The upper daily intake limit of calcium is 2,500 mg (19–50 years old) or 2,000 mg (51 years and older).
Calcium Supplements
• Types. Calcium supplements come in different chemical formulations, including calcium carbonate, calcium citrate, calcium malate, calcium lactate, calcium gluconate, and the like. Among them, calcium carbonate is the least expensive—this is the form found in oyster shells and coral. It is easier for the intestines to absorb calcium citrate and calcium malate compared to calcium carbonate. Owing to high molecule weights, calcium lactate and calcium gluconate supplements are mainly available in large tablet sizes, which may contain less calcium per tablet.
• Dosage. Calcium contents in calcium supplements often are not clearly stated on the label. For instance, based on their weights, calcium carbonate, calcium malate, and calcium gluconate contain only 40%, 21%, and 9% calcium, respectively. A 1-gram tablet of a calcium gluconate supplement may have only 90 mg of calcium. Read the label carefully for the calcium content of these products when purchasing.
• Preteen and teenage girls. During growth and development, girls aged 9–18 should take 500 mg of calcium and 800 IU of vitamin D daily.
• Women. Calcium supplementation can attenuate premenopausal syndromes, including mood swings, headaches, overeating, and bloating. It is recommended that premenopausal women take 1 g of calcium daily for three days before menstruation.
• Bone fractures. Calcium plus vitamin D supplements prevent bone fractures. It is recommended that postmenopausal women take 500 mg of calcium and 400 IU of vitamin D daily to curtail the risk of bone fractures.
• Hypertension. Calcium deficiency elevates the risk of hypertension. Calcium supplementation lowers systolic and diastolic pressure in hypertensive patients.
• Life-span. Taking calcium supplements may extend the life-span. Studies from Canada have shown that postmenopausal women who took calcium supplements at a daily dose of 1 g for 10 years had a reduced rate of death from cardiovascular diseases.
• Cholesterol. Taking daily supplements of calcium at a dose of 1 g for one year raises “good” cholesterol (HDL) and lowers “bad” cholesterol (LDL) in postmenopausal women.
Safety Issues
• Overdose. Daily supplements of calcium at doses greater than 1,500 mg may increase the risk of prostate cancer and heart disease. On the other hand, calcium insufficiency also adds to the risk of prostate cancer.
• Vitamin D. Vitamin D enhances calcium absorption in the intestines. It is beneficial to take calcium and vitamin D supplements together. A dose of 500 mg of calcium is absorbed very efficiently by the intestines. If a daily dose of 1,000 mg of calcium is needed, you may take 500 mg twice a day.
• Diet. High-sodium and protein-rich diets may trigger overexcretion of calcium in the urine. People who enjoy salty and meaty meals need to be cautious about potential calcium deficiency.
What Types of Drugs May Interact with Calcium?
• Diuretics. Diuretic drugs may enhance renal absorption of calcium, leading to problems associated with high blood calcium levels.
• Digoxin. Heart failure patients who take digoxin together with calcium supplements may exacerbate the risk of atrial fibrillation.
• Antibiotics. Taking calcium supplements may interfere with the absorption of tetracycline and other antibiotics by the intestines.
• Other medications and supplements. Antacid drugs, corticosteroids, heparin, iron, manganese, and chromium all lower the absorption of calcium by the intestines.
• Diabetes. Metformin interferes with the absorption of vitamin B12 by the intestines in type 2 diabetes patients. Calcium supplementation improves the absorption of vitamin B12. The suggested daily dose is 1 g of calcium.
Potassium is an essential element. On average, the human body contains about 120 g of potassium, exclusively in the form of potassium ions. Potassium ions are the most abundant cations (or positively charged ions) in the body, followed by sodium ions. Potassium ions are stored inside the cell, while sodium ions are stored outside the cell. Potassium concentration inside the cell is 30 times higher than potassium concentration outside the cell, and sodium concentration outside the cell is 10 times higher than sodium concentration inside the cell. Owing to these concentration gradients of potassium and sodium, each cell holds a tiny electric field and acts like a small battery, negatively charged inside while positively charged outside. The human body comprises 37.2 trillion cells, so we have 37.2 trillion small batteries in the body. About 40% of our daily food intake is used to recharge all these tiny batteries. A healthy body is sustained only when all of them are fully charged. The importance of potassium to human health is beyond description.
What Are the Major Functions of Potassium Ion?
• Membrane potential. All cellular membranes, particularly neurons, hold a membrane potential with negatively charged inside and positively charged outside. Membrane potential is about 70 microvolts, through which the semipermeability of the cellular membrane is established. Potassium is actively pumped into the cell, while sodium is actively pumped out of the cell. Potassium and sodium concentration gradients establish the membrane potential, and it is crucial for the existence of all living beings. If potassium and sodium concentration gradients were abolished, the membrane potential would be lost, leading to instant cell death.
• Cofactor. Potassium ions serve as cofactors for many enzymes, among which the most important enzyme is sodium-potassium ATPase. Sodium-potassium ATPase is a membrane protein that can convert ATP to ADP and release its energy for muscle contraction and the like.
• Other functions. Other cellular functions of potassium include blood pressure control and regulation, the peristaltic movement of the intestines, acid-alkaline balance, and glucose and insulin metabolism.
What Are the Symptoms of Potassium Deficiency?
• Potassium deficiency precipitates hypokalemia, characterized by weakness, fatigue, numbness in the extremities, bloating, nausea and vomiting, constipation, palpitations, and even mental disorders, such as depression, psychosis, and
