Learning objectives
- •
Signs and symptoms of magnesium deficiency.
- •
Identifying individuals at risk of magnesium deficiency.
- •
Impact of magnesium deficiency.
The case study
Reason for seeking medical help
Mrs. JL is experiencing nausea and vomiting for the past 3 days, as well as intermittent muscle cramps. She is known to have osteoporosis as evidenced by a T-score of −2.5 in her left femoral neck and has been on alendronate for about 2 years.
Past medical/surgical history
- •
Surgical menopause age 48; 3 years of HRT.
- •
Fractured right radius as a child skateboarding.
Personal habits
- •
Physically active: walks her two dogs daily.
- •
Babysits her 4-year-old grandson 3 days a week.
- •
No cigarette smoking.
- •
Drinks one cup of coffee daily, and two glasses of sweet tea.
- •
Drinks two glasses of almond milk, one cup of yogurt daily.
Medication
- •
Alendronate 70 mg weekly.
- •
Multivitamin daily.
- •
Fish oil.
- •
Vitamin D3 1000 units daily.
Family history
- •
Negative for osteoporosis.
Clinical examination
- •
Weight: 118 lbs, height 66″.
Laboratory investigations
- •
Serum 25-hydroxy-vitamin D: 30 ng/mL.
- •
Calcium 8.9 mg/dL.
- •
Magnesium: 0.65 mmol/L.
- •
Comprehensive metabolic profile: within normal limits.
Multiple choice questions
- 1.
Magnesium homeostasis:
- A.
A cause-and-effect relationship between dietary magnesium intake and osteoporosis has not been established.
- B.
A tight control of magnesium homeostasis is essential for bone health.
- C.
Lower blood levels of magnesium are associated with osteoporosis.
- D.
B and C.
- E.
All of the above.
Correct answer: D
Comment:
Several studies have shown that about a third of patients with osteoporosis have hypomagnesaemia, and that about 20% of patients with osteoporosis constantly consume diets low in magnesium. Total magnesium in an adult body ranges from 20 to 28 g: approximately 60% in bones, 39% in intracellular compartments, and about 1% in extracellular fluids.
A cause/effect relationship between dietary magnesium intake and osteoporosis has been established. Magnesium is found in many foods in varying concentrations. Its concentration in leafy vegetables is 30–60 mg/100 g. Larger quantities are present in legumes (80–170 mg/100 g), nuts (130–264 mg/100), and whole grain in wheat bran (up to 550 mg/100 g).
As much as 80% of the magnesium in food is removed during refining treatments; for instance, white bread contains only 15 mg/100 g. Coffee contains about 80 mg/100 g. Dried fruit, potatoes, meat, fish, and milk are less rich in magnesium. The magnesium content of bottled water varies between 1 and 109 mg/mL, with an average of 15 mg/mL.
The bioavailability of magnesium also varies according to other specific components of the diet such as phytates, calcium, phosphorus, and long-chain fatty acids which may reduce magnesium gastrointestinal absorption. Cooking, also, may reduce the bioavailability of magnesium.
Magnesium can be taken orally as citrate, carbonate, or oxide, in doses between 250 and 1800 mg daily. An increase in bone mineral density and a reduction in fracture risk have been recorded in individuals taking magnesium supplements.
- A.
- 2.
The effects of magnesium deficiency include:
- A.
Increased bone fragility.
- B.
Impaired vitamin D synthesis and activation.
- C.
Impaired neurotransmission.
- D.
All of the above.
- E.
None of the above.
Correct answer: D
Comment:
Magnesium contributes to a number of body functions, including a direct effect on bone fragility, vitamin D synthesis, electrolyte balance, neurotransmission, and muscle contraction, including heart muscles, cell division, protein synthesis, and maintenance of bones and teeth. Magnesium is also an essential cofactor for vitamin D synthesis and activation which in turn may increase intestinal magnesium absorption.
An important issue to consider is that routinely measured serum magnesium levels do not always accurately reflect the total body magnesium status, so a patient with a “normal serum magnesium” level may in fact have magnesium deficiency.
- A.
- 3.
Symptoms of magnesium deficiency include:
- A.
Nausea/vomiting.
- B.
Fatigue.
- C.
Seizures.
- D.
Muscle cramps.
- E.
All of the above.
Correct answer: E
Comment:
The first signs of hypomagnesemia are nausea, vomiting, and fatigue. JL presents with nausea and vomiting. As the deficiency progresses, numbness, muscle cramps, and seizure occur and eventually, abnormal heart rhythms can develop.
- A.
- 4.
Individuals at risk of magnesium deficiency include those with:
- A.
