of magnesium supplementation. These deficits are illustrated in Table 4, which shows the mean daily intake of magnesium in the 2011-2012 NHANES survey compared to RDA.65 The addition of a supplement containing 100mg dietary magnesium would bring the mean magnesium intake to within the RDA values for both gender for all age brackets.
Table 4. Magnesium intake from food and beverages compared to RDA and the impact of a 100 mg/day magnesium supplement. Data from the 2011-2012 NHANES survey.65
|Gender||Age (years)||Daily intake (mg/day)||RDA (mg/day)||Mg deficit (mg)||Difference with 100 mg/day supplement (mg)|
Magnesium is an essential nutrient for human health. Deficiencies in magnesium increase risk for serious chronic diseases, whereas increased intake through improved diet and/or supplementation can improve health status and reduce disease risk. Unfortunately, current evidence indicates that half or more of Americans currently have some degree of subclinical magnesium deficiency. Increasing magnesium intake requires greater consumption of whole foods (unrefined grains, vegetables, fruits, nuts) and reduced intake of refined or processed foods. For many people, the addition of a magnesium supplement may be required to replete magnesium stores and maintain healthy magnesium levels over the long term.