MagnesiumPotassiumCardiovascularDiet & Nutrition

Everything you need to know about magnesium and potassium

Everything you need to know about magnesium and potassium

June 25, 2020

Magnesium: support for a healthy metabolism, the neurological system, and blood pressure control

Magnesium - the second most common deficiency

Magnesium is an essential dietary mineral involved in the proper functioning of various organs, from the nervous, cardiovascular, endocrine and bone systems, to the intracellular production of DNA as a cofactor of more than 300 enzymes. It is the second most abundant electrolyte in the human body, after sodium.

An adequate intake of magnesium can contribute to the reduction of blood pressure, improvement of insulin control, glycemia, and glycated hemoglobin (HbA1c). Magnesium also improves muscle oxygenation and aerobic exercise capacity, reduces symptoms of untreated chronic asthma, increases bone mineral density, improves the neurological symptoms of migraines, and improves sleep quality. For mental health, magnesium is essential in reducing symptoms of anxiety and depression.

Magnesium deficiency is also the second most common deficiency in developed countries after vitamin D. Unfortunately, magnesium deficiency has a clear metabolic impact: it increases blood pressure, reduces insulin sensitivity, and can cause neuronal arousal issues. The symptomatic repercussions of hypomagnesemia only appear when the levels are deficient, so this mineral has not always received the attention it deserves in a clinical context.

99% of magnesium is found within cells. Intracellular magnesium from erythrocytes is the best indicator of hypo/hypermagnesemia. However, presently it is only measured in scientific research and clinical trials.

Only 1% of total body magnesium is found in blood serum. Measuring serum magnesium in a blood test is only a partial indicator as it does not reflect the intracellular reserves. It may also temporarily increase after intake of dietary supplements. The normal range for magnesium is between 0.75 to 0.955 mmol / L.

The Recommended Daily Intake (RDA) for magnesium established by the USDA Dietary Guidelines:

19–30 years: 400 mg (male), 310 mg (female), 350 mg (pregnant), 310 mg (lactating)

31–50 years: 420 mg (man), 320 mg (woman), 360 mg (pregnant), 320 mg (lactating)

Over 51 years: 420 mg (man), 320 mg (woman)

How to reach these levels?

If you follow a varied and balanced diet, magnesium supplementation may not be necessary. However, many people still choose to take magnesium in supplement form. Typically, for the positive effects on blood pressure, sleep quality, insulin sensitivity, and the calming effect, which can help even in depressive symptoms.

Magnesium is present in plants and animal products. Green vegetables, legumes, nuts, and seeds are a dietary source. Processed and refined cereals have low magnesium content, so it is sometimes difficult to achieve a sufficient intake following a traditional diet, rich in derivatives of grains, bread, and little nutritional value packaged foods. Instead, focus on foods with a high magnesium content, such as Basella Alba (Malabar spinach or Chinese spinach), some species of mushrooms and seeds, and royal jelly.

You can also find relatively high amounts in almonds, cashews, spinach, broccoli, quinoa, avocado, tofu, soy milk, legumes (especially black beans), edamame.

Vegetables with a high fibre content will generally provide magnesium. Approximately 20% -30% of the mineral consumed in the diet will be absorbed, with more favourable percentages in the case of green vegetables (40-60%). Mineral water is a valuable source of magnesium: the ranges between different brands vary from 1 mg/L to more than 120 mg/L, so it is possible to reinforce the intake with mineral water or magnesium fortified water.

How about supplementation? The standard dose of a magnesium supplement is between 200-400mg. There are numerous formulations: magnesium citrate, magnesium lactate, magnesium gluconate, and sodium magnesium are those with the best bioavailability and tolerance. When magnesium is not absorbed effectively in the intestine, it can cause gastrointestinal problems.

With a pre-existing magnesium deficiency, if high-dose intake is required, magnesium glycinate or magnesium gluconate (high-load temporary supplementation) is recommended.

The intestinal absorption of magnesium is very tightly regulated. Paracellular and transcellular mechanisms of intestinal enterocytes are responsible for transporting only the amount of magnesium that the body needs— more in periods of deficiency and less in periods of adequate reserves.

Potassium: the key to optimal cardiovascular function

Potassium is an essential mineral in the human diet found in green vegetables, fruits, and legumes. Its best known physiological effect is that it acts inversely to sodium: diets rich in potassium are associated with better control of blood pressure. Supplementation, or increased potassium intake, may be indicated to reduce the risk of heart attack, primarily through dietary sources (the effect is not dose-dependent, both small and significant increases in intake seem to confer a protective effect).

However, there is some controversy about potassium in the supplement world, given that high doses or accidental potassium intake in powder form can cause significant electrolyte disturbances and even cardiac arrhythmias. In a clinical context, monitoring of sodium and potassium is essential in hospitalised patients for precisely this reason. Various drugs can affect kidney function, hyperglycemia, and kidney disease and increase the risk of hyperkalemia. Supplementing through diet, however, does not cause this situation, since intestinal absorption takes longer even when consuming large amounts of vegetables rich in potassium and fibre.