Crohn’s disease.
- B.
Type II diabetes mellitus.
- C.
Alcoholic dependency.
- D.
Older adults.
- E.
All of the above.
Correct answer: E
Comment:
Celiac and Crohn’s disease can lead to a decrease in magnesium levels due to malabsorption and diarrhea. Diabetes mellitus can cause an increase in urinary excretion of magnesium. Alcohol dependence and hypomagnesemia can develop as a result of the combination of gastrointestinal issues, such as diarrhea and overall poor nutritional status. In the case of older adults, they tend to consume less foods that contain magnesium and have a decreased ability to absorb the magnesium they consume. In JL’s case, her main risk factor is her age, as she does not have Crohn’s disease, type II diabetes, or alcohol dependency.
- A.
- 5.
The best course of action with JL is to:
- A.
Supplement magnesium.
- B.
Increase her dietary intake of magnesium.
- C.
Supplement magnesium and potassium.
- D.
Supplement magnesium, potassium, and calcium.
- E.
A and B.
Correct answer: E
Comment:
JL should be educated about food sources that contain magnesium and her Recommended Daily Allowance (RDA) of magnesium. If she is already eating a diet rich in these foods, she may have a decreased ability to absorb magnesium and would benefit from magnesium supplementation.
- A.
- 6.
JL is on a bisphosphonate. Important teaching regarding magnesium supplementation include:
- A.
Taking the bisphosphonate with the magnesium supplement at the same time to increase the absorption of both.
- B.
Taking the magnesium supplement at least 2 h after her bisphosphonate.
- C.
Taking the magnesium supplement 30 min after her bisphosphonate.
- D.
Stopping the bisphosphonate and prescribe zoledronic acid instead.
- E.
Taking the magnesium supplement 30 min before the bisphosphonate.
Correct answer: B
Comment:
The intake of magnesium supplement should be separated from the bisphosphonate by at least 2 h to prevent a decrease in the amount of bisphosphonate absorbed. The bisphosphonate should be taken first while fasting.
- A.
- 7.
Foods that contain magnesium include:
- A.
Pumpkin seeds.
- B.
Peanut butter.
- C.
Avocado.
- D.
Yogurt.
- E.
All of the above.
Correct answer: E
Comment:
Magnesium is found in a wide variety of foods. Pumpkin and chia seeds have the largest amount per serving. Magnesium can be found in meat; vegetables such as spinach, broccoli; fruits; and various nuts. The recommended daily allowance of magnesium is 320 mg for women older than 51 years old, as is JL’s case.
- A.
- 8.
Magnesium deficiency can result in:
- A.
Osteoporosis.
- B.
Sarcopenia.
- C.
Cardiovascular disease.
- D.
Kidney disease.
- E.
A, B, and C.
Correct answer: E
Comment:
Magnesium deficiency is intertwined with all three diseases: osteoporosis, sarcopenia, and cardiovascular diseases. Sarcopenia is the loss of muscle mass and function. Magnesium is involved in muscle contractions as well as bone formation. Magnesium supplementation can decrease blood pressure which is a risk factor for patients with cardiovascular diseases.
Magnesium levels can be measured in a variety of ways. With only about 1% of magnesium residing in serum levels, sometimes a magnesium tolerance test is used to assess magnesium status. This involves infusing magnesium and then measuring urinary output and is far more invasive. Magnesium status should be evaluated clinically as well as by laboratory studies. In JL’s case, she exhibits both clinical symptoms and has a low magnesium level.
- A.
- 9.
Magnesium is closely linked with:
- A.
Calcium.
- B.
Vitamin D.
- C.
PTH.
- D.
A and B.
- E.
All of the above.
Correct answer: E
Comment:
Magnesium is needed for calcium and vitamin D metabolism. Calcium levels are decreased with insufficient magnesium intake. When magnesium levels decrease, the body tries to compensate by increasing PTH levels to maintain homeostasis.
- A.
- 10.
Magnesium deficiency can lead to osteoporosis by:
- A.
Increasing bone turnover.
- B.
Affecting calcium, PTH, and vitamin D.
- C.
Inducing inflammation and bone remodeling.
- D.
Inducing endothelial dysfunction.
- E.
All of the above.
Correct answer: E
Comment:
Magnesium affects the body’s homeostasis by all of the processes mentioned before and can lead to bone mineral density loss if not corrected. Serum levels of magnesium are not an accurate picture of a person’s magnesium status as they consider neither intracellular magnesium nor magnesium in the bones.
Other methods of measuring magnesium include ionized magnesium, magnesium tolerance test, and measuring magnesium levels in the saliva and urine.
- A.
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