Interactions of calcium with other agents (micronutrients, foods):Various nutritive factors can lead to a negative calcium balance, whereby more calcium is excreted through the kidney and intestine than is absorbed – this calcium comes from the bones.For example, certain foods or their ingredients inhibit enteric calcium absorption. These include:
- High-fiber foods, such as wheat bran, flaxseed, wheat germ and legumes.
- Phytic acid (phytates)
- Oxalate
- Phosphates
- Long chain saturated fatty acids
- Tannic acid in coffee and black tea
These foods or food components form a poorly soluble, non-absorbable complex with calcium when absorbed simultaneously inside the intestine and reduce its bioavailability.Medications – glucocorticoids, anticonvulsants, phenytoin – severe diarrhea (diarrhea) and absorption disorders in food intolerances or gastrointestinal diseases also reduce enteral calcium absorption.Increased calcium excretion with urine occurs in:
- Increased caffeine consumption
- High protein intake
- High intake of table salt
- Regular alcohol consumption
- Chronic acidosis
Vitamin D
Vitamin D is essential for optimal calcium absorption.For more information on interactions between vitamin D and calcium, see Vitamin D Interactions.
Sodium
Because of the interdependence between sodium and calcium with respect to their reabsorption in the kidney and the sodium effect on parathyroid hormone (PTH) secretion, increased sodium intake is associated with increased renal loss of calcium. Sodium (Na) and calcium (Ca) are excreted through the kidney in approximately the ratio of 2.3 g Na (equivalent to 6 g salt): 24-40 mg Ca. Sodium is considered a mineral that can lead to bone loss, as much of the calcium retention fluctuations are explained by losses through the urine. In women, each gram of extra sodium can increase the amount of bone loss by 1% per year as excreted calcium is mobilized from bone. Although studies in animals have shown increased bone loss with high sodium intake, no controlled clinical trials have yet been conducted in humans to demonstrate the relationship between sodium intake and bone loss. However, in postmenopausal women, increased urinary sodium excretion – characteristic of increased sodium intake – has been associated with decreased bone mineral density. Potassium
Potassium can also influence calcium metabolism. For example, a high potassium intake prevents increased renal calcium excretion, which is often the result of a high salt intake. Potassium thus promotes calcium retention in the kidney. It is possible that potassium contributes to reduced calcium removal from the bones and thus has a positive effect on bone metabolism. Since potassium can influence the acid-base balance, administration of an alkalizing potassium salt (e.g. potassium bicarbonate or tripotassium citrate) leads to a reduction in renal net acid excretion. This increased the calcium and phosphorus balance and decreased bone resorption, especially in postmenopausal women. To prevent adverse effects on bone metabolism, regardless of potassium intake, neutralization of mild metabolic acidosis resulting from a diet high in animal protein and table salt and low in fruits and vegetables is essential.
Phosphorus
Phosphorus – which is typically found in protein-rich foods – can decrease the excretion of calcium in the urine. At the same time, however, it also increases the calcium content of digestive enzymes, which results in increased calcium loss via defecation. Consequently, due to a concomitant increase in protein intake, phosphorus cannot compensate for the loss of calcium.Today’s increasing intake of phosphorus through soft drinks and food additives could have potential effects on bone health, that is, the risk for osteoporosis (bone loss). A low-calcium, high-phosphorus diet may increase parathyroid hormone (PTH) secretion as much as an exclusively low-calcium diet.Although the impact of high phosphorus intake is currently unclear, the amount of phosphorus-containing soft drinks consumed-instead of milk or other calcium-containing foods-is of concern with respect to bone health in both adolescents and adults.
Zinc and iron
High calcium intake can interfere with the absorption of dietary zinc and iron. It should be noted that especially the simultaneous intake of calcium and the corresponding trace element leads to a reduced absorption via the intestine. Accordingly, the simultaneous intake of calcium and iron can interfere with the absorption of iron from food. Long-term studies with calcium supplements showed no negative effect on the long-term supply of iron to the body. Similarly, the simultaneous intake of calcium and zinc can reduce zinc absorption in the intestine. However, there are also studies that have found no effect on zinc absorption with simultaneous calcium intake. In addition to the timing of intake, the amount also seems to be crucial for an influence.
Protein
Increased protein intake also increases urinary excretion of calcium. Therefore, recommended intake values for calcium are higher in industrialized nations-where protein intake is also generally increased-than in less industrialized nations.Example, United States: recommended daily protein intake is 46 g/day for women and 56 g/day for men; however, protein intake averages 65-70 g/day by women and 90-110 g/day by men. Each additional gram of protein results in an additional loss of 1.75 mg of calcium per day. Since only about 30% of dietary calcium is utilized, each additional gram of protein would require an additional 5.8 mg of calcium to compensate for calcium loss. On the one hand, inadequate protein intake-evidenced by decreased albumin serum levels-is associated with poorer healing of fractures due to osteoporosis; on the other hand, a protein “overabundant” diet-evidenced by increased albumin serum levels-leads to an increased risk of rib fractures.Conclusion!Albumin serum levels have an inverse relation to calcium.
Caffeine
Consumption of large amounts of caffeine briefly increases urinary excretion of calcium. Nevertheless, consumption of 400 mg caffeine/day does not significantly increase calcium excretion over 24 hours.So far, scientific studies contradict each other.On the one hand, accelerated bone loss was found in postmenopausal women based on calcium intake of less than 744 mg/day and concomitant coffee consumption of 2-3 cups/day.On the other hand, another recent study found no relationship between caffeine consumption and bone loss. On average, a 225-ml cup of coffee reduces calcium retention by only 2-3 mg.
