Factors Affecting Calcium Absorption and Excretion

Calcium absorption is the amount your body absorbs from your digestive tract into your body’s circulation. Calcium absorption can be affected by your body’s status of calcium and vitamin D, age, pregnancy and plant substances in your diet.

The amount of calcium consumed at one time can also affect absorption. In other words, calcium absorption decreases as the amount of calcium consumption increases in a meal. Thus, spreading consumption of calcium throughout your day is best.

Other factors playing important roles in calcium absorption are:

  • Age: Net calcium absorption can be as high as 60% in infants and young children, when the body needs calcium to build strong bones. Absorption slowly decreases to 15-20% in adulthood and even more as one ages. Because calcium absorption declines with age, recommendations for dietary intake of calcium are higher for adults ages 51 and over.
  • Vitamin D helps improve calcium absorption. Your body can obtain vitamin D from food and it can also make vitamin D when your skin is exposed to sunlight. Thus, adequate vitamin D intake from food and sun exposure is essential.
  • Plant substances containing phytic acid and oxalic acid, which are found naturally in some plants, may bind to calcium and prevent it from being absorbed optimally. These substances affect the absorption of calcium from the plant itself not the calcium contained in foods eaten at the same time. Examples of foods high in oxalic acid are spinach, collard greens, sweet potatoes, rhubarb, and beans. Foods high in phytic acid include whole grain bread, beans, seeds, nuts, grains, and soy isolates.
  • Fiber, particularly from wheat bran, could also prevent calcium absorption because of its content of phytate. However, the effect of fiber on calcium absorption is more of a concern for individuals with low calcium intakes. The average American tends to consume much less fiber per day than the level that would be needed to affect calcium absorption.

Calcium excretion refers to the amount of calcium eliminated from the body in urine, feces and sweat. Calcium excretion can be affected by many factors including:

  • Typically, dietary sodium and protein increase calcium excretion as the amount of their intake is increased. However, if a high protein, high sodium food also contains calcium, this may help counteract the loss of calcium.
  • Increasing dietary potassium intake in the presence of a high sodium diet may help decrease calcium excretion, particularly in postmenopausal women. Or decrease your intake of sodium.
  • Caffeine has a small effect on calcium absorption. It can temporarily increase calcium excretion and may modestly decrease calcium absorption, an effect easily offset by increasing calcium consumption in the diet.
  • Alcohol can affect calcium status by reducing intestinal absorption. It can also inhibit enzymes in the liver that help convert vitamin D to its active form which in turn reduces calcium absorption. The amount of alcohol required to affect calcium absorption is unknown at this time. Moderate consumption of alcohol is healthy best regardless.

As you can see, a variety of factors may cause a decrease in calcium absorption and/or increase in calcium excretion that may negatively impact your bone health. Choosing foods rich in calcium will help contribute to a lifetime of healthy bone structure.

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