Calcium processing involves absorption, utilization, and excretion. The body doesn't produce calcium; it must be obtained through diet. Absorption efficiency varies depending on several factors.
Calcium Absorption: A Multi-Step Process
Calcium absorption primarily occurs in the small intestine through two mechanisms:
- Active Transport (Transcellular): This vitamin D-dependent process utilizes specific proteins to move calcium across the intestinal cells. Calcitriol (the active form of vitamin D) and the intestinal vitamin D receptor (VDR) are crucial for this active transport.
- Passive Diffusion (Paracellular): This is a less regulated process where calcium moves between intestinal cells.
The efficiency of calcium absorption isn't constant. Several factors influence it:
- Dietary Intake: Absorption rates are higher with lower calcium intakes (around 45% at 200 mg/day) and significantly lower with higher intakes (around 15% at >2000 mg/day). [Source: NIH]
- Food Matrix: The form in which calcium is consumed impacts absorption. Different foods containing calcium have varying absorption rates. Some foods may promote calcium absorption as high as 50%. [Source: PMC]
- Age: Older adults typically absorb calcium less efficiently than younger individuals. [Source: NIH]
- Vitamin D and K: Sufficient levels of vitamin D are essential for calcium absorption. Vitamin K also plays a role in calcium utilization. Other nutrients like magnesium and phosphorus also contribute to proper calcium absorption and use. [Source: Mount Sinai]
- Gastric Acid: Stomach acid plays a vital role in calcium absorption. [Source: Physiology]
Optimal calcium absorption is aided by consuming multiple smaller doses of calcium throughout the day, ideally with meals. A suggested regimen is three 500 mg doses daily. [Source: MUSC Health]
Calcium Utilization and Excretion
Once absorbed, calcium is used for various bodily functions, including:
- Bone health: Calcium is a primary component of bones and teeth, providing structural support and strength.
- Muscle function: Calcium is involved in muscle contraction and relaxation.
- Nerve transmission: Calcium plays a role in nerve impulse transmission.
- Blood clotting: Calcium is essential for blood coagulation.
Excess calcium is excreted primarily through the kidneys in urine. The intestines also excrete a small amount of calcium in feces.