Serum potassium levels are tightly regulated by the renal system, ranging from 3.5 to 5.3mEq/L in adults. This range is kept constant thanks to the potassium reserves in the cells, matching the amount ingested with the amount that is eliminated. Since potassium deficiency is rare, "recommended daily amounts" (RDA) have not been established for this mineral in the past. This requirement has been revised in the new nutritional guidelines, with the daily "Adequate Intake" of potassium in adults standing at around 3400mg in men and 2600mg in women, through dietary sources.

Selling supplements with more than 99mg of potassium per capsule is not common because of the cardiac risks associated with accidental overdoses. From epidemiological and clinical supplement studies, an appropriate range appears to be between 1600 to 2000mg (40 to 50 milliequivalents) in adults, per day. If it is difficult for us to achieve adequate levels through dietary intake, we could resort to supplements (but with due caution to separate the consumption correctly throughout the day!).

How to reach these levels?

The list of foods that contain potassium in significant amounts is extensive. It includes pumpkin, spinach, avocado, lentils and beans, peas, edamame, watermelon, coconut water, brussels sprouts, chard, broccoli, mushrooms, cucumbers, bananas and some dried fruits such as prunes, raisins, and dates.

It is preferable to use green leafy vegetables such as spinach, broccoli, brussels sprouts, or avocado or mushrooms since they are satiating foods with a low-calorie density. Bananas are "famous" for potassium content (358 mg per 100g), but many of the foods listed above contain a higher relative amount by weight.

Since nuts, legumes and bananas can be high in simple carbohydrates (sugars) and, comparatively, in calories, if you suffer from insulin resistance problems (prediabetes or diabetes), it may be preferable to opt for green, leafy vegetables as a dietary source.

Finding high-dose supplements can be difficult, as manufacturers try to limit overdose for the heart risks described above. You can buy salt substitutes (potassium chloride) in specialized stores, but its use is recommended only sporadically and always accompanying main meals.

The risk of hyperkalemia of various supplementation doses has been evaluated. We observe that, in a range between 1,950-2,925 mg/day, when taken in divided doses, blood potassium levels do not increase in a dose-dependent manner, and no adverse reactions or side effects have been reported. In general, therefore, it is better to resort to dietary sources to achieve the recommended intake of potassium and, in the case of taking supplements, take moderate doses (not exceeding 1000mg daily, which seems to provide all the cardiovascular benefits) and spread throughout the day, with meals.

Finally, it is worth mentioning that both magnesium and potassium are two key electrolytes in the initiation and maintenance of a low carbohydrate diet and, in general, any radical dietary change that implies a high caloric restriction (and, therefore, alteration factors that depend on insulin signalling pathways, such as sodium and potassium regulation).

In the ketogenic or low carbohydrate diet, or "Palaeolithic" or vegetarian diets, it is crucial to maintain adequate sodium, magnesium, and potassium levels. It is of particular interest in the initial stages of adaptation to the new dietary regimen, due to the large amount of fluid that can be lost: using a little more salt in meals than usual, increasing the intake of low-carbohydrate content, green, leafy vegetables and, if necessary, supplement magnesium (between 200-400mg / day) and potassium (500-1000mg / day).

Potassium also has the added benefit of reducing the amount of calcium excreted in the urine, which has been proposed as one of the reasons why potassium supplementation could help prevent kidney stone formation (as shown in long-term clinical trials evaluating children with a classic ketogenic diet (4:1) as an antiepileptic treatment).

NOTICE: This informative article is based on the bibliographic sources cited below and has been reviewed by the Melio Reviewers Committee. All content is valid as of the date of publication, but may not include newer information. This blog is presented for informational purposes only and does not constitute the practice of Medicine, Nursing or other professional health services, including the provision of medical advice, and therefore does not constitute a doctor-patient relationship. The use of information or materials linked from this blog are under the responsibility of the user. The content of this blog is not intended as a substitute for medical advice, diagnosis or treatment.

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Ahmed, F. and A. J. M. S. Mohammed (2019). "Magnesium: The Forgotten Electrolyte—A Review on Hypomagnesemia." 7(4): 56. Curhan, G. C., et al. (1993). "A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones." 328(12): 833-838.

Gebhardt, S., et al. (2008). "USDA national nutrient database for standard reference, release 21."

He, F. J. and G. A. J. B. MacGregor (2001). "Beneficial effects of potassium." 323(7311): 497-501.

Lemann, J., et al. (1991). "Potassium administration reduces and potassium deprivation increases urinary calcium excretion in healthy adults: Erratum." 40: 388.

Malon, A., et al. (2004). "Ionized magnesium in erythrocytes—the best magnesium parameter to observe hypo-or hypermagnesemia." 349(1-2): 67-73.

McNally, M. A., et al. (2009). "Empiric use of potassium citrate reduces kidney-stone incidence with the ketogenic diet." 124(2): e300-e304. Simon, L. V. and M. W. Farrell (2018). Hyperkalemia. StatPearls [Internet], StatPearls Publishing.

Viera, A. J. and N. J. A. f. p. Wouk (2015). "Potassium Disorders: Hypokalemia and Hyperkalemia." 92(6).