Dear Dietitian,

I take a magnesium supplement and sometimes soak in Epsom salt for joint pain. I read an article that said the only way the body can absorb magnesium is through the skin. Is that true? Should I buy a magnesium cream instead of a dietary supplement?

John

Dear John, 

There’s nothing like a warm, relaxing Epsom salt (magnesium sulfate) bath after a good work-out. Magnesium is a mineral needed by the body for several functions, including muscle and nerve function, bone mineralization, and building protein. One of magnesium’s most common uses is to relieve constipation. Magnesium is in every cell and has a vital role in energy metabolism. It also has a role in oral health by building strong tooth enamel. Food sources of the mineral include nuts, legumes, whole grains, dark green vegetables, seafood, and chocolate.

Magnesium requirements vary by age. Adult men need 420 mg per day, while women need 320 mg daily. Reported magnesium deficiencies are rare and typically do not happen without disease. Magnesium deficiency occurs in alcohol abuse, malnutrition, kidney or endocrine problems, and illnesses that cause prolonged diarrhea and vomiting. A severe deficiency will cause tetany, commonly known as lockjaw.

Certain medications may contribute to a lower magnesium level. These drugs include diuretics, such as furosemide, and proton-pump inhibitors like omeprazole and lansoprazole. If you are taking any of these medications, ask your doctor if you need a magnesium supplement.

As with any mineral, toxic doses are possible. Magnesium toxicity is rare and will not occur from getting too much of the mineral in your diet. Extreme doses can be taken intravenously. Symptoms of toxicity include low blood pressure, vomiting, and lethargy. If left untreated, toxic levels will cause difficulty breathing, irregular heartbeat, and cardiac arrest.

The kidneys play a significant role in keeping magnesium levels normal. If dietary intake is high, the kidneys will excrete excess magnesium in the urine. With low magnesium intake, the kidneys conserve the nutrient very efficiently. Those with chronic kidney disease have a less effective monitoring process and may retain excess levels of magnesium. 

As for absorption, any nutrient, whether it is a vitamin, mineral, protein, or water, is best absorbed when taken orally and processed by the gastrointestinal (GI) tract. Digestion and nutrient absorption are two of the primary responsibilities of the GI system. Intravenous replacement is sometimes used in the hospital setting to increase magnesium levels rapidly.

In the case of absorption of magnesium cream, there are few studies on the subject. Some small studies have shown an increase in magnesium levels when using cream. It is possible that magnesium enters the skin, travels the lymphatic system while bypassing the GI tract, and finally reaches the circulatory system. Epsom salt baths may work by this process, or it may be the warm water in the soak that alleviates muscle and joint discomfort. Some experts do not accept the skin method as scientifically-proven. Others warn against its use, since a magnesium deficiency can occur if the mineral is not adequately absorbed. 

Another factor to consider when purchasing a magnesium supplement is cost. Magnesium gels tend to be more expensive, so expect to pay about eighteen dollars for an eight-ounce container. Oral magnesium supplements cost about ten dollars for 100 tablets, although prices vary considerably. It always pays to be an informed consumer.

Until next time, be healthy!

Dear Dietitian